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Secondary adrenal insufficiency — SCE Endocrinology MCQ

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HardAdrenalSecondary adrenal insufficiencySCE Endocrinology

A woman with an adrenal incidentaloma takes carbamazepine. Her cortisol after 1 mg overnight dexamethasone is 96 nmol/L, but serum dexamethasone is subtherapeutic. She has no Cushing stigmata. What is the most defensible interpretation?

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Correct answer: B — Repeat testing because accelerated dexamethasone metabolism can cause false nonsuppression

Explanation lettering: B = shown as A · D = shown as B · A = shown as D

D is correct. CYP3A4 induction by carbamazepine can reduce dexamethasone exposure and create a false-positive overnight suppression test; the measured subtherapeutic dexamethasone demonstrates that the test condition failed. Repeat or alternative validated assessment is required. The 50 nmol/L threshold assumes adequate dexamethasone exposure. A single compromised test proves neither mild nor overt Cushing syndrome, carbamazepine does not simply suppress cortisol production, and surgery requires confirmed hormonal assessment plus individualized risk–benefit evaluation.

Reference: 2023 ESE adrenal incidentaloma guideline: https://academic.oup.com/ejendo/article/189/1/G1/7198474