Effect of Q-switched Alexandrite laser irradiation on epidermal melanocytes in treatment of Nevus of Ota

To investigate injury to epidermal melanocyte by Q-switched Alexandrite laser Methods Multiple biopsies were performed on 5 patients with nevus of Ota from before irradiation to 1 year after irradiation Fourteen specimens were obtained for light microscopy, and 17 for transmission electron microscopy Results Melanosomes in epidermal melanocytes were both smaller in size and fewer in number than those in dermal melanocytes Immediately after irradiation, focal extracellular vacuoles of the basal layer could be observed under light microscopy Most epidermal melanocytes underwent mild or moderate injury in the form of vacuolated melanosomes, swollen mitochondria, dilation of endoplasmic reticulum, and expansion of extracellular space, retaining intact cell membranes Normal structures were restored 5 months to 1 year after irradiation, with no depigmentation or hyperpigmentation as seen by light microscopy Conclusion Injury of melanosomes in epidermal melanocytes is reversible