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

Background: Longitudinal melanonychia (LM) is a common dermatologic finding in clinical practice with a broad differential diagnosis. Melanocytic activation is the most common LM etiology.

Objective: To investigate clinical and dermoscopic differences of benign LM based on Fitzpatrick skin type and in biopsied versus nonbiopsied patients.

Methods: A 10-year retrospective cohort of 248 benign LM cases at Weill Cornell Dermatology was identified and analyzed.

Results: 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%).

Limitations: Single-center retrospective design. Subungual melanoma and other benign LM etiologies were not analyzed. Only 18.95% of patients received a biopsy.

Conclusion: 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.