The Relation of Onychomatricoma to Onychodermis in the Nail Unit

Abstract

Dear Editor: Onychomatricoma is a very rare tumor of the nail unit. It is originally reported to be a benign tumor of the nail matrix as the name implies1. However, histopathologically, it is a fibroepithelial tumor with well-established features. Recently, based on its histopathological and immunohistochemical features, the concept of epithelial onychogenic tumor with onychogenic mesenchyme is being suggested for this peculiar mixed tumor2. Nevertheless, the authors mention that the term onychomatricoma is short and sanctioned by usage, and justifies such statement. We recently demonstrated the presence of specialized mesenchyme containing onychofibroblasts beneath the nail matrix and nail bed3,4. Based on this finding, we proposed new terminology onychodermis for specialized mesenchyme because it is histologically and immunohistochemically distinct from the dermis of other parts of the nail unit. This study evaluates the relation of onychomatricoma to onychodermis in the nail unit we performed CD10 immunohistochemistry in one case of onychomatricoma sample (a kind gift from Dr Robert Baran and Dr Josette Andre). Immunohistochemical staining was performed using the monoclonal antibody of CD10 (1 : 50, clone 56C6; Novocastra, Newcastle, UK). Normal nail unit is being used as a control. As reported previously, CD10 is strongly expressed in the onychodermis below the nail matrix and nail bed within normal nail unit (data not shown). In the onychomatricoma case, CD10 is being expressed diffusely in the stoma (Fig. 1). Fig. 1 Immunohistochemical staining of CD10 in onychomatricoma. CD10 was diffusely expressed in the stroma of onychomatricoma. (A) Low-power view (×40), (B) highpower view (×200). Onychomatricoma is a subungual tumor which consists of epithelial onychogenic tumor with onychogenic mesenchyme. Based on its components and location, the onychodermis, which is located below the nail matrix and nail bed, might be related to the occurrence of the onychomatricoma. In addition, in our case, the CD10, which is a marker of the onychodermis, is expressed in the stroma of the onychomatricoma, supporting that onychomatricoma might derive from the onychodermis. According to a previous study using organotypic cultures, the fibroblasts around the nail matrix induced hard keratin expressions in the non-nail-matrix keratinocytes through epithelial-mesenchymal interactions5. Thus, the onychodermis containing onychofibroblasts may play an important role in nail formation through epithelial-mesenchymal interactions. Epithelial lesion in onychomatricoma might be induced by mesenchymal tumor occurring in the onychodermis. To deduce, the onychodermis might be involved in the histogenesis of the onychomatricoma. In conclusion, onychomatricoma seems to be closely related to the onychodermis. It might be a derivative from onychoderms.