Melanonychia is a black or brown pigmentation of the normal nail plate, and may be present as a normal finding on many digits in black patients, as a result of trauma, systemic disease, or medications, or as a postinflammatory event from such localized events as lichen planus or fixed drug eruption.[1]:790[2]:665
There are two types, longitudinal and transverse melanonychia.[2]:671 Longitudinal melanonychia may be a sign of subungual melanoma (Acral lentiginous melanoma),[3] although there are other diagnosis such as chronic paronychia, onychomycosis, subungual hematoma, pyogenic granuloma, glomus tumour, subungual verruca, mucous cyst, subungual fibroma, keratoacanthoma, carcinoma of the nail bed, and subungual exostosis.