Fixed solar urticaria

Background : Three unusual cases of solar urticaria limited to fixed skin sites are described. Objective : Our objective was to study the clinical course and several therapeutic regimens for fixed solar urticaria. Methods : Phototesting and in vitro activation of a plasma factor were performed. Results: Wheals in a patchy pattern were strictly localized to the same circumscribed skin areas; they were reproducible in their pattern and location by irradiation. The action spectra ranged from 320 to 700 nm, 320 to 585 nm, and 400 to 560 nm. In one patient inhibition was found by wavelengths between 280 and 320 nm. Intradermal injection of the patients' plasma activated by in vitro irradiation induced wheals only in the affected skin sites. The patients showed a good therapeutic response to H 1 -antihistamines or repeated exposures to natural sunlight. Conclusion : The term fixed solar urticaria is proposed for this peculiar type of solar urticaria.