Mimickers and differential diagnosis

Dermatofibroma has a relatively narrow differential, but the mimickers that exist are clinically important.

Desmoplastic melanoma

This is the rare but critical mimicker. Desmoplastic melanoma is a variant of melanoma that contains dense fibrous tissue, and can present as a firm, pale nodule — sometimes with features that overlap with the central white patch of a dermatofibroma.

Desmoplastic melanoma is uncommon, but it is important because it can be missed precisely because it looks bland. Features that should raise suspicion include a lesion that is larger than a typical dermatofibroma (over 10mm), atypical vascular patterns within the white area, a history of growth or change, or location on sun-damaged skin of the head and neck rather than the typical lower legs.

Melanocytic naevus

A dermal naevus on the lower leg can occasionally mimic dermatofibroma. Dermal naevi tend to be softer, lack the dimple sign, and under dermoscopy show a cobblestone pattern or structureless brown areas rather than the central white patch with peripheral network.

Dermatofibrosarcoma protuberans

Dermatofibrosarcoma protuberans (DFSP) is a rare, low-grade soft tissue tumour that can clinically resemble a dermatofibroma — both are firm dermal nodules. DFSP tends to be larger, grows more slowly but progressively, and may have a more indurated or plaque-like quality. Dermoscopically, DFSP lacks the classic central white patch and peripheral network of dermatofibroma.