Leukocytoclastic vasculitis in urticaria induced by ultraviolet irradiation.

A 35-year-old woman would develop urticarial lesions over one to four hours after irradiation with sunlight or artificial ultraviolet radiation. Lesions could persist for days before resolving. Although lesions were morphologically typical of solar urticaria, their evolution and resolution were both much slower than expected. Histologically, the lesions showed leukocytoclastic vasculitis. This unexpected finding suggests the possibility that there may be novel mechanisms involved in the pathogenesis of some cases of solar urticaria.