ONYCHOMATRICOMA, A RARE NAIL TUMOR

Abstract Introduction/Objective Nail apparatus tumors are rare and can pose diagnostic challenges. Onychomatricoma (also called onychomatrixoma) is a rare tumor first described in 1992. It is a benign biphasic fibroepithelial tumor of the nail. It has been reported in Caucasians, often in females with a peak incidence in the fifth decade of life. Rare cases are also reported in children. The common location is in the fingernail (75%), presenting with yellowing of the nail plate (xanthonychia) and thick longitudinal band. Cutaneous horn, melanonychia, nail bleeding, and nail deformity with or without bony extension can also be seen. Histologic findings show increased nail thickness surrounded by a layer of Malpighian epithelium. The fibroepithelial tumor shows hyperplasia of two components including onychogenic epithelium and mesenchymal stroma. Methods/Case Report A 65-year-old Vietnamese female presented with longstanding dark yellowish ridging discoloration, thickening and nail plate deformity of the left fourth fingernail with appearance of onychomycosis. However, KOH mount and fungal cultures of the nail plate were negative for fungal microorganisms. There was no history of pain, trauma, or prior treatment. Microscopic analysis of transverse and longitudinal sections of the nail shows a biphasic neoplasm that penetrates the nail plate with multiple digitations. There was deep finger-like epithelial cell strands that form anastomosis as well as invaginations into the dermis. Characteristic filiform projections are lined by onychogenic epithelium composed mostly of basal and supra-basal cells that lack granular and corneum layers. The stroma was hypercellular and fibrillary with spindle-shaped fibroblastic cells, and a deep layer with dense collagen. Immunohistochemical stains of the lesion show diffuse expression for CD10 and CD34 in the stroma and negativity for Periodic Acid Schiff staining. Results (if a Case Study enter NA) N/A Conclusion While most of the literature on onychomatricoma has been reported in Caucasian population, little is known about this tumor in non-Caucasians. This case report of onychomatricoma in a Vietnamese woman contributes to the emerging literature of this rare nail apparatus tumor in non-Caucasian population. Clinical and histopathologic correlation is important to achieve prompt and correct diagnosis since delay would result in nail dystrophy and deformity.