6 - Approach to Patient

Summary

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I. HORMONE CLASSIFICATION AND RECEPTOR DYNAMICS

• The Endocrine System involves hormones secreted internally to communicate broadly with distant organs, while the Exocrine System involves secretions into external lumens or the GI tract.
• Non-glandular organs with Endocrine Function include the heart (ANP), kidneys (EPO, renin), GI tract (GLP-1, Ghrelin), and adipose tissue (Leptin).
• Glycoprotein Hormones (TSH, FSH, LH, and hCG) share a common α-subunit; specificity is determined by the distinct β-subunits.
• Clinical cross-reactivity occurs in Hyperthyroidism when very high levels of hCG stimulate the TSH receptor, leading to increased thyroid hormones and suppressed TSH.
• In the Insulin-IGF Family, tumor-produced IGF-2 can cause hypoglycemia by cross-reacting with insulin receptors.
• The PTH-PTHrP System involves two different proteins that bind the same PTH1 receptor in bone and kidney, both causing hypercalcemia and hypophosphatemia.
• Type 1 Nuclear Receptors bind steroids (Glucocorticoids, Mineralocorticoids, Androgens, Estrogens, Progesterone).
• Type 2 Nuclear Receptors bind Thyroid hormone, Vitamin D, retinoic acid, and PPAR.
• 11β-HSD (11β-hydroxysteroid dehydrogenase) is an enzyme that protects the Mineralocorticoid Receptor (MR) by converting active cortisol into inactive cortisone.
• In Cushing Syndrome, high cortisol levels saturate 11β-HSD, leading to sodium retention, potassium loss, and hypertension via MR activation.
• Estrogen Receptors (ER) have relaxed ligand specificity, allowing them to bind environmental estrogens and drugs like Tamoxifen or Raloxifene.

II. HORMONE SYNTHESIS, TRANSPORT, AND METABOLISM

• Prohormone Processing involves the cleavage of inactive precursors (e.g., Proinsulin) into active hormones (e.g., Insulin) and fragments like C-peptide.
• C-peptide is cleaved from proinsulin in secretory granules and serves as a marker of endogenous insulin production.
• POMC (Proopiomelanocortin) is a large precursor polypeptide that is processed to yield ACTH and other biologically active peptides.
• StAR (Steroidogenic Acute Regulatory) Protein is the rate-limiting factor that transports cholesterol into mitochondria for steroid synthesis.
• Thyroid Hormone Half-life: T4 has a half-life of 7 days (requires >1 month for steady state), whereas T3 has a half-life of 1 day (requires multiple daily doses).
• Serum-Binding Proteins, such as TBG (for T4/T3) and CBG (for Cortisol), provide a hormone reservoir and prevent rapid degradation.
• Only the Unbound (Free) Hormone is biologically active and available to interact with receptors.
• Liver Disease can decrease binding protein levels, while Estrogen increases levels of Thyroxine-binding globulin (TBG).
• In women with PCOS (Polycystic Ovary Syndrome), a decrease in SHBG leads to increased unbound testosterone, contributing to hirsutism.
• Pulsatile Secretion is characteristic of many peptide hormones (ACTH, GH, LH); continuous administration of GnRH actually causes pituitary desensitization.
• Hormone Degradation is essential for regulating local concentrations; Kidney failure or Liver failure can prolong hormone half-lives and cause accumulation.

III. PHYSIOLOGIC FUNCTIONS AND FEEDBACK LOOPS

• Negative Feedback is the primary regulatory mechanism where the final product (e.g., T4 or Cortisol) inhibits the release of the stimulating hormones (TRH/TSH or CRH/ACTH).
• Positive Feedback occurs during the menstrual cycle when rising Estrogen levels trigger the LH surge required for ovulation.
• Paracrine Regulation occurs when a hormone acts on an adjacent cell (e.g., Somatostatin inhibiting nearby insulin secretion).
• Autocrine Regulation occurs when a factor acts on the same cell that produced it (e.g., IGF-1 acting on chondrocytes).
• Circadian Rhythms dictate that ACTH and Cortisol peak in the early morning and reach their lowest point (nadir) at midnight.
• Stress Response is mediated by the rapid release of catecholamines and the slower, sustained release of Cortisol.

IV. PATHOLOGIC MECHANISMS AND CLINICAL EVALUATION

• MEN1 (Multiple Endocrine Neoplasia Type 1) is characterized by the triad of parathyroid, pancreatic islet, and pituitary tumors due to Menin inactivation.
• MEN2 involves medullary thyroid carcinoma, pheochromocytoma, and hyperparathyroidism due to RET protooncogene mutations.
• Immunoassays (ICMA/IRMA) are the most important diagnostic tools for measuring hormone levels due to their high sensitivity (picomolar range).
• 24-Hour Urine Collections are used to provide an integrated assessment of hormone production, bypassing the "noise" of pulsatile secretion (e.g., Urine Free Cortisol).
• Suppression Tests are used to evaluate suspected hormone hyperfunction (e.g., using Dexamethasone to suppress cortisol).
• Stimulation Tests are used to evaluate suspected hormone hypofunction (e.g., using ACTH to stimulate the adrenal gland).
• In Primary Glandular Failure, the hormone level is low but the stimulating pituitary hormone (e.g., TSH, LH) is high due to lack of negative feedback.
• In Secondary (Central) Failure, both the stimulating pituitary hormone and the target gland hormone are low.
• TSH is considered the most sensitive first-line screening test for thyroid dysfunction.
• Radiologic Imaging should only be performed after a hormonal abnormality has been biochemically confirmed.
• Common Screening Recommendations: Type 2 DM screen at age 45 (or earlier if high risk); Osteoporosis screen in women >65 years.

V. DIFFERENTIATING CLINICAL ENTITIES AND CONCEPTS

QA

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I. HORMONE CLASSIFICATION AND RECEPTOR DYNAMICS

1. What is the solubility of Amino Acid Derivatives and Peptide Hormones? | Water-soluble
2. What is the solubility of Steroid Hormones and Vitamin Derivatives? | Lipid-soluble
3. Where are the receptors for Peptide Hormones located? | Cell-surface membrane receptors
4. Where are the receptors for Steroid Hormones located? | Intracellular nuclear receptors
5. How are Peptide Hormones stored within the cell? | Secretory granules
6. How are Steroid Hormones released after synthesis? | Diffusion into circulation
7. What are examples of Water-soluble Hormones? (4) | Dopamine, Insulin, PTH, TSH
8. What are examples of Lipid-soluble Hormones? (4) | Cortisol, Estrogen, Vitamin D, Retinoids
9. What signaling mechanisms do Peptide Hormones use? | GPCRs and Kinases
10. What is the mechanism of action for Nuclear Receptors? | Alter gene transcription (DNA-binding)
11. Define the Endocrine System. | Internal secretion to distant organs
12. Define the Exocrine System. | Secretion into external lumens
13. What hormone is produced by the Heart? | Atrial Natriuretic Peptide (ANP)
14. What hormones are produced by the Kidneys? (2) | Erythropoietin and Renin
15. What hormones are produced by the GI Tract? (2) | GLP-1 and Ghrelin
16. What hormone is produced by Adipose Tissue? | Leptin
17. What common component is shared by Glycoprotein Hormones (TSH, FSH, LH, hCG)? | Alpha-subunit
18. What determines the functional specificity of Glycoprotein Hormones? | Beta-subunit
19. Why does Hyperthyroidism occur in states with very high hCG? | hCG stimulates TSH receptors
20. How can IGF-2 produced by tumors cause hypoglycemia? | Cross-reacts with insulin receptors
21. Which receptor is shared by the PTH-PTHrP System? | PTH1 receptor
22. What are the metabolic effects of PTH and PTHrP? (2) | Hypercalcemia and Hypophosphatemia
23. What types of hormones bind to Type 1 Nuclear Receptors? | Steroid hormones
24. Name the hormones that bind to Type 2 Nuclear Receptors. (4) | Thyroid hormone, Vitamin D, Retinoic acid, PPAR
25. What is the function of the enzyme 11β-HSD? | Converts cortisol to inactive cortisone
26. Which receptor is protected by 11β-HSD? | Mineralocorticoid Receptor (MR)
27. Why does Cushing Syndrome cause hypertension and potassium loss? | High cortisol saturates 11β-HSD
28. What characteristic of Estrogen Receptors allows binding of Tamoxifen? | Relaxed ligand specificity

II. HORMONE SYNTHESIS, TRANSPORT, AND METABOLISM

29. What are the precursors for Peptide Hormones? | Prohormones
30. What is the universal precursor for Steroid Hormones? | Cholesterol
31. What triggers the secretion of Peptide Hormones? (3) | Releasing factors, Ca2+, neural signals
32. What determines the secretion rate of Steroid Hormones? | Synthesis rate
33. How do Peptide Hormones usually circulate in the blood? | Freely (unbound)
34. How do Steroid Hormones travel through the blood? | Bound to serum carrier proteins
35. Compare the Half-life of Peptide vs Steroid hormones. | Peptides: Short; Steroids: Long
36. What is the half-life of Thyroxine (T4)? | 7 days
37. What process converts Proinsulin into active insulin? | Cleavage of C-peptide
38. What is the clinical significance of C-peptide? | Marker of endogenous insulin production
39. Which large precursor polypeptide is processed into ACTH? | POMC
40. What is the rate-limiting factor in Steroid Synthesis? | StAR protein
41. How long does it take for Thyroxine (T4) to reach steady state? | More than 1 month
42. What is the half-life of Triiodothyronine (T3)? | 1 day
43. Name the primary carrier protein for Thyroid Hormones. | Thyroxine-binding globulin (TBG)
44. Name the primary carrier protein for Cortisol. | Corticosteroid-binding globulin (CBG)
45. Which form of a hormone is Biologically Active? | Unbound (Free) hormone
46. How does Liver Disease affect hormone binding proteins? | Decreases levels
47. What effect does Estrogen have on TBG levels? | Increases levels
48. In PCOS, what happens to Sex Hormone-Binding Globulin (SHBG)? | Decreased levels
49. What is the clinical result of Lowered SHBG in PCOS? | Increased unbound testosterone (hirsutism)
50. What type of secretion is characteristic of Peptide Hormones (ACTH, GH, LH)? | Pulsatile secretion
51. What happens during pituitary desensitization? | Continuous GnRH administration
52. How does Renal or Hepatic failure affect hormone levels? | Prolonged half-life/accumulation

III. PHYSIOLOGIC FUNCTIONS AND FEEDBACK LOOPS

53. Which hormones regulate Growth? (3) | GH, IGF-1, Thyroid hormones
54. What determines the closure of epiphyses? | Sex steroids
55. Name hormones essential for Homeostasis. (4) | ADH, Insulin, PTH, Cortisol
56. Which hormones regulate Reproduction? (4) | GnRH, LH, FSH, Estrogen
57. Define Negative Feedback. | Final product inhibits stimulating hormones
58. When does Positive Feedback occur in the menstrual cycle? | High estrogen triggers LH surge
59. Define Paracrine Regulation. | Hormone acts on adjacent cells
60. Define Autocrine Regulation. | Factor acts on secretion cell itself
61. What is the peak time for ACTH and Cortisol? | Early morning
62. What is the nadir (lowest point) for Cortisol? | Midnight
63. Which hormones mediate the Rapid Stress Response? | Catecholamines
64. Which hormone mediates the Sustained Stress Response? | Cortisol

IV. PATHOLOGIC MECHANISMS AND CLINICAL EVALUATION

65. What are common causes of Hormone Excess? (3) | Neoplasia, Autoimmune, Iatrogenic
66. What are common causes of Hormone Deficiency? (2) | Autoimmune destruction or Infarction
67. Define Hormone Resistance. | Receptor or post-receptor defects
68. What is the triad of MEN1? | Parathyroid, Pancreatic islet, Pituitary tumors
69. What mutation causes MEN1? | Menin inactivation
70. What are the components of MEN2? (3) | Medullary thyroid, Pheochromocytoma, Hyperparathyroidism
71. What mutation causes MEN2? | RET protooncogene
72. What is the primary tool for Hormone Measurement? | Immunoassays (ICMA/IRMA)
73. Why are 24-Hour Urine Collections used? | Assess integrated production/bypass pulsatility
74. When are Suppression Tests utilized? | Suspected hormone hyperfunction
75. When are Stimulation Tests utilized? | Suspected hormone hypofunction
76. In Primary Glandular Failure, what is the level of the stimulating hormone? | High (Elevated)
77. In Secondary (Central) Failure, what is the level of the stimulating hormone? | Low or inappropriately normal
78. What is the gold standard screening for Thyroid Dysfunction? | TSH (Thyroid-Stimulating Hormone)
79. When should Radiologic Imaging be performed in endocrinology? | After biochemical confirmation
80. What is the recommended screening age for Type 2 Diabetes? | Age 45
81. What is the recommended screening age for Osteoporosis in women? | Over 65 years

V. DIFFERENTIATING CLINICAL ENTITIES AND CONCEPTS

82. Compare TSH levels in Primary vs Secondary Hypothyroidism. | Primary: High; Secondary: Low/Normal
83. Compare ACTH levels in Cushing's Disease vs Adrenal Adenoma. | Disease: High; Adenoma: Suppressed
84. Compare PTH levels in Primary HPT vs Malignancy. | Primary: High; Malignancy: Suppressed
85. Distinguish Type 1 vs Type 2 DM pathology. | Type 1: Deficiency; Type 2: Resistance
86. When does C-peptide Cleavage occur? | Posttranslational processing
87. What is the role of Dynamic Testing? | Distinguish borderline function cases
88. Why is Free Hormone measured instead of Total Hormone? | Only Free is metabolically active
89. Where do Type 1 vs Type 2 Nuclear Receptors reside initially? | Type 1: Cytoplasm; Type 2: Nucleus
90. Contrast Negative vs Positive Feedback. | Negative: Stability; Positive: Triggers events
91. Contrast the tumors of MEN 1 vs MEN 2. | MEN 1: 3Ps; MEN 2: MTC/Pheo
92. What does a high Midnight Cortisol suggest? | Cushing's Syndrome
93. What distinguishes Preproinsulin from Proinsulin? | Signal peptide for ER entry
94. How does Salsalate affect thyroid testing? | Displaces T4 from TBG
95. How does Amiodarone interfere with endocrine function? (2) | TSH receptor interference/T4 conversion blockage
96. Contrast the receptor location of Catecholamines vs Cortisol. | Catecholamines: Surface; Cortisol: Intracellular
97. What regulates the osmolality of blood? | ADH (Antidiuretic Hormone)
98. What is the precursor for Vitamin D? | Cholesterol derivative
99. Name the glycoprotein hormone used in Pregnancy Tests. | hCG
100. Define Iatrogenic hormone excess. | Caused by medical treatment/medications
101. What do Kinases do in peptide signaling? | Phosphorylate cellular proteins
102. What is Menin? | Tumor suppressor protein (MEN1)
103. Define Pheochromocytoma. | Catecholamine-secreting adrenal tumor (MEN2)
104. What does Urine Free Cortisol measure? | 24-hour integrated cortisol production
105. What is the stimulus for Dexamethasone Suppression Test? | Synthetic glucocorticoid
106. What is the stimulus for ACTH Stimulation Test? | Cosyntropin
107. Which gland fails in Addison's Disease? | Adrenal gland
108. Which gland fails in Hashimoto's? | Thyroid gland
109. What happens to FSH in Primary Ovarian Failure? | Becomes elevated
110. What metabolic condition is caused by PTH1 receptor activation? | Hypercalcemia
111. What is the role of PPAR receptors? | Metabolic regulation/Gene transcription
112. How does Raloxifene act on estrogen receptors? | Selective modulation
113. Define the Circadian Rhythm nadir. | The lowest concentration point
114. What constitutes the adrenal axis components? | CRH, ACTH, Cortisol
115. What constitutes the thyroid axis components? | TRH, TSH, T4/T3
116. Contrast prohormone Storage vs synthesis. | Stored in granules before secretion
117. What does the StAR protein transport? | Cholesterol into mitochondria
118. What defines Hirsutism in PCOS? | Excessive terminal hair growth
119. What is the clinical name for Low T4 and High TSH? | Primary Hypothyroidism
120. What is the clinical name for Low T4 and Low TSH? | Secondary Hypothyroidism

7

Summary

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I. EPIDEMIOLOGY AND CLASSIFICATION OF DIABETES MELLITUS

• Global Burden: Diabetes is a leading worldwide health problem; 55% of individuals with diabetes reside in the Southeast Asia and Western Pacific Regions.
• HbA1C Target: For Filipino patients, the target glycemic average is an HbA1C of 7% (estimated average glucose of 154 mg/dL).
• Type 1 Diabetes Mellitus (T1DM): Characterized by complete or near total insulin deficiency due to an autoimmune attack on pancreatic beta cells; frequently associated with HLA-DR3/DR4 genes.
• Type 2 Diabetes Mellitus (T2DM): Characterized by a triad of insulin resistance, impaired insulin secretion, and increased hepatic glucose production.
• Gestational Diabetes Mellitus (GDM): Defined as glucose intolerance first developing during the second or third trimester of pregnancy.
• Overt Diabetes in Pregnancy: Diabetes diagnosed during the initial prenatal visit (first trimester) is classified as preexisting pregestational diabetes, not GDM.
• GDM Future risk: Women with GDM have a 35-60% risk of developing DM within 10-20 years and require screening at least every 3 years lifelong.
• Maturity-Onset Diabetes of the Young (MODY): A form of monogenic diabetes characterized by autosomal dominant inheritance, early onset (usually <25 years), and impaired insulin secretion.
• Ketosis-Prone T2DM: Seen in African American or Asian heritage; patients present with ketoacidosis (typical of T1) but do not require long-term insulin and can eventually be managed with oral agents.
• Latent Autoimmune Diabetes in Adults (LADA): Also called autoimmune diabetes of adults; presents phenotypically like T2DM but possesses islet antibodies and progresses to insulin dependence.
• Fulminant Diabetes: A form of acute-onset Type 1 DM (noted in Japan) potentially triggered by viral infections.

