Dermatofibroma (fibroma durum, fibrous histiocytoma, histiocytomas, nodular subepidermal fibrosis, sclerosing hemangioma) is a very common benign skin lesion occurring anywhere on the body surface with predilection for the extremities, especially the lower legs. The cause of a dermatofibroma is unknown, but responses to injuries, both external, e.g., insect bites, and internal, e.g., ruptured follicles, have been considered.
Clinically, dermatofibromas appear as firm, single or multiple papules, plaques or nodules usually characterized by a color variable from light-brown to dark-brown, purple, red or yellow. Dermatofibromas range from 0.5 mm to 1 cm in diameter. They are usually indolent, sometimes pruritic and may ulcerate. Characteristically, dermatofibromas are hard and freely movable over deeper tissue and lateral compression can produce a dimple-like depression in the overlying skin. An important clinical differential diagnosis is with dermatofibrosarcoma protuberans, especially in unusually large dermatofibromas. Other differential diagnoses include blue nevi and, first of all, melanomas.
Dermatofibroma is probably the only entity within the spectrum of pigmented skin lesions where palpation is of diagnostic relevance. This fact should be kept in mind when judging only the dermoscopic image of a given dermatofibroma. Nevertheless, the dermoscopic features of dermatofibroma are fairly characteristic and in most instances allow a definitive diagnosis with a high degree of certainty. The global pattern of dermatofibroma is considered unspecific or, rarely, multicomponent, although a reticular pattern in an annular distribution can be easily observed in many cases. In this context it should be mentioned that dermatofibromas and solar lentigines are the only non-melanocytic pigmented skin lesions revealing a pigment network.