Melanonychia is a brown to black colour of the nail. It is due to the presence of melanin in the nail plate. It is caused by activation or benign/malignant proliferation of nail matrix melanocytes.
When the pigmentation involves the whole nail it is called total melanonychia. When it is banded it is either transverse or longitudinal. Longitudinal melanonychia is the commonest form. The commonest cause of longitudinal melanonychia in adults is racial variation (see photo), trauma has been implicated in their development. The commonest cause in children is benign melanocytic hyperplasia.
Longitudinal melanonychia of a single nail deserves biopsy in adults as a high degree of suspicion is required if subungual melanoma is not to be missed. In children it is usually benign in nature and can be followed.
Racial longitudinal melanonychia
This page was last updated in April 2013.