Background: Lymphocytic infiltration of the skin (LIS) is a disorder in which photosensitivity has been suspected but never proven.
Objectives: To carry out a systematic photobiological investigation in patients with LIS and to compare the photobiological features of LIS with those of other photosensitive disorders.
Methods: We performed provocative phototesting with ultraviolet (UV) A and UVB in 10 patients with active LIS.
Results: In all patients, UVA and/or UVB elicited abnormal papular phototest reactions resembling lesions of LIS both clinically and histologically. Lesions typically developed 3--6 days (mean +/- SD 100.8 +/- 20.9 h) after the first UV exposure.
Conclusions: This characteristic latency interval together with certain clinical features, i.e. onset in summer, predilection for the face and persistence of the lesions, indicate that LIS is a photosensitive disorder distinct from polymorphic light eruption but indistinct from lupus erythematosus (LE). Both our photobiological findings and the effective treatment with hydroxychloroquine in half of our patients strengthen the proposal that the two entities LIS and LE tumidus are identical. As diagnosis cannot be made by histological, immunofluorescence or laboratory criteria, provocative phototesting may be a diagnostic aid in this disorder.