Hyperpigmentation in Addison's disease is primarily due to which mechanism?

• A. Elevated cortisol causing pigment production
• B. Decreased cortisol leading to increased ACTH and MSH
• C. Increased aldosterone causing pigment production
• D. Decreased MSH production

Answer: (B)

Hyperpigmentation in Addison's disease comes from increased stimulation of melanocytes due to high ACTH levels. When the adrenal glands can’t produce cortisol, negative feedback to the pituitary is reduced, so ACTH secretion rises. ACTH is produced from the same precursor as melanocyte-stimulating hormone, so the surge in ACTH also means more MSH activity. The excess MSH boosts melanin production in the skin and mucous membranes, leading to the characteristic darkening. The other options don’t fit: cortisol would be low, not elevated; aldosterone isn’t linked to pigment changes; and decreased MSH would reduce pigment instead of increasing it.