Subungual Melanoma

Longitudinal melanonychia encompasses several distinct conditions, including lentigo, nail matrix nevus, and subungual melanoma. Lentigo and nail matrix nevus represent benign lesions, while subungual melanoma is a malignant entity. Subungual melanoma arises from melanocytes within the nail apparatus and represents a specific subtype of cutaneous malignant melanoma. Most commonly, this form corresponds to acral lentiginous melanoma, a variant that typically develops on the palms and soles of the feet. First recognized by Boyer in 1834, subungual melanoma was later described in more clinical detail by Hutchinson in 1886. Hutchinson identified a hallmark feature known as the "Hutchinson sign," characterized by pigmentation extending from the nail onto the adjacent skin, a finding strongly associated with subungual melanoma. Also referred to as nail unit melanoma, subungual melanoma accounts for up to 3% of all melanoma cases in individuals with lightly pigmented skin. Among populations with darkly pigmented skin, the percentage rises significantly, accounting for up to 30% of melanoma diagnoses.[14] In approximately 65% of cases, nail melanoma initially presents as a dark, vertical pigmented band affecting a single nail.[15] These bands often exceed 3 mm in width and display proximal widening along with irregular lateral borders. Nail plate dystrophy frequently accompanies the pigmentation, serving as an additional clinical clue to the diagnosis.