The Effects of UVA Irradiation on Depigmented Sites in the Skin of the Hairless Dog

Abstract

The effects of UVA irradiation on sites of Q-switched ruby laser (QRL) irradiation were grossly and histopathologically investigated, using UVB-induced spotty pigmentation in the skin of a hairless dog. There is no experimental evidence to date that UV irradiation stimulates melanocytes and melanogenesis in skin treated with QRL irradiation. The spotty pigmentation in the skin of the hairless dog was treated with QRL irradiation. The deleterious effects of UVA irradiation on the QRL-treated sites were then examined. Two weeks after the completion of UVA irradiation, pigmentation began from the surroundings of the QRL-treated sites and/or the remaining hair follicles. Pigmentation became more prominent and the recurrence of hyperpigmentation more frequent. Histopathologically, 1 wk after QRL irradiation, there were some vacuolated dihydroxyphenylalanine (DOPA)-positive melanocytes in which melanin granules were completely destroyed. At the QRL + UVA-treated sites, the number of DOPA-positive melanocytes increased significantly from 2 wk, peaking at 4 to 6 wk after completion of UVA irradiation. From 6 wk after UVA irradiation, there was a return to a normal distribution of DOPA-positive melanocytes. In areas of recurrence of hyperpigmentation, melanin granules aggregated at the bottom of the nucleus of each epidermal cell. The lower portions of hair follicles produced an excess of melanin granules. UVA irradiation had deleterious effects on the QRL-treated sites and caused a recurrence of spotty pigmentation. Hairless dogs are useful laboratory animals for evaluating gross and histopathological changes in pigmented lesions treated with QRL irradiation.