Bowen's disease clinically simulating an onychomatricoma.

Onychomatricoma (OM) is an uncommon benign tumor clinically characterized by a thickened yellowish nail with transverse over curvature. A pigmented variant has recently been described. Histologically, the diagnosis requires 3 prerequisites: (1) a fibroepithelial tumor consisting of 2 portions: the proximal zone (under the proximal nailfold, characterized by deep epithelial invaginations and a fibrillary and fibrocytic stroma), whereas the distal zone (corresponding to the lunula) presents with multiple digitations along its connective tissue axes; (2) a matricial tumor typified by a thick keratogenous zone; and (3) a thick nail plate, perforated by cavities. We describe a case that appears clinically identical to a pigmented OM, but with histologic malignant patterns. Because histologic features were consistent with Bowen's disease, we ruled out a malignant OM. We report a new variant of Bowen's disease presenting as OM, and this observation underlines the necessity for a histologic assessment of all forms of OM, especially those associated with a pigmented band (a sign sometimes observed in Bowen's disease).