II. DIAGNOSTIC CRITERIA AND SCREENING

• Fasting Plasma Glucose (FPG): Normal is <100 mg/dL; Diabetes is ≥126 mg/dL.
• HbA1C Levels: Normal is <5.7%; Prediabetes is 5.7%-6.4%; Diabetes is ≥6.5%.
• Oral Glucose Tolerance Test (OGTT): Normal 2-h PG is <140 mg/dL; Impaired Glucose Tolerance (IGT) is 140-199 mg/dL; Diabetes is ≥200 mg/dL.
• Random Plasma Glucose: ≥200 mg/dL in a patient with classic symptoms (polyuria, polydipsia, weight loss) is diagnostic of Diabetes.
• Confirmatory Testing: Unless there is clear clinical diagnosis (e.g., hyperglycemic crisis), abnormal screening tests must be repeated to confirm diagnosis.
• General Screening Recommendation: Screen all individuals starting at age 45 every 3 years; screen earlier if BMI >25 kg/m² (or ethnic equivalent) plus one additional risk factor.
• Triple Catabolic Symptoms: The presumptive symptoms of DM are Polydipsia (thirst), Polyuria (excessive urine), and unintentional weight loss.

III. PATHOGENESIS OF TYPE 1 AND TYPE 2 DM

• T1DM Genetic Risk: The HLA region on Chromosome 6 (MHC Class II) is the major susceptibility locus, specifically DR3 and/or DR4 haplotypes.
• T1DM Clinical Presentation: Often has an acute, dramatic onset; 25-50% present with Diabetic Ketoacidosis (DKA) at initial diagnosis.
• T1DM Autoantibodies: Presence of GAD-65, ICA-512 (IA-2), and Zinc transporter (ZnT-8) antibodies helps document the autoimmune process.
• Honey-moon Phase: In T1DM, a transient period of low insulin requirement or insulin independence may occur shortly after diagnosis before absolute deficiency occurs.
• T1DM Environmental Triggers: Proposed triggers for autoimmunity include Coxsackie virus, rubella, bovine milk proteins, and Vitamin D deficiency.
• T2DM Postreceptor Defects: The precise molecular mechanism of insulin resistance involves "postreceptor" defects in insulin-regulated phosphorylation/dephosphorylation.
• T2DM Hepatic Glucose: Insulin resistance in the liver results in a failure to suppress gluconeogenesis, leading to fasting hyperglycemia.
• T2DM Adipose Tissue: Resistance leads to increased lipolysis and free fatty acid (FFA) flux, which predisposes to NAFLD/steatosis and abnormal liver function tests.
• Ominous Octet / Egregious Eleven: Pathogenic models for T2DM that include defects in the pancreas (alpha/beta cells), gut (incretin effect), kidneys (glucose reabsorption), brain, liver, muscle, and adipose tissue.
• Asian Phenotype (T2DM): Asians often have a lower BMI, higher propensity for visceral obesity, and reduced pancreatic beta-cell mass compared to Western populations.

IV. PHARMACOLOGIC MANAGEMENT: INSULIN THERAPY

• Basal Insulin: Essential for regulating glycogen breakdown and gluconeogenesis; include NPH, Glargine, Detemir, and Degludec.
• Prandial (Mealtime) Insulin: Required for postprandial glucose utilization; rapid-acting analogs (Lispro, Aspart, Glulisine) or Regular insulin.
• Rapid-acting Insulin Analogs: Onset in less than 15 minutes ; peak in 0.5-1.5 hours; duration 3-4 hours; should be given &lt10 mins before or after a meal.
• Short-acting (Regular) Insulin: Onset in 0.5-1.0 hour; peak in 2-3 hours; should be given 30-45 mins before a meal.
• Intermediate-acting (NPH) Insulin: Onset in 1-4 hours; peak in 6-10 hours; duration 10-16 hours.
• Long-acting Insulin (Glargine/Degludec): Provide peakless coverage; Degludec has a duration of action of 30 hours.
• Total Daily Dose (TDD): Estimated at 0.5-1.0 U/kg/day; typically split 50% basal and 50% bolus (prandial).
• Dawn Phenomenon: Early morning hyperglycemia due to nocturnal growth hormone and cortisol secretion; requires adjustment of basal insulin.
• Premixed Insulins: Usually administered twice daily; the smaller number in the ratio represents the short-acting component (e.g., 70/30).
• Continuous Subcutaneous Insulin Infusion (CSII): Insulin pumps use rapid-acting insulin only to provide both basal and bolus doses; highly effective for T1DM.

V. PHARMACOLOGIC MANAGEMENT: NON-INSULIN AGENTS

• Metformin (Biguanide): The preferred initial agent for T2DM; reduces hepatic glucose production; weight neutral; most common side effect is GI upset.
• Metformin Contraindication: Should be stopped if eGFR &lt30 mL/min/1.73m² due to the risk of lactic acidosis.
• Sulfonylureas (SU): Insulin secretagogues (e.g., Glimepiride); high HbA1C lowering efficacy but carry high risk of hypoglycemia and weight gain.
• TZDs (Thiazolidinediones): Insulin sensitizers (e.g., Pioglitazone); no hypoglycemia risk; side effects include weight gain, fluid retention/HF risk, and bone fractures.
• DPP-4 Inhibitors (Gliptins): Enhance incretin action; weight neutral with no hypoglycemia; Linagliptin and Teneligliptin do not require dose adjustment for renal failure.
• SGLT2 Inhibitors (-flozins): Promote urinary glucose excretion; offer significant CV and renal benefits; risk of euglycemic DKA and genital mycotic infections.
• GLP-1 Receptor Agonists: Injectables (e.g., Liraglutide, Semaglutide); provide high efficacy for weight loss and CV benefit; most common side effect is nausea.

VI. ACUTE COMPLICATIONS: DKA AND HHS

• Diabetic Ketoacidosis (DKA) Triad: Hyperglycemia (>250 mg/dL), Metabolic Acidosis (pH <7.3, HCO₃ <18), and Increased Ketones; primary ketone is beta-hydroxybutyrate.
• DKA Pathophysiology: Absolute or relative insulin deficiency plus excess counterregulatory hormones leading to massive lipolysis and ketogenesis.
• Hyperosmolar Hyperglycemic State (HHS) Hallmark: Severe Hyperglycemia (>1000 mg/dL), Hyperosmolality (>300 mOsm/L), and profound dehydration without significant acidosis/ketones.
• HHS Epidemiology: Most commonly presents in elderly T2DM patients with diminished oral intake or acute stressors (MI, sepsis).
• Euglycemic DKA: Ketosis occurring with glucose levels 200-250 mg/dL; most commonly associated with SGLT2 inhibitor use.
• DKA/HHS Fluid Management: Initial therapy is 0.9% Normal Saline (1-3 L over 2-3 h); switch to 0.45% saline if Na+ >150 mEq/L.
• Insulin in Crisis: IV bolus of 0.1 unit/kg followed by an infusion of 0.1 unit/kg/hr; add dextrose to fluids once glucose reaches 200-250 mg/dL.

VII. CHRONIC MICROVASCULAR COMPLICATIONS

• Diabetic Retinopathy: Leading cause of new blindness in adults 20-74; features include microaneurysms, hemorrhages, cotton-wool spots, and neovascularization.
• Retinopathy Screening: Screen T2DM at diagnosis; T1DM 5 years after onset; then annually.
• Diabetic Nephropathy: Leading cause of End-Stage Renal Disease (ESRD); hallmark pathologic lesion is the Kimmelstiel-Wilson (KW) nodule.
• Nephropathy Screening: Measured by Estimated GFR (eGFR) and Urinary Albumin-to-Creatinine Ratio (UACR); abnormal UACR is ≥30 mg/g (confirmed by 2 of 3 specimens).
• Nephropathy Management: First-line for HTN in DM with albuminuria are ACE Inhibitors or ARBs (never used in combination or during pregnancy).
• Symmetric Peripheral Polyneuropathy: The most common form of neuropathy; presents as sensory loss in a "stocking-glove" distribution, often symptomatic at night.
• Loss of Protective Sensation (LOPS): Screened using a 10-g monofilament; lack of feeling in 4 or more points indicates neuropathy and high risk for ulcers/amputation.
• Cardiac Autonomic Neuropathy (CAN): Independent risk factor for CV mortality; presents as resting tachycardia or orthostatic hypotension.
• Gastrointestinal Autonomic Neuropathy: Includes gastroparesis (anorexia, nausea, early satiety) and diabetic enteropathy (diarrhea/constipation).

VIII. CHRONIC MACROVASCULAR AND SYSTEMIC MANAGEMENT

• Aspirin Therapy: Used for secondary prevention in DM with history of CVD; use Clopidogrel if aspirin allergy is present.
• Statin Therapy: Recommended for all DM patients over age 40 or those with overt CVD regardless of cholesterol levels.
• Foot Care Essentials: Clean feet daily with warm water; never soak; moisturize (not between toes); cut nails to the shape of the toe; always wear shoes/slippers.
• Blood Pressure Targets: Generally &lt140/80 mmHg; <130/80 mmHg for younger patients with higher risk.
• Lipid Targets: LDL &lt100 mg/dL (<70 mg/dL for those with overt CVD); Triglycerides &lt150 mg/dL.

IX. COMPARATIVE SUMMARY OF CLINICAL ENTITIES

QA

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I. EPIDEMIOLOGY AND CLASSIFICATION OF DIABETES MELLITUS

1. Where do 55% of individuals with Diabetes reside? | Southeast Asia and Western Pacific
2. What is the target HbA1C for Filipino patients? | 7%
3. What is the estimated average glucose corresponding to an HbA1C of 7%? | 154 mg/dL
4. What is the primary characteristic of Type 1 Diabetes Mellitus? | Complete or near total insulin deficiency
5. What is the cause of beta cell destruction in Type 1 DM? | Autoimmune attack
6. Which genes are frequently associated with Type 1 DM? | HLA-DR3/DR4
7. What are the triad characteristics of Type 2 Diabetes Mellitus? (3) | 1) Insulin resistance
   2) Impaired insulin secretion
   3) Increased hepatic glucose production
8. What is the definition of Gestational Diabetes Mellitus? | Glucose intolerance first developing during 2nd or 3rd trimester
9. How is diabetes diagnosed at the initial prenatal visit classified? | Preexisting pregestational diabetes
10. What is the 10-20 year future risk of DM for women with GDM? | 35-60%
11. How often should women with a history of GDM be screened? | Every 3 years lifelong
12. What are the features of Maturity-Onset Diabetes of the Young (MODY)? (3) | 1) Autosomal dominant inheritance
    2) Early onset (<25 years)
    3) Impaired insulin secretion
13. Which heritage is most associated with Ketosis-Prone T2DM? | African American or Asian
14. Do patients with Ketosis-Prone T2DM require long-term insulin? | No
15. What is the phenotypic presentation of Latent Autoimmune Diabetes in Adults (LADA)? | Phenotypically like T2DM
16. What does LADA possess that leads to insulin dependence? | Islet antibodies
17. What is Fulminant Diabetes? | Acute-onset Type 1 DM
18. What is a potential trigger for Fulminant Diabetes? | Viral infections

II. DIAGNOSTIC CRITERIA AND SCREENING

19. What is a normal Fasting Plasma Glucose (FPG) level? | < 100 mg/dL
20. What Fasting Plasma Glucose (FPG) level is diagnostic of Diabetes? | ≥ 126 mg/dL
21. What is a normal HbA1C level? | < 5.7%
22. What HbA1C range is diagnostic of Prediabetes? | 5.7%-6.4%
23. What HbA1C level is diagnostic of Diabetes? | ≥ 6.5%
24. What is a normal 2-h PG during an OGTT? | < 140 mg/dL
25. What 2-h OGTT range defines Impaired Glucose Tolerance (IGT)? | 140-199 mg/dL
26. What 2-h OGTT level is diagnostic of Diabetes? | ≥ 200 mg/dL
27. What Random Plasma Glucose level is diagnostic with classic symptoms? | ≥ 200 mg/dL
28. What are the Triple Catabolic Symptoms of DM? (3) | 1) Polydipsia
    2) Polyuria
    3) Unintentional weight loss
29. How must abnormal screening tests be handled if there is no hyperglycemic crisis? | They must be repeated
30. What is the general screening recommendation for age and frequency? | Age 45 every 3 years
31. When should screening occur earlier than age 45? (2) | 1) BMI > 25 kg/m²
    2) One additional risk factor

III. PATHOGENESIS OF TYPE 1 AND TYPE 2 DM

32. What is the major susceptibility locus for T1DM genetic risk? | HLA region on Chromosome 6
33. Which specific HLA haplotypes are linked to T1DM? | DR3 and/or DR4
34. What percentage of T1DM patients present with DKA at diagnosis? | 25-50%
35. Name the autoantibodies used to document T1DM. (3) | GAD-65, ICA-512 (IA-2), and ZnT-8
36. What is the Honey-moon Phase in T1DM? | Transient period of insulin independence
37. Name the proposed environmental triggers for T1DM. (4) | Coxsackie virus, rubella, bovine milk, Vitamin D deficiency
38. What molecular mechanism is involved in T2DM insulin resistance? | Postreceptor defects
39. Insulin resistance in the liver leads to what failure? | Failure to suppress gluconeogenesis
40. What is the result of increased lipolysis in T2DM adipose tissue? | NAFLD/steatosis
41. What pathogenic models describe the multiple defects in T2DM? | Ominous Octet / Egregious Eleven
42. Name organs involved in the Ominous Octet. (5) | Pancreas, gut, kidneys, liver, muscle
43. Describe the Asian Phenotype of T2DM compared to Westerners. (3) | 1) Lower BMI
    2) Visceral obesity
    3) Reduced beta-cell mass

IV. PHARMACOLOGIC MANAGEMENT: INSULIN THERAPY

44. What processes does Basal Insulin regulate? | Glycogen breakdown and gluconeogenesis
45. Name examples of Basal Insulin. (4) | NPH, Glargine, Detemir, Degludec
46. What is the purpose of Prandial Insulin? | Postprandial glucose utilization
47. Name Rapid-acting Insulin analogs. (3) | Lispro, Aspart, Glulisine
48. What is the onset of Rapid-acting Insulin analogs? | < 15 minutes
49. What is the peak of Rapid-acting Insulin analogs? | 0.5-1.5 hours
50. When should Rapid-acting Insulin be administered? | < 10 mins before/after meal
51. What is the onset of Short-acting (Regular) Insulin? | 0.5-1.0 hour
52. When should Regular Insulin be given? | 30-45 mins before meal
53. What is the peak of Intermediate-acting (NPH) Insulin? | 6-10 hours
54. What is the duration of NPH? | 10-16 hours
55. What is the hallmark feature of Long-acting Insulin? | Peakless coverage
56. What is the duration of action of Degludec? | 30 hours
57. What is the estimated Total Daily Dose (TDD) of insulin? | 0.5-1.0 U/kg/day
58. What is the typical split for TDD? | 50% basal and 50% bolus
59. What causes the Dawn Phenomenon? | Nocturnal growth hormone and cortisol
60. How many times daily are Premixed Insulins usually given? | Twice daily
61. What does the smaller number in a premixed ratio represent? | Short-acting component
62. What type of insulin is used in CSII (Insulin pumps)? | Rapid-acting insulin only

V. PHARMACOLOGIC MANAGEMENT: NON-INSULIN AGENTS

63. What is the preferred initial agent for T2DM? | Metformin
64. What is the mechanism of Metformin? | Reduces hepatic glucose production
65. What is the most common side effect of Metformin? | GI upset
66. At what eGFR level must Metformin be stopped? | < 30 mL/min/1.73m²
67. What is the severe risk of Metformin in renal failure? | Lactic acidosis
68. What is the mechanism of Sulfonylureas (SU)? | Insulin secretagogues
69. What are the primary risks of Sulfonylureas? (2) | 1) Hypoglycemia
    2) Weight gain
70. What is the mechanism of TZDs (Pioglitazone)? | Insulin sensitizers
71. Name the side effects of TZDs. (3) | Weight gain, fluid retention, fractures
72. Which DPP-4 Inhibitors do not require renal dose adjustment? | Linagliptin and Teneligliptin
73. What is the mechanism of SGLT2 Inhibitors? | Promote urinary glucose excretion
74. Name the benefits of SGLT2 Inhibitors (-flozins). | CV and renal benefits
75. What are the risks of SGLT2 Inhibitors? (2) | Euglycemic DKA and genital infections
76. What are the benefits of GLP-1 Receptor Agonists? | Weight loss and CV benefit
77. What is the common side effect of GLP-1 Agonists? | Nausea

