Prurigo pigmentosa. Case report with an electron microscopic observation.

Prurigo pigmentosa is an inflammatory dermatosis characterized by pruritic, reddish, papular lesions and gross reticular pigmentation that occurs mainly on the trunk. Nearly 100 cases have been reported in Japan to date. We describe a patient with this condition who responded well to dapsone. An electron microscopic study of the reddish papular lesion showed marked intercellular edema and evidence of cellular injury of the basal cells. Direct immunofluorescence was negative. We stress that this condition is a distinct clinical entity, histologically characterized by a lichenoid tissue reaction as proposed by Pinkus, although it is little known outside Japan.