Solar urticaria: A consideration of the mechanism of inhibition spectra.

BACKGROUND

Solar urticaria is a rare disorder characterized by pruritus, erythema and wheal upon sunlight exposure. Inhibition spectra (IS), which prevent wheal formation, have been found mainly in Japanese patients and lie mostly in longer wavelengths than the action spectrum (AS). The exact mechanism of AS and IS has not been clarified.

PATIENTS AND

METHODS

To elucidate the mechanism of AS and IS, we conducted photobiological studies including in vitro irradiated serum injection tests and measurements of plasma histamine levels in 3 patients with IS.

RESULTS

All patients had AS ranging between 400 and 490 nm and IS ranging between 520 and 610 nm. A wheal reaction appeared soon after the termination of IS irradiation. The patients developed no wheal or erythema upon intradermal injection of preirradiated serum. Plasma histamine levels were not elevated during irradiation with slide projector light, but marked elevation of histamine was observed when wheals developed after the termination of inhibitory irradiation.

CONCLUSION

These results suggest that the IS in our cases might inactivate photoallergens produced by AS and, additionally, stabilize mast cell degranulation.