Acanthosis nigricans.

Acanthosis nigricans (AN) is a dermopathy with a distinctive appearance that facilitates its diagnosis. Although an external condition, it is associated with a wide variety of less obvious internal conditions, either benign or malignant. Insulin resistance figures prominently in its benign associations and plays a primary role in its development. The development of AN in malignant conditions remains to be explained. AN rarely requires treatment, although the underlying condition usually does.