Acanthosis nigricans

Brown-to-black, poorly defined, velvety, papillomatous, hyperkeratotic, hyperpigmentation of the skin, usually found in body folds, such as the posterior and lateral folds of the neck, the armpits, groin, navel, and forehead. It is most common in obese people overproducing insulin. It is associated with endocrine dysfunction especially insulin resistance and hyperinsulinaemia, as seen in diabetes mellitus (type 2), that activates the insulin-like growth factor receptors, leading to proliferation of keratinocytes, fibroblasts and other cells in the skin, as well as other growth factor receptors. Cf. acantholysis

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