Abstract

71-year-old African American female presents with diffuse toenail hyperpigmentation, since childhood. She reports the toe becoming swollen and painful, 4 months prior to seeking medical attention. There is no history of toenail trauma, bleeding or discharge. Physical examination shows positive Hutchinson sign of the right fifth toenail with pigmentation extending down into proximal nailfold. Soft tissue swelling with no evidence of bone involvement is seen on X-ray. Dermatoscopy reveals notably thickened nail plate with longitudinal ridging and honeycomb-like appearance. Nail unit excisional biopsy shows nail matrix epithelial hyperplasia forming “glove finger” papillary projections, and marked verrucous epithelial hyperplasia of the nail bed epithelium with hyperkeratosis. The moderately cellular stroma exhibits fibroblastic proliferation with slight increase in vascularity, few mast cells and scattered melanin pigment. Vertically oriented deep stromal invaginations surrounding optically empty spaces in a characteristic V-shaped configuration are seen in the proximal portion of the tumor. CD34 stains the stromal fibroblastic cells which are negative for SOX-10, S-100 and Melan-A. The findings are consistent with diagnosis of Onychomatricoma. This is a benign tumor of nail matrix epithelium classically presenting with xanthonychia, ungual hyperkeratosis, and nail plate splinter hemorrhages with its longitudinal over-curvature. It is important for clinicians and pathologists to be aware of its rare pigmented variant which is a clinical simulator of nail unit melanoma, more often presenting with longitudinal melanonychia rather than diffuse or total melanonychia. To our knowledge this is the only reported case of pigmented onychomatricoma originating in childhood in an African American female.

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