Clinicopathologic study of solar dermatitis, a pinpoint papular variant of polymorphous light eruption in Taiwan, and review of the literature

Background/Purpose: A mild, micropapular eruption previously coined as " solar dermatitis" on the extensor of the forearm is a common form of photodermatitis in Taiwan. This study aimed to investigate the clinicopathologic findings of " solar dermatitis" , the micropapular type of photodermatitis. Methods: We characterized the features of this photodermatitis by retrospectively reviewing and analyzing all such cases in a medical center in Southern Taiwan diagnosed during October 1988 to November 2010. Results: A total of 34 Taiwanese patients, all with Fitzpatrick skin type III-IV, were included (M:F = 1:1; mean age = 33.5 years; range = 9-62 years). Patients typically presented numerous, monomorphous, pinhead-sized micropapules on the extensor of the forearm after a recent, more intense sun exposure. The rash was often mildly pruritic and recurred in the summer, but usually resolved in a few days after sun protection and topical corticosteroid treatment. Reduced minimal erythema dose to UVB was noted in 2 of the 5 patients tested. Histopathologic examination (. n = 10) revealed a mild spongiotic dermatitis. Conclusion: The clinicopathologic findings of the " solar dermatitis" closely resembled those of the pinpoint papular variant of polymorphous light eruption (PP-PMLE) affecting African Americans and Asians in Singapore. PP-PMLE, micropapular light eruption in Japanese, summertime actinic lichenoid eruption in Indians and the present photodermatitis might represent a common, micropapular variant of PMLE affecting darker skin populations.