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Cushing disease — RCPSC IM MCQ

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HardEndocrinologyCushing diseaseRCPSC IM

A patient has confirmed ACTH-dependent hypercortisolism and a 5-mm pituitary lesion, but noninvasive testing is discordant and an ectopic source remains possible. What is the best next test before pituitary surgery?

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Correct answer: C — Perform inferior petrosal sinus sampling

The best answer is “Perform inferior petrosal sinus sampling”. Small incidental pituitary lesions are common. When ACTH-dependent Cushing syndrome is established but source localization is discordant, inferior petrosal sinus sampling can distinguish pituitary from ectopic ACTH before irreversible surgery. Sampling is interpreted using central-to-peripheral ACTH gradients after stimulation and should be performed where technical and endocrine expertise are available.

Reference: Endocrine Society clinical practice guideline library: https://www.endocrine.org/clinical-practice-guidelines