Clinical and dermoscopic findings of benign longitudinal melanonychia due to melanocytic activation differ by skin type and predict likelihood of nail matrix biopsy

Longitudinal melanonychia (LM) is a common dermatologic finding in clinical practice with a broad differential diagnosis. Melanocytic activation is the most common LM etiology.To investigate clinical and dermoscopic differences of benign LM based on Fitzpatrick skin type and in biopsied versus nonbiopsied patients.A 10-year retrospective cohort of 248 benign LM cases at Weill Cornell Dermatology was identified and analyzed.Darker-skinned versus lighter-skinned patients had higher band width percentage (P = .0125), had lower band brightness (P < .001), had more band changes (P = .0071), and received more biopsies (P = .032). Biopsied (n = 47) versus nonbiopsied patients (n = 201) had less multidigit band involvement (P = .0008), higher band width percentage (P = .0213), lower band brightness (P = .0003), and more band changes (P < .0001). Darker skin types more often had brown versus gray coloration on dermoscopy (P = .0232). The mean band width percentage for all biopsied patients was 30.81% (range: 5.80%-100%).Single-center retrospective design. Subungual melanoma and other benign LM etiologies were not analyzed. Only 18.95% of patients received a biopsy.Darker versus lighter skin types more often present with darker and wider bands, present with brown versus gray coloration on dermoscopy, and receive more biopsies. Multi-institutional studies on LM are needed to determine nail matrix biopsy criteria in different skin types.