Melanonychia descriped as brown or black linear pigmentation of the nail unit. Melanonychia commonly presents as pigmented band arranged lengthwise along the nail unit, and this presentation is known as longitudinal melanonychia (LM) or melanonychia striata.
The most important cause of melanonychia is subungual melanoma, but a variety of other causes includes :physiologic longitudinal melanonychia, systemic disorders, trauma, inflammatory disorders, fungal infections, drugs, and benign melanocytic hyperplasias.