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Addisonian Hyperpigmentation — RACP Adult Medicine MCQ

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ModerateEndocrinologyAddisonian HyperpigmentationRACP Adult Medicine

A 35-year-old woman with Addison disease presents with generalised skin hyperpigmentation, particularly in skin creases (palmar creases), buccal mucosa, and scars. ACTH is markedly elevated. What is the mechanism of hyperpigmentation?

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Correct answer: A — Excess ACTH stimulating melanocortin-1 receptors

Generalised hyperpigmentation in Addison disease (especially in creases, scars, buccal mucosa, nipples) is caused by elevated ACTH (from loss of cortisol negative feedback). ACTH and its precursor POMC share a common precursor with MSH (melanocyte-stimulating hormone), which activates melanocortin-1 receptors (MC1R) on melanocytes. Secondary adrenal insufficiency does NOT cause hyperpigmentation (ACTH is low).

Reference: eTG Endocrine – 2024 – Adrenal Insufficiency; Endocrine Society 2016