Pituitary Disorders USMLE Step 1 Practice Question
A 41-year-old man with recently diagnosed Cushing syndrome secondary to a pituitary corticotroph adenoma presents with hypertension (160/98 mmHg), tachycardia (102 bpm), and hypokalemia (K+ 2.9 mEq/L). Laboratory studies reveal hyperglycemia (285 mg/dL) and elevated 24-hour urinary free cortisol (450 mcg/24h). MRI confirms a 1.2-cm sellar mass. He denies polyuria. Which pathophysiologic mechanism best explains these metabolic derangements?
Answer choices
- AExcess cortisol causes hypokalemia via renal potassium wasting and hyperglycemia via increased hepatic gluconeogenesisCorrect answer
- BAldosterone deficiency leads to sodium retention and potassium depletion
- CImpaired potassium absorption in the GI tract is the primary mechanism of hypokalemia
- DACTH excess directly stimulates pancreatic beta cells to produce insulin-resistant diabetes
- EConcurrent catecholamine excess from adrenal medulla causes hypokalemia and hyperglycemia
- FExcessive ADH secretion from the corticotroph adenoma causes hypokalemia via dilutional mechanisms and hyperglycemia via osmotic diuresis
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