Longitudinal subungual acanthoma: one denomination for various clinical presentations

Background Benign subungual proliferation of the distal nail matrix and bed such as longitudinal keratosis, seborrhoeic keratosis or onychocytic matricoma should belong to a single spectrum of diseases. Objective This article intends to demonstrate clinically and histologically the different facets of Nail unit longitudinal acanthoma. Methods We report three new cases that present as a longitudinal melanonychia with thickening of the nail plate in two of them and as leukoxanthonychia in the third one. We compared them with the two original cases we described in 1999, reminiscent of seborrhoeic keratosis and all the new cases published since then. Results We therefore consider that all these tumours belong to a single spectrum of diseases, we have called ‘nail unit longitudinal acanthoma’ which describes a histopathological process. The distinct clinical features of these tumours, melanonychia or leukoxanthonychia may be linked to their variable anatomic locations in different zones of the nail unit.