Q‐switched ruby laser irradiation on spotty pigmentation in the skin of the hairless dog

Abstract

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/cm2 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/cm2, 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.