Nail (subungual) melanoma is a rare subtype of acral lentiginous melanoma that arises in the nail unit due to malignant melanocytic hyperplasia in the nail apparatus. Nail apparatus melanoma is a more frequently represented melanoma in darker skin colors, such as individuals of African (15%-20% of all melanomas), Native American (33%), Hispanic, and Asian (10%-30%) descent, than in individuals of Northern European descent (1%-3%). The diagnosis is challenging and often delayed (average depth at the time of diagnosis is 3.5-4.7 mm). Therefore, it can carry significant mortality and morbidity.

Most nail melanomas arise in the nail matrix. Melanoma arising from the epithelium of the nail bed or surrounding epidermis is rare. Two-thirds of cases of nail melanoma present as longitudinal melanonychia. More advanced cases present as a subungual mass with associated onychodystrophy. Hutchinson sign (extension of pigment to the nail folds) is another sign of advanced nail melanoma. Up to a quarter of all subungual melanoma cases are amelanotic (nonpigmented), making early diagnosis even more difficult.

The thumb is the most frequently involved digit, followed by the hallux and then the index finger. Subungual melanoma most commonly affects adults ages 50-70 years. There is no male or female predilection.

Nail melanoma is exceedingly rare in children. There have been rare case reports of nail melanoma in pediatric patients of all skin types. Pediatric cases similarly present as longitudinal melanonychia and most often involve the thumb.