Melanonychia: diagnosis and treatment

Melanonychia should be a term restricted to the presence of melanin in the nail unit. To be able to understand the process of melanin deposition in the nail plate, the nail apparatus and its melanocyte system are described. The different causes responsible for a black nail are reviewed, enabling the clinician to pick out those cases that are highly suspicious of being a malignant condition. Their differential diagnosis is also considered, with special attention to Hutchinson's sign. The second part of the article deals with the management of longitudinal melanonychia, including history, clinical examination, nail plate sampling, and when and how to perform a biopsy. Finally, pathology and subungual melanoma treatment are briefly reviewed.