Retrospective single-center study evaluating clinical and dermoscopic features of longitudinal melanonychia, ABCDEF criteria, and risk of malignancy.

BACKGROUND: Longitudinal melanonychia (LM) is a common finding in clinical practice; however, it has a broad differential diagnosis, including subungual melanoma (SUM), which can be difficult to distinguish clinically from benign conditions. OBJECTIVE: To identify clinical and dermoscopic features that distinguish histopathologically diagnosed SUM from benign LM and to evaluate the validity of the ABCDEF criteria among patients on whom a biopsy was performed. METHODS: Retrospective cohort study of consecutive patients who underwent nail matrix biopsy for LM at a single center from January 2011 to November 2017. RESULTS: A total of 84 cases in which biopsy was performed (8 cases of SUM and 76 benign) were included in the analysis. The patients with SUM were younger (P = .011), had their melanonychia longer (P = .017), and presented with a wider band (P = .002) and greater width percentage (P < .001) than patients with benign LM did. The number of ABCDEF criteria met did not differ between the groups. LIMITATIONS: Retrospective single-center study; patients who did not undergo biopsy could not be studied. CONCLUSIONS: In the cases of LM in which biopsy was performed, SUM usually presented with a wider band and greater width percentage than benign LM did. The number of ABCDEF criteria met was not different between the groups. Because many of the clinical and dermoscopic signs were less consistent, biopsy should be performed in cases with any concerning band, especially in those with width percentage higher than 40%.