Acanthosis Nigricans

Acanthosis nigricans is skin thickening and pigmentation most typically developing in the axillae and nape of the neck (top); in dark-skinned people, the skin may have a leathery appearance (bottom). It is most often a skin manifestation of impaired glucose tolerance, but it may reflect internal malignancy, especially if onset is rapid and distribution is widespread.

Images provided by Thomas Habif, MD.