ITE Endocrinology 3

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?

Accepted Answer

Propylthiouracil (PTU)

Answer

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?

Accepted Answer

Response to desmopressin (DDAVP) administration

Answer

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?

Accepted Answer

Perform 24-hour urinary free cortisol and late-night salivary cortisol

Answer

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?

Accepted Answer

Lithium blocks aquaporin-2 insertion in collecting ducts causing nephrogenic DI

Answer

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?

Accepted Answer

Elevated fasting serum gastrin with acid hypersecretion

Answer

Gastrinomas cause Zollinger-Ellison syndrome, characterized by elevated fasting gastrin (>1000 pg/mL) and recurrent peptic ulcers from gastric acid hypersecretion.

ITE - Internal Medicine In-Training Exam Practice Test

ITE - Internal Medicine In-Training Exam Practice Test

ITE Endocrinology 3