Melanonychia: hyperpigmented longitudinal streaks

This 20-year old boy man had presented with slowly progressing brown colored longitudinal streaking of the finger nails for over three years.

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.