Track

Case Reports

Abstract

Pigmented onychomatricoma is a rare fibroepithelial tumor that arises from the nail matrix and onychodermis. We present a case of a 57-year-old female with a pigmented nodule on the distal left small toe. An excisional biopsy of the lesion was performed and demonstrated a spindle cell tumor within both the epidermis and dermis with papillomatous projections of epithelium intercalating into the nail plate. There was a focal proliferative component with small buds of epithelium emanating from the epidermis that demonstrated onycholemmal differentiation, with differentiation into onychocytes. The dermis contained a cellular component with areas of compact collections of spindle cells strongly highlighted by CD34. S-100, HMB45, MART-1, and p16 immunohistochemical stains revealed scattered melanocytes within the matrix epithelium but were negative in the spindle cells. A Fontana-Masson special stain highlighted pigment within the epithelium. The Ki-67 proliferation index in the spindle cells was <1%. Melanonychia is a commonly encountered entity and despite the few reported cases of pigmented onychomatricoma, the histological overlap with other conditions makes it an important differential to consider. The most common presenting feature is longitudinal pachymelanonychia, making this entity important to differentiate from ungual melanoma, pigmented ungual Bowen’s Disease, pigmented onychopapilloma and fungal melanonychia. A cellular variant of a pigmented onychomatricoma is even less frequent and to our knowledge, has not been reported in the literature