Acanthosis nigricans is a medical sign characterised by brown-to-black, poorly defined, velvety hyperpigmentation of the skin. It is usually found in body folds, such as the posterior and lateral folds of the neck, the armpits, groin, navel, forehead and other areas. It is associated with endocrine dysfunction, especially insulin resistance and hyperinsulinaemia, as seen in diabetes mellitus...