No abstract

Acquired pigmented lesions of the nail have a variety of clinical presentations and etiologies, including subungual melanoma. Previous work has suggested that melanocytes in the distal nail matrix most often develop into subungual melanoma, although there have been reports of it originating from the proximal nail matrix, hyponychium, or paronychium. 1-3 Many argue that pigmented melanomas, which excludes amelanotic melanoma, can originate directly from melanocytes in the nail bed. 1,2 However, a search of the literature does not reveal any evidence of a pigmented melanoma being diagnosed while isolated to the nail bed. We therefore hypothesized that if pigmented melanomas arise from the nail matrix and not the nail bed, then melanocytes are probably isolated to the nail matrix and absent from the nail bed. We performed a qualitative histologic analysis of nail units from cadaveric human tissue to detect the location of melanocytes within the nail unit. Using 4 different melanocyte-specific stains, we show that melanocytes are present in the nail matrix and largely absent in the nail bed. Hematoxylin-eosin staining of human cadaveric nail unit, sliced longitudinally. The box in A indicates the enlarged area shown in B, and the box in B indicates the enlarged area shown in C. Proximal is on the left-hand side of the images, and distal is on the right-hand side.