Melanonychia is brown or black discoloration of a nail. It may be diffuse or take the form of a longitudinal band. Below are examples of Benign longitudinal melanonychia.
Who is at risk of melanonychia?
Melanonychia can present in individuals of all ages, including children, and affects both sexes equally. It is more prevalent in people with skin of color.
- Nearly all Afro-Caribbean people will develop black-brown pigmentation of the nails by the age of 50.
- Melanonychia affects up to 20% of Japanese people.
- White-skinned people are less commonly affected.
Melanonychia can also be associated with genetic disorders, injury, medications, nutritional deficiency, endocrine disease, connective tissue disease, inflammatory skin disease, a local tumor, or nail infection.
What causes melanonychia?
The nail plate is a hard, translucent structure made of keratin. It is not normally pigmented. Melanocytes typically lie dormant in the proximal nail matrix where the nail originates. Melanin is deposited into the growing nail when melanocytes are activated, resulting in a pigmented band — this is longitudinal melanonychia.