Longitudinal melanonychia: when to biopsy and is dermoscopy helpful?

Longitudinal melanonychia (LM) is a common presenting problem in general dermatology, and represents a diagnostic challenge to clinicians given its broad differential diagnosis that includes both benign and malignant entities. The decision of when a biopsy is required is incredibly challenging for dermatologists. Dermoscopy is a noninvasive technique that enhances the clinical evaluation of LM, and has demonstrated potential in improving the clinical decision making as to whether or not to biopsy LM. However, it is critical for clinicians to understand the limitations of dermoscopy, and that although it is able to add new criteria for the diagnosis of ungual pigmentation, it does not replace histopathologic diagnosis. Biopsy of the nail unit should be performed in any case where doubt based on the clinical evaluation exists.