Melanocytic matricoma: case confirmation of a recently described entity.

BACKGROUND: In 1999, Carlson et al. reported two cases of a matrical neoplasm that recapitulates the bulb of the anagen hair follicle, which they designated as melanocytic matricoma. METHODS: Here we report a similar case in a 78-year-old white male, who presented with a 0.4 cm purple-black firm papule in the left preauricular area. RESULTS: Histologically, the tumor is composed of a dual cell population including admixed epithelial matrical and supramatrical cells with "shadow" cell formation and pigmented dendritic melanocytes. Immunohistochemical studies for cytokeratin highlighted the epithelial component and studies for S-100 protein, HMB-45, and vimentin confirmed the melanocytic component. The differential diagnosis considered includes pigmented variants of pilomatricoma, matrical carcinoma, basal cell carcinoma and malignant melanoma. CONCLUSIONS: The case reported herein is the first confirmation of melanocytic matricoma, a distinctive adnexal neoplasm with characteristic clinical and pathologic features, which differentiate it from pigmented pilomatricoma.