ITE Endocrinology 3 — Questions and Answers
Question 1: A 28-year-old woman with Graves' disease is in her first trimester of pregnancy. Which antithyroid drug is preferred during this period?
- Methimazole
- Propylthiouracil (PTU) (Correct answer)
- Radioactive iodine
- Potassium iodide
Correct answer: Propylthiouracil (PTU)
PTU is preferred in the first trimester because methimazole is associated with embryopathy (aplasia cutis, choanal atresia) during organogenesis.
Question 2: Which of the following is the most specific marker for differentiating central from nephrogenic diabetes insipidus?
- Serum sodium level
- Response to desmopressin (DDAVP) administration (Correct answer)
- 24-hour urine volume
- Urine specific gravity at baseline
Correct answer: Response to desmopressin (DDAVP) administration
Patients with central DI show significant increase in urine osmolality after DDAVP, while those with nephrogenic DI do not respond.
Question 3: A 60-year-old man has a random serum cortisol of 3 mcg/dL after an overnight dexamethasone suppression test. What is the next best step?
- Proceed with bilateral adrenalectomy
- Repeat the overnight dexamethasone suppression test
- Perform 24-hour urinary free cortisol and late-night salivary cortisol (Correct answer)
- Obtain pituitary MRI immediately
Correct answer: Perform 24-hour urinary free cortisol and late-night salivary cortisol
A cortisol >1.8 mcg/dL after overnight dexamethasone suppression is a positive screen, and confirmatory testing (24h UFC and late-night salivary cortisol) should follow.
Question 4: An elderly patient on long-term lithium therapy presents with polyuria and polydipsia. Urine osmolality remains low after water restriction but does not improve after DDAVP. What is the mechanism?
- Lithium stimulates excessive ADH secretion
- Lithium blocks aquaporin-2 insertion in collecting ducts causing nephrogenic DI (Correct answer)
- Lithium causes central DI by damaging the posterior pituitary
- Lithium increases renal glucose reabsorption
Correct answer: Lithium blocks aquaporin-2 insertion in collecting ducts causing nephrogenic DI
Lithium causes nephrogenic DI by inhibiting the response of collecting duct principal cells to ADH, impairing aquaporin-2 trafficking.
Question 5: A patient with MEN1 syndrome is found to have a gastrinoma. Which finding would be expected?
- Hypocalcemia and low PTH
- Elevated fasting serum gastrin with acid hypersecretion (Correct answer)
- Suppressed insulin levels with hypoglycemia
- Low VIP levels with watery diarrhea
Correct answer: Elevated fasting serum gastrin with acid hypersecretion
Gastrinomas cause Zollinger-Ellison syndrome, characterized by elevated fasting gastrin (>1000 pg/mL) and recurrent peptic ulcers from gastric acid hypersecretion.
Question 6: Which HbA1c target is most appropriate for a 78-year-old patient with type 2 diabetes, multiple comorbidities, and limited life expectancy?
- <6.5%
- <7.0%
- <8.0% (Correct answer)
- <9.0%
Correct answer: <8.0%
ADA guidelines recommend a less stringent HbA1c target of <8.0% for older patients with complex health status to minimize hypoglycemia risk without benefit.
Question 7: A patient with chronic hyponatremia is treated with hypertonic saline. Sodium corrects rapidly from 112 to 132 mEq/L over 24 hours. What is the most feared complication?
- Cerebral edema
- Osmotic demyelination syndrome (Correct answer)
- Central DI
- Hypertensive emergency
Correct answer: Osmotic demyelination syndrome
Overly rapid correction of chronic hyponatremia (>10–12 mEq/L/24h) causes osmotic demyelination syndrome (central pontine myelinolysis).
ITE Endocrinology 3
A 28-year-old woman with Graves' disease is in her first trimester of pregnancy.
Which antithyroid drug is preferred during this period?