Pregnancy Associated Atypical Onychopapilloma: A Novel Presentation of an Emerging Entity in Dermatopathology.

Onychopapilloma (OP) is a benign nail unit tumor of the distal nail matrix and nail bed that typically presents as solitary longitudinal erythronychia with distal subungual hyperkeratosis and focal onycholysis. Atypical OP is a newly recognized and evolving concept in dermatopathology. Herein, we present a histopathologically-proven atypical OP with a classic clinical appearance that developed during pregnancy. A 37-year-old Gravida two Para one woman presented with a red longitudinal band on the left thumbnail that appeared during the first trimester of an uncomplicated pregnancy. The lesion was asymptomatic; however, it was gradually increasing in size, prompting a longitudinal excisional biopsy of the lesion post-partum. Histopathologic evaluation of the nail unit revealed common features of an OP, including acanthosis and papillomatosis of the nail bed with focal matrix metaplasia. There were focal areas of cytologic atypia and mitotic figures with corresponding increased suprabasilar Ki-67 expression. The tumor was excised with Mohs micrographic surgery in one stage, and the resulting defect healed with secondary intention. No recurrence was observed at 6-month follow-up. This case expands the current literature on histopathologically-proven atypical OP and describes the novel occurrence during pregnancy.