Giant onychomatricoma: report of two cases with rare clinical presentation.

BACKGROUND: Onychomatricoma was reported for the first time by Baran and Kint as a rare nail matrix tumor with specific clinical and histologic features, including a macroscopic appearance of filiform digitations originating from the nail matrix which are inserted in the nail plate.(1) The appearance of the lesion may resemble that of an "anemone." All previous reports have been mostly from Europe, with only one case from North America. These are the first case reports from Mexico. They show rare clinical characteristics, in particular tumor involving the entire nail matrix.

METHODS: Two cases are presented: Case 1, a 59-year-old man with a 2-year history of deformity of the entire nail apparatus of the right thumb, clinically suggestive of onychomatricoma; Case 2, a 45-year-old woman with a 3-year history of gradual nail dystrophy, initially misdiagnosed as onychomycosis and treated unsuccessfully for several months with antimycotics by a general physician. In both cases, the entire nail plate was affected and, because of the clinical appearance, nail exploration and excisional biopsy of the tumors at the nail matrix were performed.

RESULTS: During nail matrix surgical exploration, including avulsion of the nail plate, characteristic digitiform projections that were firmly attached to the nail plate were observed. In both cases, the entire nail matrix was affected, producing a giant form of onychomatricoma. Hematoxylin and eosin stain showed characteristic filiform projections that corresponded to the clinical appearance, with elongated epithelium from the nail matrix and fibromyxoid stroma with multiple basophilic cells, and typical clefts in between.

CONCLUSIONS: Onychomatricoma has a classical clinical appearance; however, it is difficult to identify, as it is not until surgery, when the typical filiform projections are more visible, that the diagnosis can be made. Onychomatricoma is a rare tumor. The involvement of the entire nail matrix, with secondary nail dystrophy, in both cases presented here makes them interesting case reports of this unusual form of tumor.