A patient suspected of Cushing syndrome undergoes dexamethasone testing. Low-dose dexamethasone fails to suppress cortisol. High-dose dexamethasone suppresses cortisol by 60%. This pattern is most consistent with:

• A Adrenal cortical adenoma
• B Ectopic ACTH secretion from small cell lung cancer
• C Exogenous glucocorticoid use
• D Pituitary ACTH-secreting adenoma ✓

Explanation

In Cushing disease from a pituitary adenoma, high-dose dexamethasone suppresses cortisol because the tumor retains partial feedback sensitivity. Ectopic ACTH secretion and adrenal adenomas do not suppress with high-dose dexamethasone. Exogenous glucocorticoid use would suppress ACTH and endogenous cortisol, but this patient has elevated cortisol, ruling out that option.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.