Difference in distribution of malignant melanoma and melanocytic nevus in the palm and finger.

We conducted a study to try to plot the lesions of melanocytic nevus and malignant melanoma on the palm and fingers, and compared them to identify the different distribution pattern of both lesions. Data on 8 patients with melanomas (4 male and 4 female) and 26 patients with melanocytic nevus (6 male and 20 female) of palm and finger pulp who visited Wakayama Medical University Hospital between 1986 and 2018 was retrospectively collected. We found that all of the 8 lesions of melanoma were located on the finger pulps and distal to the 'distal transverse crease' of the palm, and that melanomas were not present proximal to the transverse crease. On the other hand, melanocytic nevus was present in the proximal area to the distal transverse crease of the palm more frequently than melanomas (50.0% vs. 0%), and there was statistically significant difference (p = 0.011 by Fisher's exact probability test). From these observations, our findings may reveal the contribution of mechanical stress to the cause of palmar melanoma, and may facilitate clinical differentiation between malignant melanoma and melanocytic nevus by the localization. Further studies with increased number of patients are needed to validate the finding.