Polychromatic phototest as a prognostic tool for polymorphic light eruption

Background: Diagnosis of polymorphic light eruption (PLE) is based on the p atient's history, the morphology of the lesions and the results of phototes ting, Skin lesions of PLE can be provoked by repetitive UVB or UVA irradiat ion. However, about 20% of the patients with PLE have negative phototests. As 24% of the patients with PLE go into remission, it was of interest to se arch for a link between the results of the phototests and the evolution of the photodermatosis. Methods: Forty patients with PLE were recruited and repetitive phototests w ere performed. To ensure a good reproducibility of the phototests, one to t hree phototests were performed on each patient at different stages of the d isease including the period when the PLE had gone into remission. Results: Except for one patient, there was a good reproducibility of the re petitive polychromatic phototests: in each patient, the tests remained posi tive or negative throughout the disease. After long-term follow-up, two dif ferent subgroups were identified: 30 patients with active PLE and 10 patien ts in remission. There were no clinical differences between these two group s apart from the age of onset and the clinical lesions of the PLE, PLE bega n at an earlier age in the patients in remission and presented mainly with a plaque-type eruption. In total, 52.5% of the patients had at least one po sitive polychromatic phototest, Phototests were positive only in patients w ith active disease. All the patients in remission had negative phototests. Conclusions: Repetitive phototests could be a prognostic marker for PLE. Tw o subtypes of PLE were identified on the basis of phototest results: the be nign form of PLE with negative phototests, which tends to go into remission , and the more severe and more chronic PLE, with positive phototests.