Background: Actinic prurigo, as idiopathic skin reaction involving light-exposed areas, was first described in American Indians. Actinic prurigo was early considered to be a particular form at polymorphous phototoxicity, but can be identified as a specific entity on the bases of clinical features and epidemiological characteristics.
Case reports: Three children in the same family developed photosensitive reactions early in childhood with characteristic polymorphous and persistent eczema-like or papulo-nodular pruriginous lesions which predominated in light-exposed areas and appeared several hours after exposure to sun. The lesions persisted during the winter season. The lesions followed a chronic course but tended to improve at puberty. Clinical laboratory tests, serum and urine porphyrin levels and antinuclear factors were normal. Histology and photobiology explorations gave non-specific results.
Discussion: These observations have three points in common with actinic prurigo observed in American Indians. HLA typing showed that our three patients, as in white patients in Great Britain, had a significant association with a specific HLA DR1 subtype: DRB1*0407. This DRB1*0407 alleles could play a role in initiating the immune response to a light-induced peptide antigen. This particular genetic predisposition, if confirmed in other studies, would be an additional argument for distinguishing actinic prurigo as a specific polymorphous phototoxicity entity.