Light and electron microscopic investigation of the process of healing of the naevus of Ota by Q-switched alexandrite laser irradiation

Melanocytes in the naevus of Ota were destroyed by irradiation using the Q-switched alexandrite laser. This laser is highly selective and highly absorbed by melanosomes. Other cells and tissue components of the dermis remained almost intact. Melanosomes were vaporized or fragmented to subelectron microscopical size, or degenerated. If the irradiated energy was sufficient, melanocytes vanished and large vacuoles several times the size of dermal melanocytes formed at the sites. If it was too weak, dermal melanocytes were also vaporized, but vacuoles formed within them. Nuclei were no longer discernible. Following irradiation macrophages infiltrated the irradiated areas and scavenged degenerated melanosomes and cellular debris. Thus, discoloration of the skin was markedly reduced. Although a few melanocytes and melanophages remained, pigmentation cleared to a satisfactory level. Melanocytes and keratinocytes were also injured in the epidermis; however, the epidermis recovered completely. No scarring was observed.