Histopathologic Features of an Attenuated Onychomatricoma: A Novel Variant.

Onychomatricoma (OM) is a rare benign fibroepithelial nail unit tumor that remains frequently underrecognized, with evolving histopathologic criteria. Existing descriptions have largely focused on well-developed lesions, leaving the histopathologic features of smaller, localized lesions poorly characterized. We report an attenuated OM in a 45-year-old woman highlighting subtle but characteristic histopathologic features of OM, including a focal CD34-positive spindle cell population in the superficial submatrical dermis, matrical epithelial papillation, and focal serum-filled cavity formation within the nail plate. Compared with classic OM, these findings were more localized and less architecturally developed, while still retaining key diagnostic features. Improved recognition of these subtle features in attenuated lesions will facilitate earlier diagnosis, reduce misclassification, and refine clinicopathologic criteria for this important nail unit tumor.