Desmoplastic spitz nevus: report of a case and review of the literature.

Desmoplastic spitz nevus (DSN) is an uncommon melanocytic lesion. The histologic features of this benign tumour may mimic those of certain benign (dermatofibroma and desmoplastic cellular blue nevus) or malignant (metastatic carcinoma and malignant melanoma) neoplasms. We report the case of a male with a DSN, and also review the clinical characteristics, histologic features and differential diagnosis of this extremely rare lesion. The lesion is identified as an asymptomatic reddish-brown dome-shaped papule on the forearm. Microscopic examination showed a symmetric lesion in the dermis. The neoplastic cells were large and epithelioid-shaped, and were either isolated as individual cells or arranged in small nests in a paucicellular hyalinized stroma. Nuclei were large and vesicular with small nucleoli and no mitoses. Diffuse expression of S100 and the absence of staining with antibodies to melan-A and HMB45 was observed. A diagnosis of DSN with free margins was made. The histologic presentation of this benign lesion mimics both benign and malignant neoplasms. The immunohistochemical profile (S100 positive, HMB-45 negative and cytokeratin negative) may be helpful to differentiate it from other lesions.