VI. ACUTE COMPLICATIONS: DKA AND HHS

78. What is the DKA Triad? (3) | 1) Hyperglycemia (>250)
    2) Acidosis (pH <7.3)
    3) Ketones
79. What is the primary ketone in DKA? | Beta-hydroxybutyrate
80. What causes massive lipolysis in DKA? | Insulin deficiency + counterregulatory hormones
81. What is the hallmark of HHS? | Hyperglycemia >1000 and Hyperosmolality
82. Does HHS present with significant acidosis? | No
83. Which patient population most commonly presents with HHS? | Elderly T2DM patients
84. What glucose level is seen in Euglycemic DKA? | < 200-250 mg/dL
85. Which drug class is associated with Euglycemic DKA? | SGLT2 inhibitors
86. What is the initial fluid therapy for DKA/HHS? | 0.9% Normal Saline (1-3 L)
87. When is fluid switched to 0.45% saline in DKA? | If Na+ > 150 mEq/L
88. What is the initial insulin dose in DKA crisis? | 0.1 unit/kg bolus
89. When should dextrose be added to DKA fluids? | Glucose < 200-250 mg/dL

VII. CHRONIC MICROVASCULAR COMPLICATIONS

90. What is the leading cause of new blindness in adults? | Diabetic Retinopathy
91. Name clinical features of Diabetic Retinopathy. (3) | Microaneurysms, hemorrhages, cotton-wool spots
92. When is the first retinopathy screening for T2DM? | At diagnosis
93. When is the first retinopathy screening for T1DM? | 5 years after onset
94. What is the leading cause of ESRD? | Diabetic Nephropathy
95. What is the hallmark pathologic lesion of Diabetic Nephropathy? | Kimmelstiel-Wilson (KW) nodule
96. How is Nephropathy screened? (2) | eGFR and UACR
97. What UACR level is considered abnormal? | ≥ 30 mg/g
98. What are the first-line agents for HTN with DM albuminuria? | ACE Inhibitors or ARBs
99. True or False: ACE Inhibitors and ARBs can be used together. | False
100. What is the most common form of diabetic neuropathy? | Symmetric Peripheral Polyneuropathy
101. Describe the sensory loss distribution in diabetic neuropathy. | Stocking-glove distribution
102. When are neuropathy symptoms often worse? | At night
103. What tool is used to screen for Loss of Protective Sensation (LOPS)? | 10-g monofilament
104. How many points not felt on monofilament test indicate high risk? | 4 or more points
105. What are signs of Cardiac Autonomic Neuropathy (CAN)? (2) | Resting tachycardia, orthostatic hypotension
106. Name symptoms of Gastroparesis. (3) | Anorexia, nausea, early satiety

VIII. CHRONIC MACROVASCULAR AND SYSTEMIC MANAGEMENT

107. When is Aspirin used in DM management? | Secondary prevention of CVD
108. What is the alternative if a patient has an aspirin allergy? | Clopidogrel
109. Who should receive Statin Therapy? | All DM over age 40
110. List Foot Care Essentials. (4) | 1) Clean daily
     2) Never soak
     3) Moisturize
     4) Always wear shoes
111. What is the general Blood Pressure Target for DM? | < 140/80 mmHg
112. What is the LDL Target for DM without overt CVD? | < 100 mg/dL
113. What is the LDL Target for DM with overt CVD? | < 70 mg/dL
114. What is the Triglyceride Target for DM? | < 150 mg/dL

IX. COMPARATIVE SUMMARY (TABLES)

115. Compare the Primary Defect: T1DM vs T2DM. | T1: Beta-cell destruction
     T2: Resistance + exhaustion
116. Compare Body Habitus: T1DM vs T2DM. | T1: Lean
     T2: Obese/Overweight
117. Compare Insulin Levels: T1DM vs T2DM. | T1: Low/Undetectable
     T2: High early, Low late
118. Which DM type is strongly associated with HLA (DR3/DR4)? | Type 1 DM
119. Compare Glucose Levels: DKA vs HHS. | DKA: > 250 mg/dL
     HHS: > 600-1000+ mg/dL
120. Compare Dehydration Degree: DKA vs HHS. | DKA: Moderate
     HHS: Severe/Profound
121. Compare Ketone Presence: DKA vs HHS. | DKA: Markedly Positive
     HHS: Absent or trace
122. Compare Serum Bicarbonate: DKA vs HHS. | DKA: Low (<18)
     HHS: Relatively Normal (>18)
123. What is the Goal of Rapid-acting/Short-acting insulin? | Mealtime coverage/bolus
124. What is the Peak of Short-acting (Regular) insulin? | 2-3 hours
125. What is the Peak of Long-acting insulin? | Peakless
126. Significance: 128-Hz Tuning Fork. | Vibration Sensation
127. Significance: Ankle Reflexes. | Nerve Function/Achilles reflex
128. Abnormal Finding: 10-g Monofilament. | < 4/10 sites felt
129. Abnormal Finding: Visual Inspection of feet. | Deformities, calluses, ulcers
130. What is the leading world health problem regarding blood sugar? | Diabetes
131. In what trimester does GDM typically develop? | Second or third
132. What is LADA also known as? | Autoimmune diabetes of adults
133. What is the normal PG level 2 hours post-OGTT? | < 140 mg/dL
134. What is the major locus on Chromosome 6 for T1DM? | HLA region
135. What does T2DM resistance in adipose tissue lead to? | Increased lipolysis/FFA flux
136. Name rapid-acting insulin types. (3) | Aspart, Lispro, Glulisine
137. Name long-acting insulin types. (3) | Glargine, Detemir, Degludec
138. What describes early morning hyperglycemia? | Dawn Phenomenon
139. What is the preferred agent for initial T2DM? | Metformin
140. Which drug class causes fluid retention? | TZDs (Thiazolidinediones)
141. What is the risk of SGLT2 inhibitors regarding infections? | Genital mycotic infections
142. What pH defines Metabolic Acidosis in DKA? | pH < 7.3
143. What osmolality is seen in HHS? | > 300 mOsm/L
144. What defines blindness risk in diabetics? | Diabetic Retinopathy
145. What lesion is pathognomonic for Nephropathy? | Kimmelstiel-Wilson nodule
146. What distribution defines Symmetric Polyneuropathy? | Stocking-glove
147. What is CAN an independent risk factor for? | CV mortality
148. What should be used for Secondary Prevention in CVD? | Aspirin
149. What is the target Triglyceride level? | < 150 mg/dL
150. What age starts DM screening? | Age 45

8

Summary

text

I. PITUITARY ANATOMY, DEVELOPMENT, AND PHYSIOLOGY

• The Anterior Pituitary produces six major hormones: Prolactin (PRL), Growth Hormone (GH), Adrenocorticotropic Hormone (ACTH), Luteinizing Hormone (LH), Follicle-Stimulating Hormone (FSH), and Thyroid-Stimulating Hormone (TSH).
• The Pituitary Gland is known as the "master gland" because it orchestrates the regulatory functions of many other endocrine glands.
• The Anterior Pituitary blood supply is derived from the hypothalamic-pituitary portal plexus, allowing releasing/inhibiting hormones to reach it without systemic dilution.
• Anterior Pituitary Hormones are secreted in a pulsatile manner.
• The Pituitary Gland weighs approximately 600 mg and sits within the sella turcica.
• Prop-1 is a transcription factor that induces the development of Pit-1-specific lineages and gonadotropes; it is the most common cause of familial Combined Pituitary Hormone Deficiency (CPHD).
• Pit-1 (POU1F1) is a transcription factor required for the development of somatotropes (GH), lactotropes (PRL), and thyrotropes (TSH).
• T-Pit is a transcription factor required for the development of corticotrope cells which express the POMC gene.
• SF-1 and DAX-1 are nuclear receptors that define gonadotrope cell development.

II. DEVELOPMENTAL AND HYPOTHALAMIC CAUSES OF HYPOPITUITARISM

• Kallmann Syndrome results from defective hypothalamic GnRH synthesis and is often linked to X-linked KAL gene mutations.
• Kallmann Syndrome treatment in males involves human chorionic gonadotropin (hCG) or testosterone; in females, cyclic estrogen and progestin are used.
• Leptin or Leptin Receptor Mutations cause hyperphagia, obesity, and central hypogonadism.

III. ACQUIRED HYPOPITUITARISM

• Cranial Irradiation causes hormone loss in a typical pattern: GH deficiency is the most common, followed by gonadotropins, TSH, and ACTH.
• Lymphocytic Hypophysitis occurs most often in postpartum women, presenting with hyperprolactinemia and a pituitary mass that resembles an adenoma.
• Lymphocytic Hypophysitis is characterized by an elevated erythrocyte sedimentation rate (ESR) and often resolves with glucocorticoid treatment.
• Pituitary Apoplexy is an endocrine emergency caused by acute hemorrhagic vascular events, often in a pre-existing adenoma or postpartum (Sheehan's).
• Pituitary Apoplexy clinical features include severe headache, meningeal irritation, visual changes, and potential cardiovascular collapse.
• Empty Sella is often an incidental finding where the sella is filled with CSF; pituitary function is usually normal.
• CTLA-4 Inhibitors (e.g., Ipilimumab) can cause hypophysitis with associated thyroid, adrenal, and gonadal failure in up to 20% of patients.
• The Order of Hormone Loss in acquired pituitary failure is typically: GH → FSH/LH → TSH → ACTH.

IV. CLINICAL FEATURES AND EVALUATION OF HORMONE DEFICIENCIES

• GH Deficiency causes growth disorders in children and increased fat mass/decreased lean muscle in adults.
• Secondary Hypothyroidism is diagnosed by finding low free T4 with a low or inappropriately normal TSH.
• Secondary Adrenal Insufficiency (ACTH deficiency) features hypocortisolism but preserves mineralocorticoid production; unlike primary failure, there is no hyperpigmentation.
• Insulin Tolerance Test (ITT) is the gold standard for assessing GH and ACTH reserve; a normal response is a GH increase >5 µg/L when glucose is <40 mg/dL.
• Adult GH Deficiency (AGHD) is defined by a peak GH response to hypoglycemia of &lt3 µg/L.
• ITT is contraindicated in patients with epilepsy, ischemic heart disease, or the elderly.
• Gonadotropin Deficiency is the most common presenting feature of adult hypopituitarism (loss of libido, infertility, amenorrhea).

V. PITUITARY ADENOMAS AND MASS EFFECTS

• Pituitary Adenomas are benign neoplasms categorized as microadenomas (<1 cm) or macroadenomas (>1 cm).
• Optic Chiasm Compression by a suprasellar mass typically leads to bitemporal hemianopia (often superiorly pronounced).
• Stalk Section Phenomenon occurs when a mass compresses the pituitary stalk, blocking dopamine and causing hyperprolactinemia.
• Cavernous Sinus Invasion can lead to palsies of CN III, IV, and VI, causing diplopia and ptosis.
• Prolactinoma is the most common pituitary hormone hypersecretion syndrome.
• Transsphenoidal Surgery is the desired approach for most pituitary tumors, except rare invasive suprasellar masses.
• Stereotactic Radiosurgery (Gamma Knife) is used as an adjunct to surgery, especially for residual nonfunctioning tumors.

VI. SPECIFIC HYPERSECRETORY SYNDROMES

• Prolactinoma treatment: Cabergoline is preferred due to higher efficacy; Bromocriptine is preferred if pregnancy is desired.
• Acromegaly diagnosis is confirmed by the failure of GH to suppress to &lt0.4 µg/L after a 75g oral glucose load.
• Acromegaly physical signs include frontal bossing, enlarged hands/feet, macroglossia, and carpal tunnel syndrome.
• Pegvisomant (GH receptor antagonist) normalizes IGF-1 by blocking peripheral GH binding but does not shrink the tumor.
• Cushing’s Disease (pituitary ACTH) must be distinguished from ectopic ACTH; Inferior Petrosal Sinus Sampling (IPSS) with a CRH peak ratio ≥3 confirms a pituitary source.
• Nelson’s Syndrome is the rapid enlargement of a pituitary tumor and hyperpigmentation following bilateral adrenalectomy for Cushing’s.
• Nonfunctioning Adenomas are usually macroadenomas that present with visual loss and slightly elevated PRL (due to stalk effect).

VII. EXPERT COMPARISONS AND DIFFERENTIATION

1. Primary vs. Secondary Hypothyroidism: Primary has High TSH; Secondary (pituitary) has Low/Normal TSH despite low T4.
2. Primary vs. Secondary Adrenal Insufficiency: Primary (Addison's) features hyperpigmentation and mineralocorticoid loss; Secondary (ACTH def) lacks hyperpigmentation and preserves aldosterone.
3. Pit-1 vs. PROP-1 Mutation: Pit-1 affects GH, PRL, TSH; PROP-1 affects those PLUS Gonadotropins (LH/FSH).
4. Microadenoma vs. Macroadenoma: Microadenomas are &lt1 cm; Macroadenomas are >1 cm and cause mass effects.
5. Cabergoline vs. Bromocriptine: Cabergoline is long-acting (twice weekly) and more effective; Bromocriptine is short-acting and safer for fertility.
6. Pituitary Cushing’s vs. Ectopic ACTH: Pituitary Cushing's usually shows partial suppression with high-dose dexamethasone; Ectopic ACTH is unresponsive and has higher K+ depletion.
7. SRLs (Octreotide) vs. Pegvisomant: SRLs inhibit GH secretion and shrink tumors; Pegvisomant blocks the receptor and lowers IGF-1 without shrinking the tumor.
8. Kallmann Syndrome vs. Bardet-Biedl: Both have GnRH deficiency, but Kallmann features anosmia while Bardet-Biedl features polydactyly/obesity.
9. Bitemporal vs. Homonymous Hemianopia: Bitemporal denotes chiasm compression (pituitary); Homonymous denotes post-chiasmal compression.
10. TSH-secreting Adenoma vs. Resistance to Thyroid Hormone: Adenomas usually have a visible pituitary mass and elevated alpha-subunit; Resistance does not.
11. Insulin Tolerance Test vs. Glucose Suppression Test: ITT tests for Hormone Deficiency (GH/ACTH); Glucose load tests for Hormone Excess (Acromegaly).
12. Lymphocytic Hypophysitis vs. Pituitary Adenoma: Hypophysitis is usually postpartum with a high ESR; Adenomas are more common and not inflammatory.
13. Iatrogenic Cushing’s vs. Cushing’s Disease: Iatrogenic is the most common cause of cushingoid features due to exogenous steroids; Disease is due to pituitary ACTH hypersecretion.
14. Diabetes Insipidus (Central): Caused by loss of Vasopressin (ADH) from the posterior pituitary, resulting in polyuria/polydipsia.
15. Acromegaly vs. Gigantism: Acromegaly occurs after epiphyses close (adults); Gigantism occurs before epiphyses close (children).
16. Pasireotide vs. Octreotide: Pasireotide has higher affinity for SST5 (better for Cushing's) and a higher risk of hyperglycemia/diabetes.
17. Stalk Effect Hyperprolactinemia vs. Prolactinoma: Stalk effect PRL levels are usually &lt100-200 µg/L; Prolactinomas often result in PRL >250 µg/L.
18. Metyrapone vs. Ketoconazole: Both inhibit cortisol synthesis; Ketoconazole is an antifungal, while Metyrapone is a specific 11β-hydroxylase inhibitor.
19. MEN1 vs. Non-Syndromic Pituitary Tumor: MEN1 involves the 3 Ps (Pituitary, Parathyroid, Pancreas) due to menin mutation.
20. Prader-Willi vs. Obesity-related Hypogonadism: Prader-Willi is a genetic syndrome with hypotonia and "paternal deletion"; simple obesity isn't.

