[Bullous localization of a lupus erythematosus induced by radiotherapy].

Introduction: Connective diseases induced or exacerbated by radiotherapy are not frequent. We report a particular erosive erythematosus lupus with lesions in the precise distribution of radiation therapy given for a breast cancer.

Observation: An 80 year-old woman presented with painful erosive skin lesions of her breast which had been treated by irradiation 9 years before. The patient also had rheumatoid arthritis. A skin biopsy showed keratinocyte necrosis, acantholysis and a dermal lymphocytic infiltrate under the basal cell layer. Direct immunofluorescence showed granular deposition of IgG, IgM and C3 along the basal cell layer. Antinuclear antibodies were positive at a titre of 1: 1,000. Erythematosus lupus diagnosis was established and annular lesions secondarily appeared on her neck, back, and arms. A treatment with hydroxychloroquine and topical corticosteroïds was effective in 3 months.

Discussion: The unusual erosive lesions and their localization on a previously irradiated site suggest the role of X-rays in our observation, despite their late appearance after radiotherapy. Radiotherapy and erythematosus lupus affect the same target structures (basal cells and small dermal capillaries) and could have additive effects. The presence of rheumatoid arthritis in the past medical history may have exaggerated this complication.