Acanthosis Nigricans(AN) It is a common condition characterized by velvety, hyperpigmented plaques on the skin. Intertriginous sites, such as the neck and axillae, are common sites for involvement. Less frequently, acanthosis nigricans appears in other skin sites or on mucosal surfaces.
Clinical recognition of AN is important because the disorder can occur in association with a variety of systemic abnormalities, many of which are characterized by insulin resistance. Obesity and diabetes mellitus are among the most frequently associated disorders. Rarely, acanthosis nigricans develops as a sign of internal malignancy.
PATHOPHYSIOLOGY of AN
When the serum insulin level is within normal limits, it crosses the dermoepidermal junction, binds to the classical insulin receptors, and brings about a change in carbohydrate, lipid, and protein metabolism, but it does not increase the proliferation of keratinocytes. However, at higher concentrations, it can bind to the insulin-like growth factor 1 receptors (IGF-1Rs) stimulate proliferation of keratinocytes and fibroblasts, leading to AN. Also, IGF-binding proteins (IGFBPs) bind to IGF-1 and thereby regulate the levels of metabolically active “free” IGF-1. These IGFBP-1 and IGFBP-2 are decreased in obese patients with hyperinsulinemia, which increases the plasma concentrations of free IGF-1, promoting cell growth, and differentiation of keratinocytes leading to AN.
Pictures courtesy from Book- StatPearls, Treasure Island (FL): Stat Pearls Publishing; 2019 Jan-.Acanthosis Nigricans, Mark F. Brady; Prashanth Rawla.