Abstract: Objective To investigate the effect of Q-switched Alexandrite laser irradiation on the dermal melanocytes in nevus of Ota. Methods Multiple biopsies were taken in 4 patients with nevus of Ota before and after laser irradiation, altogether 11 biopsies for light microscopic examination and 14 biopsies for transmission electron microscopic examination. Results Immediately after laser irradiation, the dermal melanocytes were destroyed, the melanosomes were disrupted like vacuoles with the formation of intradermal round vacuoles; the epidermis, however, remained intact. Three months to 1 year after irradiation, the disrupted melanosomes and the cell debris were scavenged mainly by macrophages. Dermal melanocytes gradually decreased in number. No fibrosis was found. Conclusion The dermal melanocytes in nevus of Ota can be selectively destroyed by Q-switched Alexandrite laser, without any gross injury.

Key words: Nevus of Ota, Lasers, Melanocytes, Microscopy, electron