Prurigo pigmentosa: a possible mechanism of action of sulfonamides.

The patient described here had all the clinical features (itchy red papules and reticular pigmentation) as well as the histological findings (lichenoid tissue reactions) of prurigo pigmentosa, a little-known disorder of unknown etiology, and responded well to sulfamethoxazole treatment. In order to investigate the mode of action of this drug and thus the underlying pathogenesis of this dermatosis, the effect of sulfamethoxazole on the production of oxygen intermediates (OIs) was examined both in the cell-mediated system and in the xanthine-xanthine oxidase system. It was found that therapeutic doses of the drug significantly reduced the hydroxyl radical levels, one of the most potent oxidants that might cause tissue injury. These findings suggest the possibility that OIs produced by infiltrated cells are involved in the inflammatory process of prurigo pigmentosa and that sulfonamides exert their anti-inflammatory effects by affecting OI generation which results in protection against lichenoid tissue reaction.