skip to main content

Cushing Syndrome (ACTH-dependent) — RACP Adult Medicine MCQ

Instant feedback + full explanation. One question, done properly.

ModerateEndocrinologyCushing Syndrome (ACTH-dependent)RACP Adult Medicine

A 45-year-old woman presents with weight gain (central obesity with thin limbs), moon face, dorsal fat pad, purple striae, easy bruising, and proximal myopathy. She has new-onset diabetes and hypertension. 24-hour urine free cortisol is 4× ULN. Overnight dexamethasone suppression test shows non-suppressed cortisol (350 nmol/L). ACTH is elevated. What is the most likely diagnosis?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: E — Cushing syndrome

Clinical features of cortisol excess with elevated 24-hour urine free cortisol, non-suppressed cortisol on 1 mg overnight DST, and elevated ACTH indicates ACTH-dependent Cushing syndrome. The next step is high-dose dexamethasone suppression test and pituitary MRI to differentiate pituitary adenoma (Cushing disease, ~70%) from ectopic ACTH (~15%). Inferior petrosal sinus sampling may be needed.

Reference: Endocrine Society – 2015 – Cushing Syndrome; ESA 2024