Clinical and histological responses of congenital melanocytic nevi after single treatment with Q-switched lasers

Background: Laser irradiation of congenital melanocytic nevi is a controversial treatment. Recurrence of lesions after laser treatment appears to be the rule, and the effects of laser irradiation on cellular biological behavior and the possible mutagenic responses of nevomelanocytes that have received nonlethal doses of irradiation are still unclear. Without treatment, there is an increased potential for malignant degeneration over a life-time. The purpose of this study was to examine the effects of Q-switched lasers on congenital nevi and to explain the mechanism(s) behind the response of the nevi to laser treatment. Five congenital nevi were divided into 3 equal parts: 1 part was treated with the Q-switched ruby laser at a wavelength of 694 nm, 1 part was treated with the Q-switched neodymium:YAG laser at a wavelength of 1064 nm, and 1 part was left untreated to serve as control. At intervals ranging from 3 days to 3 months after laser irradiation, the lesions were excised and evaluated by routine staining. This clinical study was conducted entirely at the Massachusetts General Hospital Dermatology Laser Center, Boston, Mass. Observations: Both the superficial and the deep portions of the congenital melanocytic nevi were affected by the 2 lasers, as evidenced by macroscopic inspection as well as microscopic evaluation. However, the Q-switched laser treatment did not destroy all nevomelanocytes, particularly in the deeper, less pigmented portions of the lesions. Conclusions: Both the Q-switched ruby laser and the neodymium:YAG laser often removed only the superficial portion of the congenital melanocytic nevi. The Q-switched ruby laser (694 nm) appeared to be more effective in removing nevomelanocytes than the Q-switched neodymium:YAG laser (1064 nm).