Pigmented lesions of the nail unit.

Longitudinal melanonychia originates from pigmented and/or melanocytic lesions of the nail unit. It may be a less-common entity encountered in dermatologic practice, but it is often a vexing one. Lesions occurring at this location present particular problems due to the unfamiliarity with clinical assessment, their relative inaccessibility, requiring more surgical finesse, and the lack of experience with histopathologic examination. Obtaining a specimen sufficient for interpretation is one of the main impediments to successful diagnosis in this setting. Most pigmented bands are benign, due to more common entities such as melanocytic activation, lentigo, and/or a nevus; however, deciding which ones are due to melanoma is of the utmost importance and can be difficult. Some examples of melanoma at this site are amelanotic, which are more challenging to recognize clinically, and usually lead to significant delays in diagnosis. In order to provide optimal patient care in this setting, it is very important that the physician has an understanding of the unique clinical, surgical, and pathologic issues relating to diagnosis of melanocytic neoplasms at this site, and there is communication between the clinician and the pathologist.