A 28-year-old woman develops central obesity, hypertension, glucose intolerance, purple striae, and proximal muscle weakness. Morning serum cortisol is elevated and does not suppress with low-dose dexamethasone but suppresses with high-dose dexamethasone. The most likely pathology driving her symptoms is:

• A Adrenal cortical adenoma secreting cortisol
• B ACTH-secreting pituitary adenoma (Cushing disease) ✓
• C Ectopic ACTH secretion by small cell lung carcinoma
• D Primary adrenal cortical hyperplasia

Explanation

Suppression with high-dose dexamethasone (but not low-dose) is the hallmark distinguishing pituitary ACTH-secreting adenoma (Cushing disease) from other causes. Adrenal adenomas and ectopic ACTH sources typically fail to suppress even with high-dose dexamethasone. Pituitary corticotroph adenomas retain partial glucocorticoid feedback sensitivity at supraphysiologic doses. Cushing disease represents the most common cause of endogenous hypercortisolism.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.