WHAT IT IS: Longitudinal melanonychia refers to a pigmented line that runs vertically along the nail. It is caused by deposition of melanin from melanocytes in the proximal nail matrix.
HOW IT IS IDENTIFIED: These black or brown lines may occur in some or all of the fingernails. The lines may be diffuse and light in shade or be darker and form a longitudinal band. They can vary in width and position. The lines in the images are mainly centrally positioned but they may also occur more laterally. Melanonychia is a normal variant in up to 90% of black people. It may however, represent a subungual melanoma (melanoma of the nailbed). Melanomas typically have a wide (>3mm), new and changing band in a single nail.