Polychromatic phototest as a prognostic tool for polymorphic light eruption

Diagnosis of polymorphic light eruption (PLE) is based on the patient's history, the morphology of the lesions and the results of phototesting. Skin lesions of PLE can be provoked by repetitive UVB or UVA irradiation. 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 search for a link between the results of the phototests and the evolution of the photodermatosis.

Forty patients with PLE were recruited and repetitive phototests were performed. To ensure a good reproducibility of the phototests, one to three phototests were performed on each patient at different stages of the disease including the period when the PLE had gone into remission.

Except for one patient, there was a good reproducibility of the repetitive polychromatic phototests: in each patient, the tests remained positive or negative throughout the disease. After long-term follow-up, two different subgroups were identified: 30 patients with active PLE and 10 patients in remission. There were no clinical differences between these two groups apart from the age of onset and the clinical lesions of the PLE. PLE began 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 positive polychromatic phototest. Phototests were positive only in patients with active disease. All the patients in remission had negative phototests.

Repetitive phototests could be a prognostic marker for PLE. Two subtypes of PLE were identified on the basis of phototest results: the benign form of PLE with negative phototests, which tends to go into remission, and the more severe and more chronic PLE, with positive phototests.