Dermatoscopy of combined blue nevi: A multicenter study of the International Dermoscopy Society

BACKGROUND: Combined blue nevi may mimic melanoma and are relatively often biopsied for diagnostic reasons.OBJECTIVE: To better characterize combined blue nevi and to compare it with melanoma.METHODS: We collected clinical and dermatoscopic images of 111 histologically confirmed combined blue nevi and contrasted their dermatoscopic characteristics with 132 partly blue colored melanomas. Furthermore, we compared the accuracy of human experts using pattern analysis with a computer algorithm based on deep learning.RESULTS: Combined blue nevi are usually flat or slightly elevated and, in comparison to melanoma, more frequent on the head and neck. Dermatoscopically, they are typified by a blue structureless part in combination with either brown clods (n=52, 46.8%), lines (n=28, 25.2%), or skin-colored or brown structureless areas (n=31, 27.9%). In contrast to melanoma, the blue part of combined blue nevi is more often well defined (18.9% versus 4.5%, p<0.001) and more often located in the center (22.5% versus 5.3%, p<0.001). Melanomas are more often chaotic (OR: 28.7, 95% CI: 14.8-55.7, p<0.001), have at least one melanoma clue (OR: 10.8, 95% CI: 5.2-22.2 p<0.001) in particular white lines (OR: 37.1, 95% CI: 13.4-102.9, p<0.001). Using simplified pattern analysis (chaos and clues), two raters reached sensitivities of 93.9% (95% CI: 88.4-97.3%) and 92.4% (95% CI: 86.5-96.3%) at corresponding specificities of 59.5% (95% CI: 49.7-68.7%) and 65.8% (95% CI: 56.2-74.5%). The human accuracy with pattern analysis was on par with a state-of-the-art computer algorithm based on deep learning that achieved an area under the curve of (0.92, 95% CI: 0.87-0.96) and a specificity of 85.3% (95% CI: 76.5-91.7%) at a given sensitivity of 83.6% (95% CI: 72.5-91.5%).CONCLUSION: Combined blue nevi usually lack melanoma clues, in particular white lines. The accuracy of pattern analysis for combined nevi is acceptable and histopathologic confirmation may not be necessary in exemplary cases.