Longitudinal Melanonychia Biopsy: What Not to Do.

The nail matrix biopsy is an important technique in confirming or excluding a diagnosis of melanoma in a patient with longitudinal melanonychia. Dermatologists are the first-line diagnosticians for these pigmented lesions of the nail unit, however, for different reasons, some are reluctant to perform a nail biopsy. This case demonstrates how a poor biopsy technique resulted in a misdiagnosis in a patient with melanoma in situ.