QA

text

I. PITUITARY ANATOMY, DEVELOPMENT, AND PHYSIOLOGY

1. Which structure produces the hormones PRL, GH, ACTH, LH, FSH, and TSH? | Anterior Pituitary
2. List the six major hormones produced by the Anterior Pituitary. | PRL, GH, ACTH,
   LH, FSH, TSH
3. Why is the Pituitary Gland referred to as the "master gland"? | Orchestrates other endocrine glands
4. From where is the blood supply of the Anterior Pituitary derived? | Hypothalamic-pituitary portal plexus
5. What is the functional advantage of the hypothalamic-pituitary portal plexus? | Prevents systemic hormone dilution
6. Characterize the secretion pattern of Anterior Pituitary Hormones. | Pulsatile manner
7. What is the approximate weight of the Pituitary Gland? | 600 mg
8. Name the bony structure where the Pituitary Gland is located. | Sella turcica
9. Which transcription factor induces Pit-1-specific lineages and gonadotropes? | Prop-1
10. What is the most common cause of familial Combined Pituitary Hormone Deficiency (CPHD)? | Prop-1 mutation
11. Name the transcription factor required for GH, PRL, and TSH development. | Pit-1 (POU1F1)
12. Development of which cells depends on the transcription factor Pit-1? (3) | Somatotropes, lactotropes, and thyrotropes
13. Which transcription factor is required for corticotrope cell development? | T-Pit
14. Which gene is expressed by corticotrope cells under the influence of T-Pit? | POMC gene
15. Which nuclear receptors define the development of gonadotrope cells? (2) | SF-1 and DAX-1

II. DEVELOPMENTAL AND HYPOTHALAMIC CAUSES OF HYPOPITUITARISM

16. Which hormones are deficient in a Pit-1 Mutation? (3) | GH, PRL, and TSH
17. Identify the clinical features of Pit-1 Mutation. (2) | Growth failure and
    hypoplastic pituitary gland
18. Which hormones are deficient in PROP1 Mutation? (4) | GH, PRL, TSH,
    and Gonadotropins
19. What is a key developmental feature of PROP1 Mutation by adulthood? | Universal TSH/Gn deficiency
20. Which hormone is isolated in its deficiency during a TPIT Mutation? | ACTH
21. List clinical features of TPIT Mutation. (3) | Neonatal hypoglycemia,
    hypocortisolism, and infections
22. Which mutation causes Adrenal insufficiency and disorders of sex development? | NR5A1 (SF-1)
23. What hormones are deficient in NR5A1 (SF-1) Mutation? | Gonadotropins
24. Kallmann Syndrome results from a deficiency in which hypothalamic hormone? | GnRH
25. List the key clinical features of Kallmann Syndrome (4). | Anosmia, mirror movements,
    color blindness, micropenis
26. Which hormone deficiency is central to Bardet-Biedl Syndrome? | GnRH
27. Identify the hallmark physical finding in Bardet-Biedl Syndrome. | Hexadactyly (six fingers)
28. List secondary clinical features of Bardet-Biedl Syndrome (3). | Intellectual disability, obesity,
    and blindness
29. Describe the genetic cause of Prader-Willi Syndrome. | Paternal SNRPN deletion
30. What are the clinical manifestations of Prader-Willi Syndrome? (3) | Hyperphagia, obesity, and
    muscle hypotonia
31. What mutation is most commonly linked to Kallmann Syndrome? | X-linked KAL gene
32. How is Kallmann Syndrome treated in males? (2) | hCG or testosterone
33. How is Kallmann Syndrome treated in females? | Cyclic estrogen and progestin
34. What clinical triad results from Leptin Receptor Mutations? | Hyperphagia, obesity, and
    central hypogonadism

III. ACQUIRED HYPOPITUITARISM

35. What is the most common hormone lost due to Cranial Irradiation? | GH deficiency
36. Describe the typical pattern of hormone loss after Cranial Irradiation. | GH → Gn → TSH → ACTH
37. In which patient population does Lymphocytic Hypophysitis most often occur? | Postpartum women
38. How does Lymphocytic Hypophysitis appear on imaging? | Pituitary mass resembling adenoma
39. Which inflammatory marker is elevated in Lymphocytic Hypophysitis? | ESR
40. What is the first-line medical treatment for Lymphocytic Hypophysitis? | Glucocorticoids
41. What defines Pituitary Apoplexy? | Acute hemorrhagic vascular event
42. In what setting does Pituitary Apoplexy usually occur? (2) | Pre-existing adenoma or
    postpartum (Sheehan's)
43. Why is Pituitary Apoplexy considered an endocrine emergency? | Risk of cardiovascular collapse
44. List the clinical features of Pituitary Apoplexy. (4) | Severe headache,
    meningeal irritation,
    visual changes, collapse
45. Define Empty Sella. | Sella filled with CSF
46. What is the baseline pituitary function in most cases of Empty Sella? | Usually normal
47. Which drug class includes Ipilimumab and causes hypophysitis? | CTLA-4 Inhibitors
48. What percentage of patients on CTLA-4 Inhibitors develop hypophysitis? | Up to 20%
49. Provide the specific Order of Hormone Loss in acquired pituitary failure. | GH → FSH/LH → TSH → ACTH

IV. CLINICAL FEATURES AND EVALUATION OF HORMONE DEFICIENCIES

50. What are the clinical signs of GH Deficiency in adults? (2) | Increased fat mass and
    decreased lean muscle
51. How is Secondary Hypothyroidism diagnosed via labs? | Low free T4 with
    low/normal TSH
52. Which hormone production is preserved in Secondary Adrenal Insufficiency? | Mineralocorticoids (Aldosterone)
53. What physical finding distinguishes primary from Secondary Adrenal Insufficiency? | No hyperpigmentation in secondary
54. Name the gold standard test for assessing GH and ACTH reserve. | Insulin Tolerance Test (ITT)
55. What is a normal GH response during an ITT when glucose is <40 mg/dL? | GH increase >5 µg/L
56. What peak GH response defines Adult GH Deficiency (AGHD) during ITT? | <3 µg/L
57. List three contraindications for the Insulin Tolerance Test. | Epilepsy, heart disease,
    and the elderly
58. What is the most common presenting feature of adult hypopituitarism? | Gonadotropin Deficiency
59. List symptoms associated with Gonadotropin Deficiency in adults. (3) | Loss of libido, infertility,
    and amenorrhea

V. PITUITARY ADENOMAS AND MASS EFFECTS

60. Distinguish Microadenomas from Macroadenomas by size. | Microadenomas are <1 cm
61. What size defines a Pituitary Macroadenoma? | >1 cm
62. Which visual defect is classic for Optic Chiasm Compression? | Bitemporal hemianopia
63. Describe the Stalk Section Phenomenon. | Mass blocks dopamine flow
64. What is the hormonal result of the Stalk Section Phenomenon? | Hyperprolactinemia
65. Which cranial nerves are affected by Cavernous Sinus Invasion? | III, IV, and VI
66. What are the clinical signs of Cavernous Sinus Invasion? (2) | Diplopia and ptosis
67. What is the most common pituitary hormone hypersecretion syndrome? | Prolactinoma
68. What is the surgical approach of choice for most pituitary tumors? | Transsphenoidal Surgery
69. When is Stereotactic Radiosurgery (Gamma Knife) typically utilized? | Adjunct for residual
    nonfunctioning tumors

VI. SPECIFIC HYPERSECRETORY SYNDROMES

70. What basal fasting PRL level suggests Prolactinoma? | >200 µg/L
71. Name the first-line treatment for Prolactinoma. | Dopamine Agonists (Cabergoline)
72. List the screening and confirmatory tests for Acromegaly. | Screen: Serum IGF-1
    Confirm: OGTT
73. What is the first-line treatment for Acromegaly? | Transsphenoidal Surgery
74. List three primary diagnostic tests for Cushing’s Disease. | 24-hr UFC, Midnight Cortisol,
    1-mg Dexamethasone suppression
75. What is the surgical first-line treatment for Cushing’s Disease? | Transsphenoidal Surgery
76. Describe the lab profile of a TSH Adenoma. | High T4 + Normal/High TSH
77. What is the first-line medical management for TSH Adenoma? | Surgery + Somatostatin Ligands
78. Why is Cabergoline preferred over Bromocriptine for Prolactinomas? | Higher efficacy
79. When is Bromocriptine the preferred treatment for Prolactinoma? | If pregnancy is desired
80. What GH value post-75g oral glucose load confirms Acromegaly? | GH failure to suppress <0.4 µg/L
81. List physical signs of Acromegaly. (4) | Frontal bossing, enlarged hands,
    macroglossia, Carpal tunnel
82. What is the mechanism of action of Pegvisomant? | GH receptor antagonist
83. Does Pegvisomant reduce the size of the pituitary tumor? | No
84. Which procedure distinguishes Cushing’s Disease from ectopic ACTH? | IPSS (Inferior Petrosal Sinus Sampling)
85. What IPSS CRH peak ratio confirms a pituitary source of ACTH? | ≥3
86. Define Nelson’s Syndrome. | Rapid tumor enlargement
    after bilateral adrenalectomy
87. What physical finding is characteristic of Nelson’s Syndrome? | Hyperpigmentation
88. How do Nonfunctioning Adenomas typically present? (2) | Visual loss and
    slightly elevated PRL

VII. EXPERT COMPARISONS AND DIFFERENTIATION

89. Compare TSH levels in Primary vs. Secondary Hypothyroidism. | Primary: High TSH
    Secondary: Low/Normal TSH
90. Compare pigmentation in Primary vs. Secondary Adrenal Insufficiency. | Primary: Hyperpigmentation
    Secondary: Absent
91. Compare mineralocorticoids in Primary vs. Secondary Adrenal Insufficiency. | Primary: Lost
    Secondary: Preserved
92. What extra hormones are affected in PROP-1 vs. Pit-1 mutations? | Gonadotropins (LH/FSH)
93. Compare the size of Microadenomas vs. Macroadenomas. | Micro: <1 cm
    Macro: >1 cm
94. Compare the dosing frequency of Cabergoline vs. Bromocriptine. | Cabergoline: Twice weekly
    Bromocriptine: Daily
95. Compare high-dose dexamethasone response in Pituitary Cushing’s vs. Ectopic ACTH. | Pituitary: Partial suppression
    Ectopic: Unresponsive
96. Compare SRLs (Octreotide) vs. Pegvisomant regarding GH secretion. | SRLs: Inhibit secretion
    Pegvisomant: Block receptors
97. Compare SRLs vs. Pegvisomant regarding tumor shrinkage. | SRLs: Shrink tumor
    Pegvisomant: No effect
98. Compare Kallmann vs. Bardet-Biedl regarding sensory findings. | Kallmann: Anosmia
    Bardet-Biedl: Blindness
99. Distinguish Kallmann vs. Bardet-Biedl by physical extremities. | Bardet-Biedl has polydactyly
100. Compare the site of compression in Bitemporal vs. Homonymous Hemianopia. | Bitemporal: Chiasm
     Homonymous: Post-chiasmal
101. Compare the appearance of TSH Adenoma vs. Thyroid Hormone Resistance. | Adenoma: Pituitary mass
     Resistance: No mass
102. Compare the purpose of ITT vs. Glucose Suppression Test. | ITT: Deficiency (GH/ACTH)
     Glucose: Excess (Acromegaly)
103. Compare Lymphocytic Hypophysitis vs. Pituitary Adenoma by ESR. | Hypophysitis: High ESR
     Adenoma: Normal ESR
104. Distinguish Iatrogenic Cushing’s from Cushing’s Disease. | Iatrogenic: Exogenous steroids
     Disease: Pituitary ACTH
105. What is the most common cause of Cushingoid features? | Iatrogenic Cushing's
106. What hormone is lost in Central Diabetes Insipidus? | Vasopressin (ADH)
107. Distinguish Acromegaly vs. Gigantism by timing of epiphyses closure. | Acromegaly: After closure
     Gigantism: Before closure
108. Compare the receptor affinity of Pasireotide vs. Octreotide. | Pasireotide: Higher SST5 affinity
109. What is a significant side effect of Pasireotide? | Hyperglycemia
110. Compare Stalk Effect PRL vs. Prolactinoma PRL levels. | Stalk Effect: <200 µg/L
     Prolactinoma: >250 µg/L
111. Distinguish Ketoconazole vs. Metyrapone mechanisms. | Ketoconazole: Antifungal inhibitor
     Metyrapone: 11β-hydroxylase inhibitor
112. List the components of the "3 Ps" in MEN1. | Pituitary, Parathyroid, Pancreas
113. Distinguish Prader-Willi vs. Obesity-related Hypogonadism genetically. | Prader-Willi has paternal SNRPN deletion
114. What are the neonatal features of Isolated ACTH deficiency (TPIT)? | Hypoglycemia and hypocortisolism
115. Which nuclear receptor is associated with adrenal insufficiency and sex development disorders? | SF-1 (NR5A1)
116. What visual finding is associated with Bardet-Biedl Syndrome? | Blindness by age 30
117. What is the most common cause of hyperprolactinemia in someone with a nonfunctioning macroadenoma? | Stalk effect
118. Which drug is preferred for Cushing's due to high SST5 affinity? | Pasireotide
119. What gene mutation is central to MEN1? | Menin mutation
120. Which hormone deficiency is tested when ITT results in glucose <40 mg/dL? | GH and ACTH

9

Summary

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I. POSTERIOR PITUITARY (NEUROHYPOPHYSIS) OVERVIEW

• The Posterior Pituitary blood supply terminates in a capillary plexus that drains eventually into the superior vena cava.
• Arginine Vasopressin (AVP) deficiency or action failure results in Diabetes Insipidus (DI), characterized by large volumes of dilute urine.
• Excessive AVP production results in Syndrome of Inappropriate Antidiuretic Hormone (SIADH), leading to hyponatremia and impaired water excretion.

II. ARGININE VASOPRESSIN (AVP) PHYSIOLOGY AND ACTION

• The most potent stimulus for AVP secretion is nausea, which can increase plasma AVP levels 50 to 100-fold.
• During pregnancy, the metabolic clearance of AVP increases 3-4 fold due to placental production of N-terminal peptidase.
• In the absence of AVP, principal cells remain impermeable to water, resulting in a maximum urine output of ~0.2 mL/kg/min and a specific gravity of ~1.000.
• The thirst osmostat is generally set about 3% higher than the AVP osmostat to ensure adequate fluid intake before dehydration becomes severe.

III. DIABETES INSIPIDUS (DI): ETIOLOGY AND CLINICAL FEATURES

• Diabetes Insipidus is clinically defined by a 24-hour urine volume exceeding 40 mL/kg body weight and a urine osmolarity <280 mosm/L.
• The hallmark symptoms of DI are polyuria (nocturia, enuresis) and polydipsia (excessive thirst) due to rising plasma osmolarity.
• Dipsogenic DI is a form of primary polydipsia where the thirst threshold is abnormally low, often following head trauma or neurosarcoidosis.
• In Nephrogenic DI, urine remains dilute despite high levels of circulating AVP because the kidneys cannot respond to the hormone.

IV. DIAGNOSTIC EVALUATION OF DIABETES INSIPIDUS

• A Desmopressin therapeutic trial in Primary Polydipsia eliminates polyuria but not the urge to drink, leading to severe hyponatremia within 8-24 hours.
• The Posterior Pituitary "bright spot" on T1-weighted MRI reflects stored AVP and is almost always present in Primary Polydipsia but absent in Pituitary DI.
• Hypertonic saline infusion (3% NaCl) may be used to raise plasma osmolarity to ensure accurate interpretation of AVP levels when fluid deprivation alone is insufficient.
• Copeptin is a peptide co-secreted with AVP; while stable, its baseline levels are not currently diagnostic for DI types.

V. MANAGEMENT OF DIABETES INSIPIDUS

• Desmopressin (DDAVP) is preferred over native AVP for Pituitary DI because it has 3–4× longer duration and lacks the pressor (V1) effects.
• The goal of DDAVP therapy is a target urine volume of 15–30 mL/kg/day and urine osmolarity of 400–800 mOsm/L.
• In Nephrogenic DI, Thiazides work paradoxically by inducing mild volume depletion, which increases proximal tubular reabsorption of water.
• For Pituitary DI, oral DDAVP doses (100–400 µg) are significantly higher than IV/SC doses (1–2 µg) due to low bioavailability.

VI. HYPODIPSIC HYPERNATREMIA

• Treatment of Hypodipsic Hypernatremia involves calculating the free water deficit (ΔFW) using the formula: ΔFW = 0.5 \times BW \times ([SNa - 140]/140).
• In Hypodipsic Hypernatremia, AVP secretion responds normally to non-osmotic stimuli (nausea, hypotension), confirming the neurohypophysis is intact but the osmoreceptors are not.
• When treating Hypodipsic Hypernatremia with concurrent Pituitary DI, DDAVP therapy may be required to complete rehydration.

VII. INAPPROPRIATE ANTIDIURESIS (SIADH)

• Pathophysiology of SIADH involves a slight expansion of total body water which suppresses Renin and Aldosterone, leading to modest natriuresis but no clinical edema.
• Symptoms of SIADH result from increased intracranial pressure due to cellular brain swelling as water moves into cells.
• V2-receptor antagonists (Vaptans) like Tolvaptan (oral) or Conivaptan (IV) are used to treat severe/symptomatic euvolemic hyponatremia.
• Chronic SIADH symptoms may subside after several days because the brain inactivates intracellular solutes to reduce cellular volume.

VIII. MANAGEMENT AND COMPLICATIONS OF HYPONATREMIA

• Rapid correction of hyponatremia can lead to Central Pontine Myelinolysis (Osmotic Demyelination), causing quadriparesis and ataxia.
• In NSIAD (activating V2 receptor mutation), Vaptans may fail; osmotic diuretics like Urea may be used for long-term prevention.
• Tolvaptan treatment requires close monitoring of fluid intake to avoid over-correction and resultant hypernatremia.

