The Diagnosis: Dermatofibroma
On dermoscopy, a central stellate, white, scarlike patch was seen (Figure). On both legs the patient had several additional brown 5- to 7-mm papules with similar dermoscopic features.
Dermatofibromas are common benign fibrosing tumors that appear as firm papules or plaques with variable color, commonly on the legs. Typically, lateral compression of a dermatofibroma causes downward displacement, called a positive dimple sign. On histology, fibroblasts and myofibroblasts can be seen as short intersecting fascicles with variable inflammatory cells and induction of adjacent structure hyperplasia. The etiology of dermatofibromas is unclear, though some are thought to be secondary to trauma or arthropod bites.1 Because these tumors are benign, the correct diagnosis can avoid unnecessary biopsies or other procedures.
The dermoscopic features of dermatofibromas have been well established.2 As perhaps the most easily identified structure, scarlike patches were seen in as many as 92% (22/24) of dermatofibromas in one study by Ferarri et al,3 while pigment networks also are commonly seen.2 In our case, given the surrounding dense tattoo deposition, it was difficult to ascertain any pigment network. However, the scarlike central patch was clearly apparent by dermoscopy.
Because dermatofibromas are hypothesized to be secondary to trauma, presumably applying tattoos also may cause dermatofibromas. Limited cases have described dermatofibromas arising in tattoos applied several months to years prior.4-6 No prior cases utilized dermoscopy. In our case, clinical examination and dermoscopy clearly demonstrated features consistent with a dermatofibroma, and the patient had more characteristic dermatofibromas scattered elsewhere on both legs. The patient was reassured that the lesions were benign and that the depigmentation was likely secondary to the process of dermatofibroma growth. She declined any treatment.