Sclerosing nevus with pseudomelanomatous features

BACKGROUND: Among the pigmented lesions with a central area of scar, we found a group of cases histologically characterized by striking architectural alteration of the melanocytic component, but with no cytological atypia and mitotically quiescent. The aim of the current study was to assess the biological nature of such lesions. METHODS: We selected 19 of these melanocytic neoplasms that had the following characteristics: (a) a clinically evident whitish central area suggestive of regression (with no history of a previous surgical procedure or trauma), (b) histological features of fibrous scar-like tissue at the center of the lesion, (c) the presence of large, confluent and unusually shaped melanocytic nests at the dermoepidermal junction and in the dermis, (d) a pagetoid spread of melanocytes above the epidermal basal layer and (e) remnants of nevus tissue at the border of the scar. The lesions showed no evidence of cytological atypia, expansive nodules of melanocytes, significant numbers of mitoses or cellular necrosis. RESULTS: All the cases have been followed up and none have recurred or metastasized. Histologically, these neoplasms have important similarities with the so-called recurrent nevus, nevi on lichen sclerosus and nevi developed during or following cutaneous inflammatory and sclerosing processes. The origin of the scar in each case was obscure but was probably related to minor unnoticed trauma or to chronic friction on a nevus. In few cases, the fibrosis was probably the result of partial regression of the nevus or a sequel to folliculitis. The pseudomelanomatous features appear to be related to the presence of the scar, as already reported for nevi that are involved in fibrotic or scarring processes. In our study, the nevi involved in the fibrotic process were congenital nevi and common or dysplastic nevi. One case was a Spitz nevus. CONCLUSIONS: From our data we concluded that, despite their worrisome clinical and histological aspect, the lesions described in this case series were most probably benign melanocytic nevi, involved by a fibrotic process combined with pseudomelanomatous proliferation. The lack of cytological atypia, mitoses and expansive nodules allowed us to differentiate these lesions from regressing melanomas.