Plaque-like dermatofibroma: A distinct and rare benign neoplasm?

Unusual large dermatofibromata are reported in a 40-year-old man and a 48-year-old man, who both presented with plaques on a lower limb. The largest plaque in each case was well-defined, reddish brown, indurated and measured 50 mm x 30 mm and 70 mm x 40 mm, respectively. Several satellite lesions were present around the large plaques. Dermoscopic examination showed diffuse homogenous pigmentation in the absence of other diagnostic criteria for dermatofibroma. Light microscopy of biopsies from each patient displayed similar features. There was a dermal proliferation of fibrohistiocytic cells that entrapped intervening thickened collagen fibres. The overlying epidermis was acanthotic, and in some instances this showed basal hyperpigmentation. There was no evidence of malignancy. Immunohistochemical staining was positive for Factor XIIIa and negative for CD34. Based on the histological findings, a diagnosis of dermatofibroma was made for each of these cases. Fewer than 20 adult cases of large dermatofibroma of this scale, designated giant dermatofibroma, have been reported to date; and only two have shown a plaque-like appearance, the remainder being pedunculated. The authors propose plaque-like dermatofibroma as a variety of large dermatofibroma distinct to pedunculated giant dermatofibroma.