Pigmented Onychomatricoma Presenting as Pachymelanonychia Striata: A Case Report and Review of Literature.

Introduction: Onychomatricoma is a fibroepithelial tumor derived from the nail matrix and onychodermis. Many clinical and histological variants have been described. Pigmented onychomatricoma is a rare variant which presents as longitudinal pachymelanonychia.

Case presentation: We report the details of a 41-year-old female who presented with blackening and thickening involving more than half of the left middle fingernail for the past 10 years. Dorsal plate onychoscopy revealed longitudinal parallel white, gray, and black bands, while onychoscopy of the distal free edge demonstrated a thickened nail plate with "wood worm" cavities. The histopathological examination of the excised tumor revealed a pigmented onychomatricoma.

Conclusions: Onychomatricoma is one of the nail tumors presenting as pachyonychia striata apart from onychocytic matricoma and onychocytic carcinoma. A pigmented onychomatricoma may closely mimic fungal melanonychia, pigmented onychopapilloma, pigmented ungual Bowen's disease, and ungual melanoma. Noninvasive techniques like onychoscopy and imaging studies like ultrasonography and magnetic resonance imaging are helpful in differentiating it from pigmented ungual Bowen's disease and ungual melanoma, even though diagnostic confirmation requires an excisional biopsy.