Typical and atypical dermoscopic presentations of dermatofibroma

Dermatofibroma is a common skin neoplasm that is usually easy to recognize, but in some cases its differentiation from melanoma and other tumours may be difficult.

To describe the dermoscopic features of dermatofibromas, with special emphasis on the characteristics of atypical patterns, and to calculate pattern frequency according to the patients age and gender, anatomical site and histopathological subtype.

Two groups of patients were consecutively seen, one with dermatofibromas that were surgically excised because of clinically and/or dermoscopically equivocal aspects or following patient request, and another with non-equivocal dermatofibromas. Each lesion was scored for previously reported global dermoscopic patterns and for additional features.

A typical pattern was observed in 92 of 130 (70.8%) lesions, whereas an atypical pattern, that we named the 'non Dermatofibroma (DF)-like' pattern, was seen in 38 of 130 (29.2%). Atypical dermatofibromas showed features reminiscent of different conditions, such as melanoma in 21(16.2%) cases, vascular tumour in six (4.6%), basal cell carcinoma in five (3.8%), collision tumour in three (2.3%) and psoriasis in three (2.3%). A significant association was found between the 'melanoma-like' pattern/'vascular tumour-like' pattern and males, whereas a trend was observed between the above-mentioned patterns and hemosiderotic/aneurysmal DFs. 'Peripheral pigment network and central white scar-like patch' pattern was found associated with females and classic histopathological variant of DF.

Dermatofibromas may display different morphological faces. The typical dermoscopic patterns allow a confident diagnosis, whereas a full surgical excision is always recommended in all doubtful cases.