IX. COMPARATIVE DIFFERENTIATION OF DISORDERS

QA

1. Anatomy: Which structure is the Posterior Pituitary composed of? | Large neuronal axons. Originating in the hypothalamus.
2. Anatomy: In which hypothalamic nuclei do the axons of the Neurohypophysis originate? (2) | Supraoptic and paraventricular nuclei.
3. Hormone Storage: Where do Posterior Pituitary axons terminate? | Capillary plexus. Specifically on bulbous enlargements.
4. Hormone Storage: Where are Posterior Pituitary hormones stored before release? | Bulbous enlargements. Located on the capillary plexus.
5. Arginine Vasopressin (AVP): What is the primary renal function of AVP? | Reduces water loss. Consisted of concentrating the urine.
6. Oxytocin: What is the role of Oxytocin in the postpartum period? | Milk letdown. In response to suckling.
7. Oxytocin: What is the role of Oxytocin during labor? | Facilitates uterine contractions.
8. Anatomy: Where does the Posterior Pituitary blood supply eventually drain? | Superior vena cava. Originating from a capillary plexus.
9. Diabetes Insipidus (DI): What cause leads to Diabetes Insipidus? | AVP deficiency or action failure.
10. Diabetes Insipidus (DI): What are the urine characteristics of DI? | Large volumes of dilute urine.
11. SIADH: What results from excessive AVP production? | SIADH. Leads to hyponatremia and impaired water excretion.
12. AVP Regulation: What hypothalamic structures mediate Arginine Vasopressin (AVP) regulation? | Osmoreceptors. Located in the anteromedial hypothalamus.
13. AVP Regulation: To what specific concentration are hypothalamic osmoreceptors sensitive? | Plasma sodium concentration.
14. Secretion Threshold: At what plasma osmolarity does AVP release begin? | ~275 mosmol/L.
15. Secretion Threshold: What Sodium level corresponds to the AVP secretion threshold? | ~135 meq/L.
16. Stimuli: List five non-osmotic stimuli for AVP secretion. | 1) Volume loss 2) Nausea
    3) Hypoglycemia 4) Glucocorticoid deficiency
    5) Hyperosmolarity
17. Stimuli: What percentage of volume loss is required to stimulate AVP? | >10-20%.
18. Renal Action: To which renal receptors does Arginine Vasopressin bind? | V2 receptors.
19. Renal Action: On which surface of principal cells are V2 receptors located? | Basolateral surface.
20. Renal Action: In which specific renal segments are principal cells found? (2) | Distal tubule; medullary collecting ducts.
21. Aquaporin-2: What does V2 receptor activation trigger the insertion of? | Aquaporin-2 water channels. Inserted into the apical membrane.
22. Metabolism: What is the circulating half-life of AVP? | 10–30 minutes.
23. Metabolism: Which organs are primarily responsible for AVP clearance? (2) | Liver and kidneys.
24. Stimuli: What is the most potent stimulus for AVP secretion? | Nausea.
25. Stimuli: By how much can nausea increase plasma AVP levels? | 50 to 100-fold.
26. Pregnancy: How does pregnancy affect the metabolic clearance of AVP? | Increases 3-4 fold. Due to placental enzymes.
27. Pregnancy: Which placental enzyme degrades AVP during pregnancy? | N-terminal peptidase.
28. Absence of AVP: What is the permeability of principal cells in the absence of AVP? | Impermeable to water.
29. Absence of AVP: What is the maximum urine output in the absence of AVP? | ~0.2 mL/kg/min.
30. Absence of AVP: What is the urine specific gravity when AVP is absent? | ~1.000.
31. Thirst Osmostat: How is the thirst osmostat set relative to the AVP osmostat? | 3% higher.
32. Thirst Osmostat: Why is thirst set higher than the antidiuretic threshold? | Ensure fluid intake. Before dehydration becomes severe.
33. Pituitary DI: What is the most common type of Diabetes Insipidus? | Pituitary (Central) DI.
34. Pituitary DI: What is the primary defect in Central DI? | AVP secretion deficiency.
35. Pituitary DI: Which gene is commonly mutated in hereditary Pituitary DI? | AVP-NPII gene.
36. Nephrogenic DI: What is the primary mechanism of Nephrogenic DI? | Renal insensitivity to AVP.
37. Nephrogenic DI: What is the most common genetic form of Nephrogenic DI? | X-linked V2 receptor mutation.
38. Nephrogenic DI: List two common metabolic/drug causes of Nephrogenic DI. | Lithium and Hypokalemia.
39. Primary Polydipsia: What is the mechanism of Primary Polydipsia? | AVP suppression. Caused by excessive fluid intake.
40. Primary Polydipsia: List three categories of Primary Polydipsia. | Dipsogenic, Psychogenic, and Iatrogenic.
41. Gestational DI: What causes the transient AVP deficiency in Gestational DI? | Placental N-terminal aminopeptidase. Rapidly degrades AVP.
42. Definition: What 24-hour urine volume defines Diabetes Insipidus? | >40 mL/kg body weight.
43. Definition: What urine osmolarity defines Diabetes Insipidus? | <280 mosm/L.
44. Clinical Features: What are the two hallmark symptoms of DI? | Polyuria and polydipsia.
45. Clinical Features: How does polyuria present in Diabetes Insipidus? (2) | Nocturia and enuresis.
46. Dipsogenic DI: What is the primary defect in Dipsogenic DI? | Abnormally low thirst threshold.
47. Dipsogenic DI: In what clinical scenarios does Dipsogenic DI often occur? (2) | Head trauma; neurosarcoidosis.
48. Nephrogenic DI: Why does urine remain dilute in Nephrogenic DI despite high AVP? | Kidney non-responsiveness. Inability to respond to the hormone.
49. Diagnostic Step 1: Why is Exclusion of Glucosuria the first step in DI evaluation? | Rule out Diabetes Mellitus.
50. Diagnostic Evaluation: What does high Basal Na/Osmolarity rule out? | Primary Polydipsia.
51. Fluid Deprivation Test: What does a failure to concentrate urine after 4-6 hours suggest? | Diabetes Insipidus.
52. Desmopressin Challenge: What is the purpose of the Desmopressin Challenge? | Distinguish Pituitary vs Nephrogenic DI.
53. Desmopressin Challenge: How does Pituitary DI respond to Desmopressin? | Concentrates urine.
54. Plasma AVP: What is the gold standard test for partial DI defects? | Plasma AVP measurement.
55. Brain MRI: What does the posterior pituitary "bright spot" represent? | Stored AVP.
56. Brain MRI: What is the status of the bright spot in Pituitary DI? | Absent. Usually absent or small.
57. Therapeutic Trial: What happens when DDAVP is given to a patient with Primary Polydipsia? | Severe hyponatremia. Within 8-24 hours.
58. Therapeutic Trial: Why do patients with Primary Polydipsia develop water intoxication on DDAVP? | Urge to drink persists. While urine output is blocked.
59. Diagnostic Evaluation: When is Hypertonic saline (3% NaCl) used in DI testing? | Raise plasma osmolarity. To ensure accurate AVP interpretation.
60. Copeptin: What is Copeptin? | AVP co-secreted peptide. Stable but not currently diagnostic.
61. Pituitary DI Management: What is the first-line treatment for Pituitary DI? | Desmopressin (DDAVP).
62. Pituitary DI Management: Why is DDAVP preferred over native AVP? (2) | 1) Longer duration
    2) Lacks V1 pressor effects.
63. Nephrogenic DI Management: List four management strategies for Nephrogenic DI. | 1) Low-sodium diet 2) Thiazides
    3) Amiloride 4) Indomethacin.
64. Nephrogenic DI Management: What is the pharmacological class of Indomethacin? | Prostaglandin inhibitor.
65. Primary Polydipsia Management: What is the primary treatment? | Behavioral modification.
66. Primary Polydipsia Management: Why is DDAVP contraindicated in Primary Polydipsia? | High hyponatremia risk. Water intoxication.
67. DDAVP Therapy: What is the target urine volume goal of DDAVP treatment? | 15–30 mL/kg/day.
68. DDAVP Therapy: What is the target urine osmolarity goal in DI management? | 400–800 mOsm/L.
69. Nephrogenic DI Management: How do Thiazides paradoxically reduce polyuria? | Induce volume depletion. Increases proximal tubule reabsorption.
70. DDAVP Dosing: How do oral DDAVP doses compare to IV/SC doses? | Significantly higher. (100–400 µg vs 1–2 µg).
71. DDAVP Dosing: Why is the oral DDAVP dose much higher? | Low bioavailability.
72. Hypodipsic Hypernatremia: What is the definition of Hypodipsic Hypernatremia? | Hypertonic dehydration. Due to lack of thirst.
73. Hypodipsic Hypernatremia: Where are the destroyed osmoreceptors located? | Anterior hypothalamus.
74. Hypodipsic Hypernatremia: List four clinical signs. | 1) Tachycardia 2) Azotemia
    3) Postural hypotension 4) Hyperaldosteronism.
75. Hypodipsic Hypernatremia: What is the metabolic consequence of secondary hyperaldosteronism in this state? | Hypokalemia.
76. Hypodipsic Hypernatremia: What is the diagnostic finding in a conscious patient? | Denies thirst. Fails to drink spontaneously.
77. Free Water Deficit: Write the formula for ΔFW. | ΔFW = 0.5 × BW × ([SNa - 140]/140).
78. Hypodipsic Hypernatremia: How does AVP respond to nausea in this condition? | Responds normally. Confirms neurohypophysis is intact.
79. Hypodipsic Hypernatremia: When is DDAVP used in this condition? | Concurrent Pituitary DI. To complete rehydration.
80. SIADH: What is the core definition of SIADH? | Hypo-osmolemic hyponatremia. Inappropriate AVP secretion.
81. NSIAD: What causes Nephrogenic SIAD (NSIAD)? | Activating V2 mutations. Constantly active receptor.
82. Type I Hyponatremia: What conditions cause Hypervolemic hyponatremia? (3) | CHF, cirrhosis, or nephrosis.
83. Type I Hyponatremia: What characterizes the physical exam in Hypervolemic cases? | Generalized edema.
84. Type II Hyponatremia: What characterizes Hypovolemic hyponatremia? | Sodium/water loss. Or Addison’s disease.
85. Type II Hyponatremia: List two laboratory findings in Hypovolemic hyponatremia. | Hypotension and high PRA.
86. Type III Hyponatremia: What is Type III hyponatremia? | Euvolemic hyponatremia. Includes classic SIADH/NSIAD.
87. Pathophysiology: Why is edema absent in SIADH? | Natriuresis occurs. Suppression of Renin and Aldosterone.
88. Symptoms: What causes the symptoms in SIADH? | Brain swelling. Move water into cells from increased ICP.
89. Treatment: What are Vaptans (V2-receptor antagonists) used for? | Euvolemic hyponatremia. Severe or symptomatic.
90. Vaptans: Give two examples of Vaptans and their routes. | Tolvaptan (oral); Conivaptan (IV).
91. Chronic SIADH: Why do symptoms eventually subside in chronic SIADH? | Solute inactivation. Brain reduces its own cellular volume.
92. Management: How is Hypervolemic Hyponatremia treated? | Fluid restriction.
93. Management: Why is Hypertonic saline contraindicated in Hypervolemic Hyponatremia? | Worsens edema. And heart failure.
94. Management: How is Hypovolemic Hyponatremia replaced? | Isotonic or Hypertonic saline.
95. Management: What is contraindicated in Hypovolemic Hyponatremia? | Fluid restriction.
96. Severe Euvolemic SIADH: What is the acute treatment? | 3% Hypertonic Saline.
97. Target Rate: What is the target rate of Na rise in acute hyponatremia? | ~1% per hour.
98. Target Rate: At what Na level should acute hyponatremia treatment stop? | ~130 meq/L.
99. Complication: What is the risk of rapid sodium correction? | Osmotic Demyelination. (Central Pontine Myelinolysis).
100. Central Pontine Myelinolysis: What are the primary symptoms? (2) | Quadriparesis and ataxia.
101. NSIAD treatment: What is used if Vaptans fail in NSIAD? | Urea. An osmotic diuretic.
102. Monitoring: What must be closely monitored during Tolvaptan use? | Fluid intake. To avoid over-correction/hypernatremia.
103. Comparison: How does the Desmopressin response differ in Pituitary vs Nephrogenic DI? | Pituitary: Urine concentrates. Nephrogenic: Minimal response.
104. Comparison: How does MRI distinguish DI from Polydipsia? | Bright Spot. Present in Polydipsia; Absent in DI.
105. Comparison: What is the Natremia outcome of DDAVP in Primary Polydipsia? | Hyponatremia. (Rapidly occurs).
106. Comparison: What is the key physical finding in SIADH vs. Hypervolemic Hyponatremia? | Edema. Present in Hypervolemic; Absent in SIADH.
107. Comparison: How does Addison's differ from Secondary Adrenal Insufficiency in electrolytes? | Primary (Addison’s): High K. (Loses Aldosterone).
108. Comparison: What is the volume status in Hypodipsic hypernatremia vs Excess Salt intake? | Hypodipsia: Hypovolemia. Excess salt: Hypervolemia.
109. Comparison: How does Gestational DI differ from Central DI timing? | Gestational: Pregnancy only. Remits postpartum.
110. Comparison: How do AVP levels differ in SIADH vs NSIAD? | SIADH: Elevated AVP. NSIAD: Undetectable AVP.
111. Comparison: Which is more sensitive: AVP or Thirst? | AVP osmostat. Responds first to preserve water.
112. Comparison: How does the Thirst osmostat threshold compare to AVP? | 3% higher.
113. Comparison: What is the action of V1 receptors? | Vasoconstriction. (Pressor effect).
114. Comparison: What is the action of V2 receptors? | Water reabsorption. In the kidney.
115. Hormone Storage: What term describes the bulbous axonal enlargements in the Neurohypophysis? | Termination of axons. Store and release hormones.
116. AVP Physiology: Where are Aquaporin-2 channels specifically inserted? | Apical membrane. For water reabsorption.
117. Metabolism: How many fold can nausea increase AVP levels? | 50 to 100-fold.
118. DI Etiology: What condition is a Dipsogenic DI usually following? (1) | Head trauma. Or neurosarcoidosis.
119. Diagnostic Evaluation: What does the Posterior Pituitary "bright spot" reflect on T1-weighted MRI? | Stored Vasopressin.
120. Management: What is the target urine osmolarity for effective DDAVP therapy? | 400–800 mOsm/L.

10

Summary

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Thyroid Gland Physiology and Testing

• Thyroid Hormones: The thyroid gland produces thyroxine (T4) and triiodothyronine (T3), which act via thyroid hormone receptors (TR) α and β to maintain thermogenic and metabolic homeostasis.
• C Cells: Derived from the neural crest, C cells produce calcitonin and are the origin of medullary thyroid cancer, though they play a minimal role in human calcium homeostasis.
• Thyroid Stimulating Hormone (TSH): Secreted by anterior pituitary thyrotrope cells, TSH is the most useful physiologic marker of thyroid hormone action and exhibits a pulsatile, diurnal rhythm with peak levels at night.
• TSH Structure: TSH is a 31-kDa glycoprotein sharing an α subunit with LH, FSH, and hCG; its unique β subunit determines specificity.
• Negative Feedback: Thyroid hormones exert negative feedback on TRH and TSH primarily via the TRβ2 receptor.
• TSH Suppression: Dopamine, glucocorticoids, and somatostatin can suppress TSH levels, which is clinically relevant mainly at high doses.
• Iodine Metabolism: Iodide uptake is the rate-limiting step in thyroid hormone synthesis, mediated by the sodium-iodide symporter (NIS) on the basolateral membrane.
• NIS Regulation: NIS expression is upregulated by iodine deficiency and downregulated by iodine excess.
• Iodine Efflux: Pendrin, an iodine transporter on the apical surface, mediates iodine efflux into the lumen; mutations cause Pendred syndrome (goiter and sensorineural deafness).
• Organification and Coupling: Thyroid peroxidase (TPO) oxidizes iodide using H₂O₂ and catalyzes the coupling of MIT and DIT to produce T3 or T4.
• Wolff-Chaikoff Effect: Excess iodide transiently inhibits thyroid iodide organification.
• Cretinism: Characterized by intellectual disability and growth retardation, cretinism is typically associated with congenital hypothyroidism.
• Dietary Iodine RDA: The recommended dietary allowance for iodine is 220 μg/day for pregnancy and 290 μg/day for breastfeeding.

Thyroid Function in Pregnancy

• hCG Stimulation: During the first trimester, a transient increase in hCG weakly stimulates the TSH receptor, leading to a reciprocal fall in TSH.
• Thyroxine-Binding Globulin (TBG): Estrogen induces a rise in TBG during the 1st trimester that is sustained throughout pregnancy, increasing total T4 and T3 levels while free levels remain normal.
• Iodine Excretion in Pregnancy: Increased urinary iodide excretion and placental type III deiodinase activity can impair thyroid hormone production in areas of marginal iodine sufficiency.
• Levothyroxine in Pregnancy: Treated hypothyroid women typically require a dose increase of up to 45% during pregnancy.
• TSH Screening in Pregnancy: TSH testing is recommended for women planning pregnancy if they have a family history of autoimmune thyroid disease, type 1 diabetes, infertility, prior preterm delivery, or are older than 30.
• Free T4 in Pregnancy: Free T4 levels may slightly increase in the first trimester but decrease progressively; 3rd-trimester values may fall below nonpregnant lower limits.

