Predictor of Subungual Melanoma against Benign Longitudinal Melanonychia: A Retrospective Cohort Study from Korea

BACKGROUND: Longitudinal melanonychia (LM) is a common clinical finding. Most cases of LM are benign, and a wait-and-see approach is preferred in the management of this condition. Nevertheless, it is important for clinicians to distinguish subungual melanoma (SUM) from other benign LMs. OBJECTIVE: To evaluate the demographic and clinicopathologic characteristics of LM in the Korean population and to identify the predictor of SUM against other benign conditions. METHODS: This was a single-center retrospective cohort study including patients who underwent nail biopsy for LM from January 2000 to May 2019. To identify the predictor of SUM, receiver operating characteristic (ROC) analyses was performed. RESULTS: A total of 68 cases of biopsy-proven LM were included in the analysis. Among the 68 cases, 8 were SUM. In univariable analysis, patients diagnosed with SUM were older (p=0.035) and had a longer disease duration (p=0.004). They also showed multicolor pigmentation of LM (p=0.022), a larger width of LM (p<0.001), and associated nail plate dystrophy (p=0.010) than patients diagnosed with benign conditions. In multivariable logistic regression, width of LM showed statistical significance (odds ratio, 1.083; 95% confidence interval, 1.018~1.153). ROC analysis suggested that an LM width >28% of the whole nail was the predictor of SUM (area under the curve=0.883; p<0.001). CONCLUSION: SUM has distinct demographic and clinical features. The width of LM can predict SUM against other benign LMs.