Terra Firma-Forme Dermatosis Misdiagnosed as Nevoid Acanthosis Nigricans

Terra firma-forme dermatosis (TFFD) is a clinical condition characterized by brown-gray, velvety, pigmented patches or plaques, resembling dirt on the skin. Nevoid acanthosis nigricans (NAN) is a rare and recently described form of acanthosis nigricans occurring during childhood or early adulthood. Herein we describe a patient with TFFD, initially misdiagnosed as NAN. The patient had developed hyperkeratotic and hyperpigmented plaques on and around the umbilicus during pregnancy. Though regular in bathing practices, she could not clear away the lesions and concerned marks for inesthetic appearance. Histopathological findings were compatible with NAN, and she was prescribed 10% urea lotion. On a dramatic healing after 3 weeks, a diagnosis of TFFD is considered and confirmed by the lesions getting wiped away by vigorous rubbing with alcohol pads. We discuss the key points of differentiating TFFD from NAN, and underline the importance of alcohol test for accurate diagnosis.