What is a dermatofibroma

A dermatofibroma — also called a benign fibrous histiocytoma — is a firm, benign nodule that arises in the dermis. It is composed of a mixture of fibroblasts, histiocytes, and collagen, creating a dense, fibrous core. Clinically, dermatofibromas present as firm, slightly raised or dome-shaped papules, typically between 5 and 10 millimetres in diameter.

They are most common on the lower legs, particularly in women, though they can appear anywhere on the body. The overlying skin is often slightly pigmented — ranging from pink to brown — and the surface may appear slightly shiny or stretched.

Dermatofibromas sometimes follow minor skin trauma such as an insect bite, though many arise without any identifiable trigger. They are stable over time. Once formed, they rarely change significantly in size or appearance, and they do not transform into malignancy.

The clinical clue

If you pinch the skin on either side of a suspected dermatofibroma, the lesion characteristically dimples inward rather than protruding outward. This is because the fibrous core is tethered to the overlying epidermis. Most other papules and nodules will protrude when squeezed from the sides.

This dimple sign is useful but not always easy to elicit, and it is not specific enough to use in isolation. It works best as a clinical correlation — when you see the characteristic dermoscopic pattern and the lesion also dimples, your confidence is reinforced.

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