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Checkpoint inhibitor hypophysitis — SCE Endocrinology MCQ

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HardPituitaryCheckpoint inhibitor hypophysitisSCE Endocrinology

A 59-year-old man has fatigue 3 months after immune checkpoint inhibitor therapy for melanoma. Sodium is 129 mmol/L, 09:00 cortisol is 72 nmol/L, ACTH is low, TSH is low-normal and free T4 is 7 pmol/L. MRI shows mild pituitary enlargement. What is the most likely diagnosis?

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Correct answer: D — Immune checkpoint inhibitor-related hypophysitis

Immune checkpoint inhibitor-related hypophysitis is best because checkpoint inhibitor exposure with ACTH deficiency, central hypothyroidism and pituitary enlargement supports hypophysitis. The alternatives are less appropriate because primary adrenal failure raises ACTH; sick euthyroid syndrome does not cause hypocortisolism; phaeochromocytoma is catecholamine excess; Hashimoto's would raise TSH. The SCE teaching point is to integrate the clinical pattern, biochemistry and context rather than treating an isolated result.

Reference: Society for Endocrinology immune checkpoint inhibitor endocrine guidance