A 38-year-old woman presents with weight gain, proximal muscle weakness, easy bruising, and a 2 cm right adrenal mass on CT (HU +18 on non-contrast). Serum ACTH is undetectable. Overnight 1 mg dexamethasone suppression test shows cortisol of 9.5 µg/dL. Which is the next best investigation?
- A Adrenal vein sampling is not indicated; proceed to right adrenalectomy ✓
- B High-dose dexamethasone suppression test
- C CRH stimulation test
- D Bilateral inferior petrosal sinus sampling
Correct answer: A. Adrenal vein sampling is not indicated; proceed to right adrenalectomy
Explanation
Undetectable ACTH with failed low-dose dexamethasone suppression and a unilateral adrenal adenoma (density +18 HU is within adenoma range) localises the source to the adrenal gland — ACTH-independent Cushing's syndrome. High-dose dexamethasone, CRH test, and IPSS are used for ACTH-dependent disease. Adrenal vein sampling is used to lateralise primary aldosteronism. The appropriate next step is right adrenalectomy.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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