Objective: To investigate macroscopically and histopathologically the dermatological changes after Q-switched ruby laser (QRL) irradiation with different exposure doses in UVB-induced pigmentation in hairless dogs.
Methods: QRL irradiation with 3.0, 5.0 and 7.0 J/cm(2) was carried out on the UVB-induced spotty pigmentation in the skin of the hairless dog. Gross appearance was observed daily throughout this study. Histopathological examination was performed 1 day before QRL irradiation and 1 and 3 days and 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 14 and 16 weeks after QRL irradiation.
Results: Immediately after QRL irradiation, spotty pigmentation was removed. One week after QRL irradiation, re-epithelialization started from the margin of the irradiated sites. between 5 and 10 weeks after QRL irradiation, the skin color returned to normal and some portions showed recurrence of hyperpigmentation. Histopathologically, spotty pigmentation had a heavy deposition of melanin granules in the stratum basale, spinosum and corneum. One day after QRL irradiation, the skin showed destruction of melanin granules. Seven days after QRL irradiation, re-epithelialization began from the surroundings of the QRL-irradiated sites and the pilosebaceous units. The delayed process of re-epithelialization was dependent on the incident exposure dose with QRL. The repaired epidermis was devoid of melanin granules. By 5 weeks after QRL irradiation with 3.0 and 5.0 J/cm(2), the stratum basale and spinosum revealed a redistribution of melanin granules. In the sites of recurrent hyperpigmentation, the bases of the remaining hair follicles showed a notable increase in the reproduction of melanin granules. Melanin granules abundantly aggregated in the bottom portion of the nucleus in each epidermal cell.
Conclusion: These results revealed that hairless dogs were invaluable laboratory animals, which developed spotty pigmentation after successive UVB irradiation. In addition, UVB-induced spotty pigmentation in hairless dogs is useful for investigating the process of depigmentory treatment with QRL irradiation and recurrence of this lesion.