ITE Endocrinology and Metabolism 4

Question 1

A 30-year-old man presents with polyuria, polydipsia, and a serum sodium of 148 mEq/L. Urine osmolality is 110 mOsm/kg after water deprivation, rising to 680 mOsm/kg after desmopressin (DDAVP). What is the diagnosis?

Accepted Answer

Central (neurogenic) diabetes insipidus

Answer

A markedly concentrated urine response to exogenous DDAVP after failure to concentrate with water deprivation indicates central diabetes insipidus, where ADH is deficient but the kidney can respond normally.

Question 2

A 58-year-old woman on long-term lithium therapy presents with fatigue and a calcium of 10.8 mg/dL. PTH is 72 pg/mL (high-normal). What is the most likely mechanism of her hypercalcemia?

Accepted Answer

Lithium raises the calcium set-point for PTH suppression

Answer

Lithium elevates the calcium threshold for PTH suppression (shifts the set-point), resulting in inappropriately elevated PTH and mild hypercalcemia; this is usually reversible upon lithium discontinuation.

Question 3

A 26-year-old woman with type 1 diabetes presents with recurrent DKA episodes despite good outpatient compliance. She has celiac antibodies positive on screening. How does undiagnosed celiac disease contribute to DKA in type 1 diabetes?

Accepted Answer

Malabsorption leads to unpredictable glucose-insulin matching

Answer

Celiac disease-related malabsorption causes erratic carbohydrate absorption, making glucose-insulin matching unpredictable and precipitating hypoglycemia or hyperglycemia and DKA.

Question 4

A 65-year-old man with metastatic lung cancer develops calcium of 13.5 mg/dL, low PTH, low 1,25-dihydroxyvitamin D, and elevated PTHrP. Which mechanism best explains his hypercalcemia?

Accepted Answer

Humoral hypercalcemia of malignancy via PTHrP

Answer

Elevated PTHrP with suppressed PTH and low 1,25-(OH)2D is the hallmark of humoral hypercalcemia of malignancy, the most common cause of cancer-related hypercalcemia.

Question 5

A 40-year-old woman has an incidentally discovered 2.5 cm adrenal mass on CT for kidney stones. She has no hypertension or symptoms. Hormonal workup shows: normal aldosterone/renin ratio, normal 24-hour urine catecholamines, and 1 mg overnight dexamethasone suppression test shows cortisol of 3.8 mcg/dL. What is the next step?

Accepted Answer

Repeat imaging in 6–12 months and reassay hormones annually

Answer

An adrenal incidentaloma <4 cm that is hormonally inactive (cortisol suppresses to <5 mcg/dL on 1 mg DST) should be followed with repeat imaging at 6–12 months and annual hormonal reassessment per guidelines.

ITE - Internal Medicine In-Training Exam Practice Test

ITE - Internal Medicine In-Training Exam Practice Test

ITE Endocrinology and Metabolism 4