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.