Which of the following is a hallmark sign of Addison's disease?

• A. Hyperpigmentation of the skin
• B. Moon face
• C. Buffalo hump
• D. Truncal obesity

Answer: (A)

Hyperpigmentation of the skin is a hallmark of Addison's disease because the adrenal problem is primary, causing the pituitary to release more ACTH to try to stimulate cortisol production. ACTH is produced from the same precursor as melanocyte-stimulating hormone, so the excess ACTH also drives increased melanin production. That extra melanin leads to darker skin and mucous membranes, especially in areas of friction or sun exposure, and it can appear in scars or creases as well. This pigment change is a classic clue to primary adrenal insufficiency.

The other signs—moon face, buffalo hump, and truncal obesity—are features of Cushing's syndrome, which results from excess cortisol rather than cortisol deficiency. They reflect fat redistribution and characteristic facial and trunk changes seen with high cortisol levels, not Addison's.