Photo Rounds

Discoloration under arm

A mother brought her overweight 10-year-old daughter to the family physician (FP) because she was concerned about a “dirty area” under the child's arms and on her neck that couldn’t be cleaned. There was a strong family history of diabetes, but the girl’s blood sugar levels were normal.

What's your diagnosis?


The FP diagnosed acanthosis nigricans (AN) in this patient and continued to work with the girl and her family on the issues of diet, exercise, and weight loss. AN is a skin condition usually associated with insulin resistance (IR) and is seen in patients with type 2 diabetes, obesity, and polycystic ovary syndrome. AN is sometimes associated with malignancy, primarily adenocarcinoma of the stomach, colon, ovary, pancreas, rectum, and uterus.

AN results from long-term exposure of keratinocytes to insulin. Keratinocytes have insulin and insulin-like growth receptors on their surfaces, and the pathogenesis of this condition may be linked to insulin binding to insulin-like growth receptors in the epidermis.

AN ranges in appearance from diffuse streaky thickened brown velvety lesions to leathery verrucous papillomatous lesions. It is commonly located on the neck or skin folds (eg, axillae, inframammary folds, groin, and perineum). Weight loss through diet and exercise helps reverse the process, probably by reducing both IR and compensatory hyperinsulinemia. The use of keratolytic agents (eg, salicylic acid) may improve the appearance of the lesions. Other drugs such as metformin, topical retinoids, and topical vitamin D analogs have also been used to treat AN.

Photos and text for Photo Rounds Friday courtesy of Richard P. Usatine, MD. This case was adapted from: Smith M. Acanthosis nigricans. In: Usatine R, Smith M, Mayeaux EJ, et al, eds. The Color Atlas of Family Medicine. New York, NY: McGraw-Hill; 2009:942-944.

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