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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 H1-antihistamines or repeated exposures to natural sunlight., Conclusion: The term fixed solar urticaria is proposed for this peculiar type of solar urticaria.

Three patients with solar urticaria were treated with plasmapheresis. By intradermal injection of in vitro irradiated serum the existence of a circulating photoallergen was demonstrated in cases 1 and 2 but not in case 3. Plasmapheresis induced complete remission of solar urticaria in case 1 and transient improvement in case 2. In case 3, however, no beneficial effect was observed. It is suggested that some patients with solar urticaria, probably those with a circulating photoallergen, may benefit from plasmapheresis.

A technique is described to successfully treat patients with extreme sensitivity to UV electromagnetic wave lengths with photochemotherapy. Representative data from a patient with solar urticaria and two patients with persistent light reaction are given. Prior to treatment the threshold doses for UV-C, UV-B, and UV-A were determined. Photochemotherapy was performed with standard 8-methoxypsoralen-UV-A (PUVA) schedules. Initial treatments were very difficult because of the extreme UV-sensitivity in all patients. Once pigmentation was induced, PUVA-treatments were easy to perform. All patients became almost free of symptoms and were able, for the first time in years, to resume normal outdoor activities. Remission was long-lasting. Photochemotherapy is offered as a new effective means to alleviate the symptoms of disabling photodermatoses.

A 17-year-old male with solar urticaria is described. The action spectrum ranged from 400 to 520 nm. Wheals induced by visible light were inhibited by simultaneous or subsequent irradiation of the skin with UVA radiation. UVA irradiation prior to exposure to eliciting wavelengths revealed no inhibitory effect, nor was an inhibitory effect found by pre- or postirradiation of test sites with visible light longer than 530 nm. In vitro activation of the patient's serum by exposure to visible light induced wheal formation at the injection site. The wheal formed by in vitro-activated serum was suppressed only when the serum was exposed to UVA after, but not before irradiation with wavelengths of the action spectrum. This suggests that the inactivation of a photoallergen rather than of its precursor is the mechanism by which UVA exerts an inhibitory effect.

Although its exact mechanism remains unknown, evidence supports the immunologic nature of solar urticaria. On the basis of experimental findings in the literature and our own observations, a new concept of the pathogenesis and classification of solar urticaria is presented. We propose two types of solar urticaria: type I, IgE-mediated hypersensitivity to specific photoallergens, which are generated only in patients with solar urticaria, and type II, induction of IgE-mediated hypersensitivity to a nonspecific photoallergen, which is generated both in patients with solar urticaria and in normal persons.

The mechanisms by which tolerance is induced in solar urticaria were investigated in two patients whose eruptions were induced by wavelengths in the range 320–455 nm in one patient and 400–495 nm in another. Tolerance to radiation was induced by repeated exposures of the skin to the eliciting wavelengths of light. Weal and flare responses to intradermal injections of histamine and the histamine-releasing agent (codeine) were tinaltered in the tolerant skin when compared with adjacent normal skin. Intradermal injection of in vitro irradiated serum or plasma from the patients induced an urticarial reaction in the unexposed skin but not in tolerant skin and repeated injections induced tolerance to the eliciting radiation. The results suggest that tolerance is not due to exhaustion of the photoallergen in the skin, or to an increase of the mastcell degranulation threshold caused by exposure to ultraviolet radiation, or mast-cell mediator depletion, or histamine tachyphylaxis. It is likely that binding sites of IgE on mast cells remain occupied by the photoallergen during the state of tolerance, and that histamine release from mast cells is blocked. [ABSTRACT FROM AUTHOR]