Onychopapilloma is a rare benign tumour of the nail apparatus (nail bed and distal nail matrix) of unknown etiology. It has no predilection for sex of ethnicity, but is more commonly reported in middle-aged and older adults.

Clinically, the lesion presents as longitudinal erythronychia affecting a single nail (with melanonychia and leukonychia much less commonly). The overlying nail changes develop from a well-circumscribed warty keratinized tumour that grows under the nail plate and which may become visible by extending beyond the free edge of the nail plate. The tumour may also cause onycholysis, splinter hemorrhages, longitudinal ridging or even longitudinal splitting of the nail plate.

The clinical picture is not specific to onychopapilloma, so a nail biopsy is required to differentiate it from other benign (glomus tumour, verruca, lichen planus) or potentially malignant (bowen’s, melanoma, BCC, SCC) lesions in the differential diagnosis.

Histopathology is also not entirely specific, but benign acanthotic keratinocytes with papillomatosis and hyperkeratosis support the diagnosis in the right clinical context. Longitudinal excision of the affected proximal nail matrix and associated nail bed is curative.