Occurrence of polymorphous light eruption in lupus erythematosus.

Photosensitivity is a well-known manifestation of lupus erythematosus (LE). Since there are no strict criteria for photosensitivity, varying prevalence figures have been reported. Also, distinction from polymorphous light eruption (PLE) can be difficult. The purpose of this study was to characterize photosensitivity in more detail and to determine the occurrence of PLE in a series of well-documented LE patients. A questionnaire was answered by 337 LE patients seen at dermatology departments in Finland and Sweden, and 63 of the patients were invited for interview. According to the questionnaire, LE lesions were made worse by sunlight in 242 (72%) patients. Symptoms consistent with PLE were reported by 165 (49%) patients. Detailed personal interviews supported the results from the questionnaire, and revealed that PLE had started 2-45 years before the onset of LE in 23 of 37 patients with both diagnoses, and more than 7 years before in 18 of 37 (49%). PLE proved to be common in patients with both systemic and cutaneous LE. The two conditions may often coexist and, in about half of the cases, PLE preceded LE. These two diseases may share pathogenic factors. PLE might predispose to LE in a subgroup of PLE patients.