Acanthosis nigricans usually appears slowly and doesn't cause any symptoms other than skin changes.
Eventually, dark, velvety skin with very visible markings and creases appears in the armpits, groin, and neck. Sometimes, the lips, palms, soles of feet, or other areas may be affected.
Your physician can usually diagnose acanthosis nigricans by simply looking at your skin. A skin biopsy may be needed in unusual cases.
If no clear cause of acanthosis nigricans is obvious, it may be necessary to search for one. Your physician may order blood tests, an endoscopy, or x-rays to eliminate the possibility of diabetes or cancer as the cause.
Morelli JG. Diseases of the Epidermis. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap. 656.