Melanonychia is a black or brown pigmentation of the normal nail plate, and may be present as a normal finding on many digits in Afro-Caribbeans people.

A wide, deeply pigmented band with irregular lines and pigmented extension onto the periungual tissues is a sign for melanoma.

  • Unusual multiple lines are observed. Melanonychia is mostly benign, but if there are many irregular lines at this level, a biopsy may be considered.
  • Muehrcke's lines
  • Brown banding
References Melanonychia: Etiology, Diagnosis, and Treatment 32055501 
Melanonychia is a very worrisome entity for most patients. It is characterized by brownish black discoloration of nail plate and is a common cause of nail plate pigmentation. The aetiology of melanonychia ranges from more common benign causes to less common invasive and in situ melanomas. Melanonychia especially in a longitudinal band form can be due to both local and systemic causes.
 Melanonychia – Clues for a Correct Diagnosis 32064201 
Melanonychia represents a brown to black discoloration of the nail plate that may be induced by benign or malignant causes. Two main mechanisms are involved in the appearance of melanonychias, i.e., melanocytic activation and melanocytic hyperplasia.