Acanthosis nigricans presents as asymptomatic tan to dark brown velvety plaques usually on the posterior neck and intertriginous areas. It is often a cutaneous manifestation of insulin resistance. Histopathologically, lesions demonstrate hyperkeratosis, papillomatosis, acanthosis, and a thickened dermis. Acanthosis nigricans at the site of repeated insulin injections has been reported at least twice previously in the literature.1,2 The activation of insulinlike growth factor (IGF) receptors due to high circulating levels of insulin likely causes this lesion.3
Mailler-Savage EA, Adams BB. Exogenous Insulin-Derived Acanthosis Nigricans. Arch Dermatol. 2008;144(1):126–127. doi:10.1001/archdermatol.2007.27
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