Thyroid Hormone Transport and Metabolism

• T4 vs. T3 Half-life: Thyroxine (T4) has a significantly longer half-life (7 days) compared to triiodothyronine (T3) (2 days).
• Thyroid Secretion Fraction: 100% of circulating T4 is secreted directly by the thyroid, whereas only 20% of T3 is secreted by the gland; 80% of T3 comes from peripheral conversion.
• Potency: T3 is metabolically more potent and active compared to T4.
• Type I Deiodinase: Found in the thyroid, liver, and kidneys; it has a relatively low affinity for T4.
• Type II Deiodinase: Found in the pituitary, brain, and brown fat; it has a higher affinity for T4 and regulates local T3 concentrations.
• Type III Deiodinase: Expressed in the human placenta, muscle, and liver; it inactivates T4 and T3 and is the most important source of reverse T3 (rT3).
• T4 to T3 Conversion Inhibitors: Peripheral conversion is impaired by fasting, systemic illness, trauma, oral contrast, PTU, propranolol, amiodarone, and glucocorticoids.
• MCT8 and MCT10: Specific transporters that allow circulating thyroid hormones to enter cells.
• Resistance to Thyroid Hormone (RTH): An autosomal dominant disorder with elevated thyroid hormones and inappropriately normal/elevated TSH; common features include goiter, ADHD, and tachycardia.

Laboratory and Physical Evaluation

• Normal Thyroid Size: The thyroid gland normally weighs 12–20 grams and should move upon swallowing.
• Bruit/Thrill: Indicates increased vascularity and is associated with hyperthyroidism.
• Pemberton’s Sign: Venous distention over the neck and difficulty breathing when arms are raised; indicates a large retrosternal goiter.
• Biotin Interference: Biotin supplements can cause falsely low TSH and falsely high T4/T3; patients should stop biotin for at least 2 days before testing.
• TSH Sensitivity: Assays sensitive to ≤ 0.1 mIU/L are sufficient for most clinical purposes.
• Primary Hyperthyroidism Lab: Characterized by low TSH and high Free T4.
• Secondary TSH Lab: Pituitary/hypothalamic disease presents with low T4 and inappropriately low or normal TSH.
• Thyroid-Stimulating Immunoglobulins (TSI): Antibodies that stimulate the TSH receptor in Graves' disease; measured by TRAb assays.
• Serum Thyroglobulin (Tg): Tg is increased in all types of thyrotoxicosis except thyrotoxicosis factitia; it is a vital marker for thyroid cancer recurrence (target <0.20 ng/mL).
• Radioiodine Uptake (RAIU): High/homogeneous in Graves; focal in toxic adenoma; low/absent in thyroiditis and factitious thyrotoxicosis.
• "Hot" vs. "Cold" Nodules: Hot nodules (functioning) are almost never malignant; cold nodules (non-functioning) have a 5-10% malignancy risk.
• Ultrasound Malignancy Signs: Hypoechoic solid nodules with infiltrative borders and microcalcifications suggest a >90% cancer risk.

Hypothyroidism

• Hypothyroidism Symptoms: Include dry skin, nonpitting edema (myxedema), constipation, weight gain (fluid), bradycardia, and delayed tendon reflex relaxation.
• Overt Hypothyroidism: Defined by an elevated TSH (usually >10 mIU/L) and low unbound T4.
• Subclinical Hypothyroidism: Elevated TSH with normal unbound T4; treat if TSH >10, if the patient is pregnant, or wishes to conceive.
• Elderly/CAD Treatment: Start LT4 at a low dose (12.5–25 µg/day) to avoid provoking heart failure or arrhythmias.
• Secondary Hypothyroidism: Confirmed by low unbound T4 with a low or inappropriately normal TSH.
• Hashimoto’s Encephalopathy: A steroid-responsive syndrome associated with TPO antibodies, myoclonus, and slow-wave EEG activity.

Hyperthyroidism and Thyrotoxicosis

• Antithyroid Drugs (Thionamides): Methimazole is generally preferred due to its longer half-life; PTU is preferred in the first trimester of pregnancy and thyroid storm (inhibits T4 to T3 conversion).
• Radioiodine Contraindication: 131I is absolutely contraindicated in pregnancy and breastfeeding.
• Apathetic Thyrotoxicosis: Presentation in the elderly where symptoms are subtle, appearing as fatige, weight loss, and atrial fibrillation.
• SSKI (Potassium Iodide): Used pre-operatively in Graves' to reduce gland vascularity via the Wolff-Chaikoff effect.

Thyroiditis

• Acute Thyroiditis: A suppurative infection (often left-sided) usually caused by a piriform sinus remnant; thyroid function is normal, but ESR and WBC are high.
• Subacute Thyroiditis (de Quervain’s): A painful, viral-mediated inflammation with three phases (Thyrotoxic, Hypothyroid, Recovery); ESR is very high (>50) and radioiodine uptake is low (<5%).
• Subacute Thyroiditis Treatment: Large doses of aspirin or NSAIDs; glucocorticoids (Prednisone 15-40mg) if NSAIDs are inadequate.
• Silent Thyroiditis: Painless autoimmune thyroiditis; symptoms are managed with propranolol; differs from subacute by having normal ESR and (+) TPO antibodies.
• Postpartum Thyroiditis: A form of silent thyroiditis occurring 3–6 months after delivery in 5% of women; common in T1DM.
• Riedel’s Thyroiditis: A hard, fixed, "woody" goiter linked to IgG4-related disease; may require biopsy to distinguish from malignancy; tamoxifen may benefit.

Comparison / Differentiation of Key Entities

• Subacute vs. Silent Thyroiditis: Subacute thyroiditis is painful with a high ESR; Silent thyroiditis is painless with a normal ESR and (+) TPO antibodies.
• Graves’ Disease vs. Subacute Thyroiditis: Graves shows high radioiodine uptake and high T3/T4 ratio; Subacute thyroiditis shows low radioiodine uptake and a lower T3/T4 ratio (T4 is higher).
• Primary vs. Secondary Hyperthyroidism: In Primary, TSH is low and T3/T4 are high. In Secondary (pituitary tumor), both TSH and T3/T4 are high.
• Type 1 vs. Type 2 Amiodarone-Induced Thyrotoxicosis (AIT): Type 1 is hyperthyroidism (high vascularity on Doppler); Type 2 is thyroiditis (low vascularity on Doppler).
• T4 vs. T3 Half-life and Potency: T4 has a 7-day half-life and is a pro-hormone; T3 has a 2-day half-life and is the active, potent form.
• Hypothyroid vs. RTH: Hypothyroidism has high TSH and low T4; Resistance to Thyroid Hormone (RTH) has high/normal TSH and high T4.
• Sick Euthyroid vs. True Hypothyroidism: Both have low T3, but Sick Euthyroid has high reverse T3 (rT3) and usually a normal TSH, whereas Hypothyroidism has low rT3 and high TSH.
• T3 Toxicosis vs. T4 Toxicosis: T3 toxicosis (2-5% of Graves) has high T3 and normal T4. T4 toxicosis (iodine excess) has high T4 and normal T3.
• Biotin vs. Hyperthyroidism Labs: Both can show low TSH and high T4/T3. Differentiate by history of supplement use and stopping biotin for 2 days.
• Hashimoto's vs. Atrophic Thyroiditis: Hashimoto's is goitrous (firm/irregular); Atrophic is the end-stage without a palpable gland and extensive fibrosis.
• Methimazole vs. PTU: Methimazole has a longer half-life (6 hrs vs 90 min) and is once-daily. PTU is used in thyroid storm and 1st trimester pregnancy due to T4->T3 block and lower teratogenicity.
• Iodine Deficiency vs. Excess (Wolff-Chaikoff): Deficiency upregulates NIS to increase uptake; Excess transiently shuts down organification (Wolff-Chaikoff).
• Pregnancy TSH vs. Non-pregnant TSH: First trimester TSH is lower than non-pregnant due to hCG stimulation; second to third trimester usually returns to non-pregnant ranges.
• Type II vs. Type III Deiodinase: Type II converts T4 to T3 (activation); Type III converts T4/T3 into inactive forms/rT3 (inactivation).
• Pemberton’s Sign vs. NO SPECS: Pemberton’s assesses retrosternal goiter compression; NO SPECS evaluates the severity of Graves' ophthalmopathy.

QA

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Thyroid Gland Physiology and Testing

1. What receptors do Thyroid Hormones (T4 and T3) act via to maintain homeostasis? | TR α and β
2. What is the embryonic origin of C Cells? | Neural crest
3. What protein is produced by C Cells? | Calcitonin
4. From which cells does Medullary Thyroid Cancer originate? | C cells
5. What is the most useful physiologic marker of Thyroid Hormone action? | TSH
6. When do TSH levels typically reach their peak in the diurnal rhythm? | Night
7. What are the shared and unique subunits of TSH? | α (shared); β (unique)
8. Which hormones share the same α subunit as TSH? (3) | LH, FSH, and hCG
9. Through which specific receptor do thyroid hormones exert Negative Feedback on TRH and TSH? | TRβ2 receptor
10. Which substances can suppress TSH levels at high doses? (3) | Dopamine, glucocorticoids, somatostatin
11. What is the rate-limiting step in Thyroid Hormone Synthesis? | Iodide uptake
12. Which transporter on the basolateral membrane mediates Iodide Uptake? | Sodium-iodide symporter (NIS)
13. How does Iodine Deficiency affect NIS expression? | Upregulates expression
14. How does Iodine Excess affect NIS expression? | Downregulates expression
15. What apical transporter mediates Iodine Efflux into the lumen? | Pendrin
16. What are the clinical features (2) of Pendred Syndrome? | Goiter and sensorineural deafness
17. Which enzyme oxidizes iodide and catalyzes the coupling of MIT and DIT? | Thyroid peroxidase (TPO)
18. What is the Wolff-Chaikoff Effect? | Excess iodide inhibits organification
19. What are the characteristics (2) of Cretinism? | Intellectual disability; growth retardation
20. What is the RDA for Iodine during pregnancy? | 220 μg/day
21. What is the RDA for Iodine during breastfeeding? | 290 μg/day

Thyroid Function in Pregnancy

22. Why does TSH fall reciprocally during the first trimester of pregnancy? | hCG stimulates TSH-R
23. What effect does estrogen have on Thyroxine-Binding Globulin (TBG) in pregnancy? | Induces a rise
24. How do total T4/T3 levels change in pregnancy compared to Free T4/T3? | Total increases; Free normal
25. Which enzyme in the placenta can impair Thyroid Hormone production? | Type III deiodinase
26. What is the typical dose increase for Levothyroxine required during pregnancy? | Up to 45%
27. What are the criteria for TSH Screening in pregnancy? (5) | 1) Autoimmune history
    2) Type 1 Diabetes
    3) Infertility
    4) Preterm delivery
    5) Age >30
28. Describe the trend of Free T4 during the third trimester of pregnancy. | May fall below limits

Thyroid Hormone Transport and Metabolism

29. Compare the half-life of Thyroxine (T4) vs. Triiodothyronine (T3). | T4 (7 days) > T3 (2 days)
30. What percentage of circulating T4 is secreted directly by the thyroid? | 100%
31. What percentage of circulating T3 comes from peripheral conversion? | 80%
32. Which thyroid hormone is metabolically more Potent? | T3
33. Where is Type I Deiodinase primarily found? (3) | Thyroid, liver, and kidneys
34. Which deiodinase regulates local T3 concentrations in the pituitary and brain? | Type II Deiodinase
35. Which deiodinase is the most important source of reverse T3 (rT3)? | Type III Deiodinase
36. Where is Type III Deiodinase expressed? (3) | Placenta, muscle, and liver
37. What drugs/factors inhibit T4 to T3 conversion? (8) | Fasting, illness, trauma, contrast, PTU, propranolol, amiodarone, glucocorticoids
38. What are MCT8 and MCT10? | Specific thyroid hormone transporters
39. What is the inheritance pattern of Resistance to Thyroid Hormone (RTH)? | Autosomal dominant
40. What are the lab findings in Resistance to Thyroid Hormone (RTH)? | High T4; normal/high TSH
41. What are the common features (3) of Resistance to Thyroid Hormone (RTH)? | Goiter, ADHD, and tachycardia

Laboratory and Physical Evaluation

42. What is the Normal Thyroid Weight in an adult? | 12–20 grams
43. What does a Thyroid Bruit/Thrill indicate? | Increased vascularity
44. What is Pemberton’s Sign? | Venous distention upon raising arms
45. What does a positive Pemberton’s Sign indicate? | Retrosternal goiter
46. How does Biotin interfere with thyroid labs? | Low TSH; high T4/T3
47. How long should Biotin be stopped before testing? | At least 2 days
48. What lab profile defines Primary Hyperthyroidism? | Low TSH; high Free T4
49. What lab profile defines Secondary (Central) Hypothyroidism? | Low T4; low/normal TSH
50. What antibodies are measured by TRAb assays to diagnose Graves' disease? | Thyroid-Stimulating Immunoglobulins (TSI)
51. When is Serum Thyroglobulin (Tg) decreased in the setting of thyrotoxicosis? | Thyrotoxicosis factitia
52. What is the follow-up target for Thyroglobulin in thyroid cancer recurrence? | <0.20 ng/mL
53. Describe the Radioiodine Uptake (RAIU) in Graves' disease. | High and homogeneous
54. Describe the Radioiodine Uptake (RAIU) in Thyroiditis. | Low or absent
55. What is the malignancy risk of a "Hot" (functioning) Nodule? | Almost never malignant
56. What is the malignancy risk of a "Cold" Nodule? | 5-10%
57. What ultrasound signs (3) suggest Thyroid Malignancy (>90% risk)? | Hypoechoic, infiltrative borders, microcalcifications

Hypothyroidism

58. What is the incidence of Congenital Hypothyroidism? | 1:2000-4000
59. What is the #1 cause of Congenital Hypothyroidism? | Thyroid dysgenesis (65%)
60. What is the screening method for Neonatal Hypothyroidism? | Heel prick (TSH/T4)
61. What is the treatment dose for Congenital Hypothyroidism? | Levothyroxine 10-15 µg/kg/day
62. What is the most common cause of Hypothyroidism in iodine-sufficient areas? | Hashimoto's Thyroiditis
63. What are the key lab findings (2) in Hashimoto's Thyroiditis? | High TSH; (+) TPO/Tg antibodies
64. What is the standard dose and timing for Levothyroxine (LT4)? | 1.6 µg/kg; 30 min before breakfast
65. What defines Atrophic Thyroiditis? | Fibrosis and minimal residual tissue
66. What antibody-containing cells may be present in Atrophic Thyroiditis? | IgG4-positive plasma cells
67. What are the clinical signs (3) of Myxedema Coma? | Low consciousness, hypothermia, seizures
68. What is the mortality rate of Myxedema Coma? | 20-40%
69. What is the initial pharmacological treatment for Myxedema Coma? | IV LT4 + Hydrocortisone
70. What are the classic physical exam findings (4) of Hypothyroidism? | Dry skin, myxedema, bradycardia, delayed reflexes
71. What defines Overt Hypothyroidism lab-wise? | High TSH; low unbound T4
72. What defines Subclinical Hypothyroidism? | High TSH; normal unbound T4
73. When should Subclinical Hypothyroidism be treated? (3) | TSH >10, pregnant, or desiring conception
74. What is the starting dose of LT4 in the elderly or those with CAD? | 12.5–25 µg/day
75. What is Hashimoto’s Encephalopathy? | Steroid-responsive syndrome with TPO antibodies

Hyperthyroidism and Thyrotoxicosis

76. What percentage of thyrotoxicosis is caused by Graves' Disease? | 60-80%
77. What are the unique physical findings (3) of Graves' Disease? | Exophthalmos, pretibial myxedema, bruit
78. What scoring system is used for Graves' Ophthalmopathy? | NO SPECS
79. What are the life-threatening symptoms (4) of Thyroid Storm? | Fever, delirium, jaundice, heart failure
80. What is the purpose of PTU in Thyroid Storm? | Blocks T4 to T3 conversion
81. In Thyroid Storm, when should iodide be administered? | 1 hour after PTU
82. What is the characteristic appearance of Toxic Multinodular Goiter (MNG) on scan? | Multiple "hot" and "cold" areas
83. What defines Amiodarone-Induced Thyrotoxicosis (AIT) Type 1? | Jod-Basedow effect (iodine load)
84. How is AIT Type 2 distinguished from Type 1 on Doppler? | Type 2 has decreased vascularity
85. What is the treatment for AIT Type 2? | Glucocorticoids (Prednisone)
86. Why is Methimazole generally preferred over PTU? | Longer half-life (once-daily)
87. When is PTU specifically preferred over Methimazole? (2) | 1st trimester; Thyroid Storm
88. What is the absolute contraindication for Radioiodine (131I)? | Pregnancy and breastfeeding
89. What is Apathetic Thyrotoxicosis? | Subtle presentation in the elderly
90. Why is SSKI given pre-operatively in Graves'? | Reduces gland vascularity

