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Ectopic ACTH syndrome — SCE Endocrinology MCQ

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HardAdrenalEctopic ACTH syndromeSCE Endocrinology

A 51-year-old man with severe Cushingoid features has ACTH-dependent hypercortisolism. Pituitary MRI shows a 3 mm lesion, but inferior petrosal sinus sampling has no central-to-peripheral ACTH gradient after CRH. What is the most likely source?

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Correct answer: A — Ectopic ACTH secretion

Lack of a central ACTH gradient on IPSS supports ectopic ACTH secretion despite a small pituitary incidentaloma. Cushing's disease usually shows central ACTH enrichment. Small pituitary lesions are common incidental findings and should not override dynamic localisation.

Reference: Endocrine Society Cushing's Syndrome Guideline