A Case of Onychopapilloma Presenting Brown Streaks Mimicking a Longitudinal Melanonychia: Histopathological Findings of Serial Transverse Sections and Literature Review

Abstract

Onychopapilloma (OP) is a rare benign tumor of unknown etiology that develops in the distal nail matrix and nail bed epithelium of the fingers and toes, with hyperkeratosis and papillomatosis formation. The changes in the nail plate are red streaks and subungual hyperkeratosis, but there are also white and brown streaks in addition to red. We have now encountered a case of OP with brown streak-like findings. Histopathological examination of the cross-section revealed papillomatosis and subungual hyperkeratosis due to the extension of the epidermal process from the nail matrix to the nail bed. Immunostaining of the brown streaks showed hemosiderin. There have been few reports of pathological examination of serial cross-section specimens in the past, and we hope that this will help elucidate the true nature of this disease.