Thyroiditis

91. What is the most common cause of Acute Thyroiditis? | Piriform sinus remnant
92. Which phase of Subacute (de Quervain’s) Thyroiditis follows the thyrotoxic phase? | Hypothyroid phase
93. What are the typical lab findings in Subacute Thyroiditis? | High ESR (>50); RAIU <5%
94. What is the first-line treatment for Subacute Thyroiditis? | Aspirin or NSAIDs
95. How does Silent Thyroiditis differ from subacute regarding labs? | Normal ESR; (+) TPO antibodies
96. When does Postpartum Thyroiditis typically occur? | 3–6 months after delivery
97. What disease is Riedel’s Thyroiditis linked to? | IgG4-related disease
98. What is the characteristic feel of the gland in Riedel’s Thyroiditis? | Hard, fixed, "woody" goiter

Comparisons and Differentiations

99. Compare Subacute vs. Silent Thyroiditis (pain and ESR). | Subacute: Painful/High ESR;
    Silent: Painless/Normal ESR
100. Compare Graves vs. Subacute Thyroiditis in terms of RAIU. | Graves: High uptake;
     Subacute: Low uptake
101. Compare Primary vs. Secondary Hyperthyroidism (TSH level). | Primary: Low TSH;
     Secondary: High TSH
102. Compare Vascularity in AIT Type 1 vs. Type 2. | Type 1: High vascularity;
     Type 2: Low vascularity
103. Compare the potency and half-life of T4 vs. T3. | T4: Longer half-life;
     T3: More potent
104. Compare Hypothyroidism vs. RTH lab profiles. | Hypothyroid: High TSH/Low T4;
     RTH: High-Normal TSH/High T4
105. How does Sick Euthyroid differ from Hypothyroidism regarding rT3? | Sick Euthyroid: High rT3;
     Hypothyroidism: Low rT3
106. What defines T3 Toxicosis lab values? | High T3; normal T4
107. How can Biotin interference be clinicaly differentiated from Hyperthyroidism? | 2-day supplement cessation
108. Compare Hashimoto's vs. Atrophic Thyroiditis exam findings. | Hashimoto's: Goiter;
     Atrophic: No palpable gland
109. Compare the mechanism of Iodine Deficiency vs. Excess on NIS. | Deficiency: Upregulates NIS;
     Excess: Downregulates NIS
110. Compare Type II vs. Type III Deiodinase function. | Type II: Activates (T4->T3);
     Type III: Inactivates
111. Contrast Pemberton's Sign vs. NO SPECS utility. | Pemberton’s: Retrosternal goiter;
     NO SPECS: Ophthalmopathy

11

Summary

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Adrenal Anatomy, Development, and Regulation

• Adrenal Cortex Layers: The adrenal cortex is organized into three zones: the outer zona glomerulosa (produces mineralocorticoids like aldosterone), the middle zona fasciculata (produces glucocorticoids like cortisol), and the inner zona reticularis (produces adrenal androgen precursors like DHEA).
• Adrenal Gland Weight: Normal adult adrenal glands weigh between 6–11 g each.
• Embryonic Origin: Adrenals originate from the urogenital ridge, separating from the gonads and kidneys at approximately the sixth week of gestation.
• Fetal Steroidogenesis: The adrenal cortex begins producing cortisol and DHEA between the seventh and ninth weeks of gestation, coinciding with sexual differentiation.
• Glucocorticoid/Androgen Regulation: Cortisol and adrenal androgens are regulated by the Hypothalamic-Pituitary-Adrenal (HPA) axis via CRH and ACTH, featuring inhibitory negative feedback.
• Mineralocorticoid Regulation: Aldosterone is primarily regulated by the Renin-Angiotensin-Aldosterone System (RAAS) and serum potassium levels, rather than the HPA axis.
• RAAS Activation: Decreased renal perfusion pressure stimulates juxtaglomerular cells to release renin, which converts angiotensinogen to angiotensin I; ACE then converts it to Angiotensin II, which triggers aldosterone secretion via the AT1 receptor.

Steroid Hormone Synthesis and Action

• Rate-Limiting Step: The transport of cholesterol into the mitochondria via the Steroidogenic Acute Regulatory (StAR) protein is the rate-limiting step in steroidogenesis.

• ACTH Signaling: ACTH binds to the MC2R receptor (requiring MRAP for trafficking), increasing cAMP and PKA to initiate steroidogenesis.

• Key Steroidogenic Enzymes Table: | Enzyme | Function | Pathway Impact | | :--- | :--- | :--- | | CYP11A1 | Side chain cleavage (Cholesterol → Pregnenolone) | All steroids | | 3β-HSD2 | Pregnenolone → Progesterone | All pathways | | CYP17A1 | 17α-hydroxylase/17,20 lyase | Cortisol and Androgens | | CYP21A2 | 21-hydroxylation | Cortisol and Aldosterone | | CYP11B1 | 11β-hydroxylation | Cortisol (Final step) | | CYP11B2 | Aldosterone synthase | Aldosterone (Final step) |

• Cortisol Transport: Cortisol circulates mostly bound to Cortisol-Binding Globulin (CBG) and albumin; only the free fraction is biologically active.

• 11β-HSD1: This enzyme converts inactive cortisone into active cortisol at the tissue level (prereceptor activation).

• 11β-HSD2: This enzyme inactivates cortisol to cortisone, primarily in the kidneys, to prevent cortisol from over-activating the mineralocorticoid receptor (MR).

• MR Affinity: Cortisol and aldosterone bind the mineralocorticoid receptor (MR) with equal affinity, but cortisol circulates at 1000-fold higher concentrations, necessitating the protective role of 11β-HSD2.

• Aldosterone Mechanism: In the kidney, aldosterone binds the MR to increase ENaC (epithelial sodium channel) expression, leading to sodium reabsorption, potassium excretion, and increased blood pressure.

Cushing’s Syndrome (Glucocorticoid Excess)

• Iatrogenic Cushing's: The most common cause overall of Cushing’s syndrome is the exogenous administration of glucocorticoids.
• Cushing’s Disease: This specific term refers to Cushing’s syndrome caused by an ACTH-producing pituitary adenoma (the most common endogenous cause).
• ACTH-Dependent etiologies: Includes Pituitary adenomas (75-80%) and Ectopic ACTH secretion (e.g., from bronchial or pancreatic carcinoids).
• ACTH-Independent etiologies: Includes Adrenocortical adenomas, carcinomas, or nodular hyperplasia; characterized by suppressed plasma ACTH.
• Clinical Manifestations: Classic features include central obesity, buffalo hump, moon facies, broad purple striae (>1 cm), easy bruising, proximal myopathy, and psychiatric symptoms (anxiety/depression).
• Hypokalemia in Cushing's: Severe cortisol excess can overwhelm the 11β-HSD2 enzyme, leading to mineralocorticoid effects like diastolic hypertension and hypokalemia (common in ectopic ACTH).
• Screening Tests: Diagnosis requires increased 24-hour urinary free cortisol (UFC) (3 collections), failure of Overnight Dexamethasone Suppression Test (1mg), or loss of diurnal rhythm (high midnight salivary/serum cortisol).
• Differentiating Etiology: High-dose dexamethasone suppresses ACTH in Cushing's Disease but not in Ectopic ACTH or adrenal tumors.
• Inferior Petrosal Sinus Sampling (IPSS): The gold standard for distinguishing Cushing’s Disease from Ectopic ACTH when biochemical tests are inconclusive; a central-to-peripheral ACTH ratio >2 (baseline) or >3 (post-CRH) confirms a pituitary source.
• Surgical Treatment: Transsphenoidal surgery is the first-line for Cushing’s Disease; unilateral adrenalectomy for adrenal adenomas.
• Medical Management: Drugs like Metyrapone, Ketoconazole, and Osilodrostat (11β-hydroxylase inhibitors) are used to control cortisol synthesis.
• Adrenal Crisis Prevention: Patients require glucocorticoid replacement therapy immediately following the removal of a cortisol-secreting tumor because the remaining HPA axis is chronically suppressed.

Mineralocorticoid Excess (Hyperaldosteronism)

• Conn's Syndrome: An aldosterone-producing adrenal adenoma causing primary hyperaldosteronism.
• Primary Aldosteronism (PA): The most common cause of mineralocorticoid excess; typically caused by bilateral micronodular hyperplasia or unilateral adenomas.
• Glucocorticoid-Remediable Aldosteronism (GRA): An autosomal dominant condition where a chimeric gene makes aldosterone synthesis ACTH-dependent; treated with low-dose dexamethasone.
• Liddle’s Syndrome: A genetic "pseudoaldosteronism" caused by constitutively active ENaC; manifests with hypertension and hypokalemia but low aldosterone; treated with Amiloride.
• Clinical Hallmarks: Hypokalemic hypertension, metabolic alkalosis, and increased cardiac remodeling. Note: 50% of PA patients may have normal potassium.
• Screening (ARR): The Aldosterone-Renin Ratio (ARR) is the screening test of choice. ARR >750 pmol/L per ng/mL/h with high aldosterone is positive.
• Medication Interference: MR antagonists (Spironolactone) must be stopped 4 weeks prior to ARR testing. Beta-blockers cause false positives; ACE inhibitors/ARBs cause false negatives.
• Confirmatory Tests: Saline Infusion Test (failure of aldosterone to suppress <140 pmol/L) or Oral Sodium Loading.
• Adrenal Vein Sampling (AVS): Necessary in surgical candidates >40 years to distinguish unilateral adenoma (curable by surgery) from bilateral hyperplasia (treated medically). Lateralization is confirmed by an aldosterone/cortisol ratio 2x higher than the other side.
• Medical Treatment: Spironolactone is the first-line MR antagonist; Eplerenone is a more selective alternative to avoid side effects like gynecomastia.

Adrenal Masses and Carcinoma

• Adrenal Incidentaloma: An incidentally discovered mass >1 cm requires evaluation for hormone autonomy and malignancy risk.
• Imaging Characteristics: Adrenal CT density <10–20 Hounsfield Units (HU) suggests a lipid-rich benign adenoma. Malignant lesions are usually larger (>4 cm), inhomogeneous, and lobulated.
• Adrenocortical Carcinoma (ACC): A rare, highly aggressive malignancy; often presents with mixed hormone excess (cortisol + androgens). IGF2 overexpression is found in 90% of cases.

Adrenal Insufficiency (Hypoadrenalism)

• Primary Adrenal Insufficiency (Addison’s Disease): Caused by destruction of the gland (most commonly autoimmune adrenalitis). It involves the loss of both glucocorticoids and mineralocorticoids.
• Secondary Adrenal Insufficiency: Caused by HPA axis dysfunction (pituitary/hypothalamic tumors or iatrogenic steroid suppression). Mineralocorticoid secretion is preserved as it is regulated by RAAS.
• Hyperpigmentation: A hallmark of Primary AI due to high ACTH levels stimulating melanocytes; found in skin creases, nipples, and oral mucosa.
• Adrenal Crisis: An acute, life-threatening emergency presenting with hypotension/shock, abdominal pain, fever, and vomiting; often triggered by stress or infection.
• Diagnostic Gold Standard: The Short Cosyntropin (ACTH) Test. A peak cortisol <450–500 nmol/L at 30–60 mins indicates insufficiency.
• Differentiating Primary vs. Secondary: High ACTH + High Renin = Primary; Low/Normal ACTH = Secondary.
• Acute Treatment: Immediate IV saline rehydration + IV Hydrocortisone (100 mg bolus, then 200 mg/24h).
• Chronic Maintenance: Oral Hydrocortisone (15–25 mg in divided doses). Mineralocorticoid replacement (Fludrocortisone) is only required for Primary AI.
• Steroid Equipotency: 1 mg Hydrocortisone = 0.2 mg Prednisolone = 0.25 mg Prednisone = 0.025 mg Dexamethasone.

Congenital Adrenal Hyperplasia (CAH)

• 21-Hydroxylase Deficiency: Accounts for 90–95% of CAH cases; leads to low cortisol (causing high ACTH and adrenal hyperplasia) and high androgens.
• Classic CAH: Presents in neonates; girls have ambiguous genitalia (virilization). Salt-wasting form includes mineralocorticoid deficiency, risking adrenal crisis.
• Diagnosis: Elevated 17-hydroxyprogesterone (17OHP) levels.
• Treatment Goals: Replace cortisol to suppress ACTH and reduce excessive androgen production.

Pheochromocytoma and Paraganglioma (PPGL)

• Pheochromocytoma Locations: Pheochromocytomas arise from the adrenal medulla; Paragangliomas arise from extra-adrenal sympathetic or parasympathetic ganglia.
• Rule of 10s (Classic): 10% are bilateral, 10% are extra-adrenal, and 10% are metastatic (though move toward a genetic-based classification is modern).
• Classic Triad: 1) Episodic headache, 2) Palpitations/tachycardia, and 3) Diaphoresis.
• Biochemical Testing: Plasma and 24-hour urinary fractionated metanephrines are the most reliable markers (more sensitive than catecholamines).
• Clonidine Suppression Test: Used if metanephrines are equivocal; clonidine fails to suppress normetanephrine in patients with pheochromocytoma.
• Histology: Characteristic Zellballen pattern (nests of chief cells). Chief cells stain for Chromogranin/Synaptophysin; sustentacular cells stain for S-100.
• Pre-operative Management: Alpha-blockade FIRST (e.g., Phenoxybenzamine) for 7–14 days, followed by beta-blockers only after adequate alpha-blockade to avoid a hypertensive crisis (unopposed alpha-stimulation).
• Pregnancy Management: Tumor removal is best performed in the fourth to sixth month of gestation.

Multiple Endocrine Neoplasia (MEN) Syndromes

• MEN 1 (Wermer’s): Triad of 3 Ps: Parathyroid (90%, hyperplasia/adenoma), Pancreatic NETs (e.g., Gastrinoma, Insulinoma), and Anterior Pituitary adenomas (e.g., Prolactinoma). Gene: MEN1 (Menin).
• Zollinger-Ellison Syndrome (ZES): Often caused by gastrinomas in MEN 1; presents with severe, recurrent peptic ulcers.
• MEN 2A (Sipple’s): Defined by Medullary Thyroid Carcinoma (MTC) (100%), Pheochromocytoma (50%), and Parathyroid hyperplasia (20%). Gene: RET (proto-oncogene).
• MEN 2B (MEN 3): Defined by aggressive MTC, Pheochromocytoma, mucosal neuromas (lips/tongue), and Marfanoid habitus. Note: No parathyroid disease. Gene: RET (specific codon 918 mutation).
• MEN 4: MEN 1-like phenotype but caused by mutations in CDKN1B (p27).
• Medullary Thyroid Carcinoma (MTC): Screening via Serum Calcitonin. Management involves prophylactic total thyroidectomy in RET-positive infants/children.
• Carney Complex: Spotty skin pigmentation, cardiac myxomas, and PPNAD (periodic Cushing syndrome). Gene: PRKAR1A.
• McCune-Albright Syndrome: Triad of polyostotic fibrous dysplasia, café-au-lait spots, and precocious puberty. Caused by a postzygotic GNAS mutation (mosaicism).

Differential Diagnosis and Critical Comparisons

• Cushing Disease vs. Ectopic ACTH: Cushing Disease (pituitary) usually shows suppression with high-dose dexamethasone and response to CRH; Ectopic ACTH shows neither and presents with very high ACTH and severe hypokalemia.
• Primary vs. Secondary Adrenal Insufficiency: Primary (Addison’s) has hyperpigmentation and hyperkalemia (due to mineralocorticoid loss). Secondary has "alabaster" pale skin and normal potassium (intact mineralocorticoid axis).
• Primary vs. Secondary Aldosteronism: Primary Aldosteronism has Low Renin (suppressed by high aldosterone). Secondary Aldosteronism (e.g., renal artery stenosis) has High Renin driving the aldosterone.
• PA vs. Liddle’s Syndrome: Both present with hypokalemic hypertension. PA has high aldosterone/low renin; Liddle’s has Low Aldosterone/Low Renin.
• MEN 2A vs. MEN 2B: Both have MTC and Pheo. MEN 2A has Hyperparathyroidism; MEN 2B has Neuromas/Marfanoid habitus and no parathyroid disease.
• 11β-HSD1 vs. 11β-HSD2: 11β-HSD1 activates (cortisone → cortisol) in many tissues. 11β-HSD2 inactivates (cortisol → cortisone) in the kidney to protect the MR.
• Hypokalemia in Cushing's vs. PA: In PA, it's due to direct aldosterone action. In Cushing’s, it's due to excess cortisol overwhelming 11β-HSD2, activating the MR.
• Adrenal Adenoma vs. Carcinoma: Adenomas are 1–2 cm, homogenous, and low HU (<10–20). Carcinomas are >4 cm, inhomogeneous, and often secrete multiple steroids (Cortisol + Androgens).
• Spironolactone vs. Eplerenone: Spironolactone is a non-selective MR antagonist (causes gynecomastia). Eplerenone is selective and bypasses androgen/progesterone receptor interference.
• Primary vs. Secondary AI Potassium: Hyperkalemia is a clue for Primary AI. Normal potassium is typical for Secondary AI.
• ACTH in AI: ACTH is high in Primary AI (distinguishing skin darkening) and low/normal in Secondary AI.
• Cushing Screening Interference: Biotin (interferes with assays); Estrogens/OCPs (elevate CBG, false positive Dexamethasone test); Antiepileptics (accelerate Dex metabolism).
• Pheo vs. Anxiety: Pheochromocytoma paroxysms are usually shorter (<1 hr) and accompanied by significant hypertension, unlike standard panic attacks.
• MEN 1 vs. MEN 4: Phenotypically identical, but MEN 1 involves the menin protein; MEN 4 involves the p27 cell cycle inhibitor.
• Adrenal CT: Benign vs. Malignant: Benign density is <20 HU; Malignant density is >20 HU and shows slow "washout" of contrast.

