Melanomas of the nail matrix are concealed beneath the proximal nail fold and the proximal part of the nail plate.

They originate from the nail matrix at this location, which extends distally to the level of the lunula.

Fortunately, if a melanoma of the nail matrix is pigmented, the pigment in the stratum corneum of the matrix will be incorporated into the growing nail plate, as it is derived from the structure, and will appear as a longitudinal stripe; longitudinal melanonychia.

Hutchinson’s sign, which is pigmentation of the proximal or lateral nail folds, is a useful additional clue, although not specific to melanoma.