Abstract
Melanonychia due to melanocyte activation may present as a longitudinal, horizontal, or diffuse band of gray, brown, or black pigmentation extending from the nail matrix to the free margin of the nail plate.Hypermelanosis is responsible for the majority of adult cases of longitudinal melanonychia, especially in patients with darker skin phototypes.Hypermelanosis is defined by increased melanin production and pigmentation of the nail matrix epithelium and nail plate without an increase in the number of melanocytes on histological examination.Most etiologies of hypermelanosis are benign and can be identified by a thorough history and physical examination.Failure to identify a cause of melanonychia should raise concern with regard to nail apparatus melanoma and requires histopathological evaluation.