QA

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Adrenal Anatomy, Development, and Regulation

1. List the three layers of the Adrenal Cortex from outer to inner. | 1) Zona glomerulosa
   2) Zona fasciculata
   3) Zona reticularis
2. What is the primary steroid produced by the Zona Glomerulosa? | Mineralocorticoids (Aldosterone)
3. What is the primary steroid produced by the Zona Fasciculata? | Glucocorticoids (Cortisol)
4. What is the primary steroid produced by the Zona Reticularis? | Adrenal androgen precursors (DHEA)
5. What is the normal weight of a single Adult Adrenal Gland? | 6–11 g
6. From which embryonic structure do the Adrenal Glands originate? | Urogenital ridge
7. At what gestational week do the Adrenals separate from the gonads and kidneys? | Sixth week
8. When does Fetal Steroidogenesis of cortisol and DHEA begin? | Seventh to ninth weeks
9. Which axis regulates Cortisol and Adrenal Androgens? | Hypothalamic-Pituitary-Adrenal (HPA) axis
10. Which hormones from the hypothalamus and pituitary regulate the HPA axis? | CRH and ACTH
11. What are the primary regulators of Aldosterone secretion? (2) | 1) RAAS (Renin-Angiotensin-Aldosterone System)
    2) Serum potassium levels
12. Does the HPA Axis primarily regulate mineralocorticoid secretion? | No. It is primarily regulated by RAAS and potassium.
13. Which cells release Renin in response to decreased renal perfusion? | Juxtaglomerular cells
14. What enzyme converts Angiotensin I to Angiotensin II? | ACE (Angiotensin-Converting Enzyme)
15. Which receptor does Angiotensin II bind to trigger aldosterone secretion? | AT1 receptor

Steroid Hormone Synthesis and Action

16. What is the Rate-Limiting Step in steroidogenesis? | Transport of cholesterol into mitochondria
17. Which protein facilitates the Rate-Limiting Step of steroidogenesis? | StAR protein (Steroidogenic Acute Regulatory)
18. To which receptor does ACTH bind in the adrenal cortex? | MC2R receptor
19. Which accessory protein is required for MC2R trafficking? | MRAP
20. What second messengers are increased by ACTH Signaling? | cAMP and PKA
21. What is the function of the enzyme CYP11A1? | Side chain cleavage (Cholesterol to Pregnenolone)
22. Which enzyme converts Pregnenolone to Progesterone? | 3β-HSD2
23. What is the dual function of the enzyme CYP17A1? | 17α-hydroxylase and 17,20 lyase
24. Which enzyme performs 21-hydroxylation for cortisol and aldosterone? | CYP21A2
25. Which enzyme catalyzes the final step of Cortisol synthesis? | CYP11B1 (11β-hydroxylation)
26. Which enzyme (aldosterone synthase) catalyzes the final step of Aldosterone synthesis? | CYP11B2
27. To which proteins does Cortisol mostly bind in circulation? (2) | 1) Cortisol-Binding Globulin (CBG)
    2) Albumin
28. Which fraction of Circulating Cortisol is biologically active? | Free fraction
29. What is the function of the enzyme 11β-HSD1? | Converts inactive cortisone to active cortisol
30. Where is 11β-HSD2 primarily located? | Kidneys
31. What is the function of 11β-HSD2 in the kidney? | Inactivates cortisol to cortisone
32. Why is 11β-HSD2 necessary for the mineralocorticoid receptor (MR)? | Prevents cortisol from over-activating MR
33. Compare the affinity of Cortisol vs. Aldosterone for the Mineralocorticoid Receptor (MR). | They have equal affinity
34. How much higher is the circulating concentration of Cortisol compared to aldosterone? | 1000-fold higher
35. What channel expression is increased by Aldosterone in the kidney? | ENaC (epithelial sodium channel)
36. What are the physiological effects of Aldosterone on electrolytes and BP? (3) | 1) Sodium reabsorption
    2) Potassium excretion
    3) Increased blood pressure

Cushing’s Syndrome (Glucocorticoid Excess)

37. What is the Most Common Cause Overall of Cushing’s syndrome? | Exogenous glucocorticoid administration (Iatrogenic)
38. Define the term Cushing’s Disease. | ACTH-producing pituitary adenoma
39. What are the ACTH-Dependent etiologies of Cushing's? (2) | 1) Pituitary adenomas
    2) Ectopic ACTH secretion
40. What are common sources of Ectopic ACTH? | Bronchial or pancreatic carcinoids
41. What characterizes ACTH-Independent Cushing's syndrome? | Suppressed plasma ACTH
42. List the common ACTH-Independent etiologies of Cushing's. (3) | Adrenocortical adenomas, carcinomas, or nodular hyperplasia
43. List the classic clinical manifestations of Cushing’s Syndrome. (6) | 1) Central obesity
    2) Buffalo hump
    3) Moon facies
    4) Purple striae
    5) Easy bruising
    6) Proximal myopathy
44. What defines Purple Striae in Cushing's syndrome? | Breadth greater than 1 cm
45. Why does Severe Cortisol Excess cause hypokalemia? | Overwhelms 11β-HSD2; activates mineralocorticoid receptors
46. Which etiology of Cushing's is most associated with Hypokalemia and Diastolic Hypertension? | Ectopic ACTH secretion
47. What are the recommended Screening Tests for Cushing’s syndrome? (3) | 1) 24-hour UFC
    2) Overnight Dexamethasone Suppression
    3) Midnight salivary/serum cortisol
48. How many 24-hour Urinary Free Cortisol (UFC) collections are typically required? | Three collections
49. How does High-Dose Dexamethasone affect ACTH in Cushing's Disease vs. Ectopic ACTH? | Suppresses in Cushing's Disease; no effect in Ectopic ACTH
50. What is the gold standard for distinguishing Cushing’s Disease from Ectopic ACTH? | Inferior Petrosal Sinus Sampling (IPSS)
51. What IPSS Central-to-Peripheral ACTH Ratio confirms a pituitary source? | >2 at baseline or >3 post-CRH
52. What is the first-line treatment for Cushing’s Disease? | Transsphenoidal surgery
53. What is the treatment for Unilateral Adrenal Adenoma causing Cushing's? | Unilateral adrenalectomy
54. Name three 11β-Hydroxylase Inhibitors used for medical management of Cushing's. | 1) Metyrapone
    2) Ketoconazole
    3) Osilodrostat
55. Why is Glucocorticoid Replacement needed after removing a cortisol-secreting tumor? | Remaining HPA axis is chronically suppressed

Mineralocorticoid Excess (Hyperaldosteronism)

56. Define Conn's Syndrome. | Aldosterone-producing adrenal adenoma
57. What is the Most Common Cause of mineralocorticoid excess? | Primary Aldosteronism (PA)
58. What are the two main causes of Primary Aldosteronism? | 1) Bilateral micronodular hyperplasia
    2) Unilateral adenomas
59. What is the genetic mechanism of Glucocorticoid-Remediable Aldosteronism (GRA)? | Chimeric gene makes aldosterone synthesis ACTH-dependent
60. How is Glucocorticoid-Remediable Aldosteronism (GRA) treated? | Low-dose dexamethasone
61. What is the cause of Liddle’s Syndrome? | Constitutively active ENaC (genetic)
62. Describe the Aldosterone and Renin levels in Liddle’s Syndrome. | Both low (Pseudoaldosteronism)
63. What is the treatment for Liddle’s Syndrome? | Amiloride
64. List the Clinical Hallmarks of Primary Aldosteronism. (3) | 1) Hypokalemic hypertension
    2) Metabolic alkalosis
    3) Cardiac remodeling
65. What percentage of patients with Primary Aldosteronism have normal potassium? | 50 percent
66. What is the screening test of choice for Primary Aldosteronism? | Aldosterone-Renin Ratio (ARR)
67. What ARR Value is considered positive for Primary Aldosteronism? | >750 pmol/L per ng/mL/h
68. How long must MR Antagonists be stopped before ARR testing? | Four weeks
69. How do Beta-Blockers affect ARR testing? | Cause false positives
70. How do ACE inhibitors and ARBs affect ARR testing? | Cause false negatives
71. List two Confirmatory Tests for Primary Aldosteronism. | 1) Saline Infusion Test
    2) Oral Sodium Loading
72. What result in the Saline Infusion Test confirms Primary Aldosteronism? | Failure of aldosterone to suppress <140 pmol/L
73. When is Adrenal Vein Sampling (AVS) necessary? | Surgical candidates >40 years old
74. What AVS Ratio confirms lateralization in Primary Aldosteronism? | Aldosterone/cortisol ratio 2x higher than other side
75. Which Mineralocorticoid Receptor Antagonist is first-line for medical treatment of PA? | Spironolactone
76. Why is Eplerenone preferred over spironolactone in some patients? | Selective; avoids side effects like gynecomastia

Adrenal Masses and Carcinoma

77. What size threshold defines an Adrenal Incidentaloma? | Greater than 1 cm
78. What CT density in Hounsfield Units (HU) suggests a benign adenoma? | <10–20 HU
79. What are the imaging characteristics of Malignant Adrenal Lesions? (3) | 1) >4 cm
    2) Inhomogeneous
    3) Lobulated
80. How does Adrenocortical Carcinoma (ACC) often present hormonal-wise? | Mixed hormone excess (Cortisol + Androgens)
81. Which factor is overexpressed in 90% of ACC cases? | IGF2

Adrenal Insufficiency (Hypoadrenalism)

82. What is the most common cause of Primary Adrenal Insufficiency? | Autoimmune adrenalitis (Addison’s Disease)
83. Which hormones are lost in Primary Adrenal Insufficiency? | Both glucocorticoids and mineralocorticoids
84. What causes Secondary Adrenal Insufficiency? | HPA axis dysfunction (tumors or steroid suppression)
85. Why is Mineralocorticoid Secretion preserved in secondary AI? | Regulated by RAAS, not the pituitary
86. Why does Hyperpigmentation occur in Primary AI? | High ACTH levels stimulate melanocytes
87. Where is Hyperpigmentation classically found in Addison’s? (3) | 1) Skin creases
    2) Nipples
    3) Oral mucosa
88. List the clinical presentation of an Adrenal Crisis. (4) | 1) Hypotension/shock
    2) Abdominal pain
    3) Fever
    4) Vomiting
89. What is the diagnostic gold standard for Adrenal Insufficiency? | Short Cosyntropin (ACTH) Test
90. What peak cortisol value indicates AI in a Short Cosyntropin Test? | <450–500 nmol/L at 30–60 mins
91. Compare ACTH and Renin in Primary vs. Secondary AI. | Primary: High ACTH + High Renin; Secondary: Low/Normal ACTH
92. What is the Acute Treatment for an Adrenal Crisis? | IV saline rehydration + IV Hydrocortisone (100 mg bolus)
93. What is the Chronic Maintenance dose for Oral Hydrocortisone? | 15–25 mg in divided doses
94. Which type of AI requires Fludrocortisone replacement? | Primary Adrenal Insufficiency only
95. 1 mg of Hydrocortisone is equivalent to how much Prednisolone? | 0.2 mg
96. 1 mg of Hydrocortisone is equivalent to how much Dexamethasone? | 0.025 mg

Congenital Adrenal Hyperplasia (CAH)

97. What enzyme deficiency causes 90-95% of CAH cases? | 21-Hydroxylase Deficiency
98. What are the hormonal results of 21-Hydroxylase Deficiency? | Low cortisol and High androgens
99. How does Classic CAH present in newborn girls? | Ambiguous genitalia (virilization)
100. What additional deficiency is found in the Salt-Wasting Form of CAH? | Mineralocorticoid deficiency
101. What is the primary diagnostic marker for CAH? | Elevated 17-hydroxyprogesterone (17OHP)
102. What are the main Treatment Goals for CAH? | Replace cortisol to suppress ACTH and reduce androgens

Pheochromocytoma and Paraganglioma (PPGL)

103. Where do Pheochromocytomas arise? | Adrenal medulla
104. Where do Paragangliomas arise? | Extra-adrenal sympathetic or parasympathetic ganglia
105. State the Rule of 10s for pheochromocytoma. (3) | 1) 10% bilateral
     2) 10% extra-adrenal
     3) 10% metastatic
106. List the Classic Triad of pheochromocytoma symptoms. | 1) Episodic headache
     2) Palpitations
     3) Diaphoresis
107. Which biochemical tests are most reliable for PPGL? | Plasma and 24-hour urinary fractionated metanephrines
108. When is a Clonidine Suppression Test used? | If metanephrines are equivocal
109. Describe the characteristic Histology of pheochromocytoma. | Zellballen pattern (nests of chief cells)
110. What do Chief Cells and Sustentacular Cells stain for in PPGL? | Chief: Chromogranin/Synaptophysin; Sustentacular: S-100
111. What is the correct Pre-operative Sequence for PPGL? | Alpha-blockade first, then Beta-blockers
112. Why must Alpha-blockade precede beta-blockade in PPGL? | To avoid hypertensive crisis from unopposed alpha-stimulation
113. When is the best time for PPGL Tumor Removal during pregnancy? | Fourth to sixth month of gestation

Multiple Endocrine Neoplasia (MEN) Syndromes

114. List the 3 Ps of MEN 1 (Wermer’s). | 1) Parathyroid
     2) Pancreatic NETs
     3) Anterior Pituitary
115. Which gene is mutated in MEN 1? | MEN1 (Menin)
116. What syndrome causes recurrent peptic ulcers in MEN 1? | Zollinger-Ellison Syndrome (Gastrinoma)
117. List the components of MEN 2A (Sipple’s). (3) | 1) Medullary Thyroid Carcinoma
     2) Pheochromocytoma
     3) Parathyroid hyperplasia
118. Which gene/protein is mutated in MEN 2 (A and B)? | RET (proto-oncogene)
119. List the components of MEN 2B. (4) | 1) Aggressive MTC
     2) Pheo
     3) Mucosal neuromas
     4) Marfanoid habitus
120. Is Parathyroid Disease present in MEN 2B? | No
121. What gene is mutated in MEN 4? | CDKN1B (p27)
122. How is Medullary Thyroid Carcinoma (MTC) screened? | Serum Calcitonin
123. Define Carney Complex findings. | Spotty pigmentation, cardiac myxomas, PPNAD
124. What are the three components of McCune-Albright Syndrome? | Polyostotic fibrous dysplasia, café-au-lait spots, precocious puberty
125. What is the genetic cause of McCune-Albright Syndrome? | Postzygotic GNAS mutation (mosaicism)

Differential Diagnosis and Critical Comparisons

126. Contrast Cushing Disease vs. Ectopic ACTH response to High-dose Dex. | Disease: Suppresses; Ectopic: No suppression
127. Contrast Primary vs. Secondary AI skin color. | Primary: Hyperpigmentation; Secondary: "Alabaster" pale skin
128. Contrast Primary vs. Secondary Aldosteronism renin levels. | Primary: Low Renin; Secondary: High Renin
129. How do you distinguish Primary Aldosteronism from Liddle’s Syndrome? | PA: High Aldosterone; Liddle’s: Low Aldosterone
130. Contrast 11β-HSD1 vs. 11β-HSD2 function. | 11β-HSD1: Activates (cortisone to cortisol); 11β-HSD2: Inactivates (cortisol to cortisone)
131. Contrast Adrenal Adenoma vs. Carcinoma size and HU. | Adenoma: 1-2 cm, homogenous, <20 HU; Carcinoma: >4 cm, inhomogeneous, >20 HU
132. Compare Primary vs. Secondary AI potassium levels. | Primary: Hyperkalemia; Secondary: Normal potassium
133. Contrast Pheochromocytoma Paroxysms with Panic Attacks. | Pheo: shorter (<1 hr) with significant hypertension
134. Contrast MEN 1 vs. MEN 4 protein involvement. | MEN 1: menin; MEN 4: p27 cell cycle inhibitor
135. Contrast Benign vs. Malignant Adrenal CT Washout. | Benign: Fast washout; Malignant: Slow washout

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Summary

QA