Hypopigmented onychocytic matricoma as a clinical mimic of onychomatricoma: clinical, intraoperative and histopathologic correlations.

Onychocytic matricoma is a newly described matrical tumor of the nail unit that clinically presents with localized thickening of the nail plate and melanonychia and represents a benign acanthoma of onychocytes. Onychocytic matricoma can be classified according to its histopathologic type (acanthotic, papillomatous or keratogenous with retarded maturation) and pigmentation (pigmented, melanocytic or non-pigmented). However, there are no published reports of non-pigmented onychocytic matricoma. We report a case of hypopigmented onychocytic matricoma that presented with a thickened nail plate, xanthonychia and histopathologic features of acanthosis, prekeratogenous zone and keratogenous zone cells forming pseudosquamous eddies, and minimal pigmentation with Fontana staining. We also provide detailed clinical, intraoperative and histopathologic correlations of this rare tumor. Both clinicians and dermatopathologists should be aware that onychocytic matricoma can present with xanthonychia, thickening of the nail plate and mimic an onychomatricoma.