A frustrated mother brings in her 14-year-old daughter for evaluation of darkening skin. When the girl was 10, the skin around her neck became darker than it had been; the problem quickly spread to involve skin folds under her arms, in the groin, on the dorsa of her toes, and on her knuckles. Blaming the problem on a lack of washing, the mother has instructed the girl to scrub vigorously— but while this process removes a bit of the dark skin, by the next day, the affected areas are dark again.

The patient is 5 ft 2 in and weighs 175 lb; she is clearly overweight. According to her mother, the girl’s recent blood work indicated a fasting blood glucose level of 120 mg/dL, a cholesterol level of 280 mg/dL, and a triglyceride level > 300 mg/dL. Both agree that the girl’s diet—mostly snacks and fast food, nothing green or fresh—leaves a lot to be desired. Family history is positive for diabetes and heart disease. The patient had her first menstrual period a year ago.

On examination, all intertriginous areas (skin folds) are quite dark and velvety to rough, with many tiny skin tags confined to the darkened areas. In addition, the dorsal aspects of her knuckles are similarly affected. Attempts at removing or reducing the dark areas with alcohol pads fail. The rest of the patient’s skin is free of notable changes (eg, excessive dryness, hirsutism, or acne).