Polymyositis as a manifestation of chronic graft‐versus‐host disease

Objective. Chronic graft-versus-host disease(GVHD) after haematopoietic stem cell transplantation (HSCT) has similarities to some idiopathic autoimmune diseases, including polymyositis. To investigate the relationship between chronic GVHD and idiopathic myositiswe conducted a detailed analysis of all cases of myositisoccurring in a large series of HSCT patients. Methods. We conducted a retrospective chart review of all cases of myositisthat developed in 7161 patients who underwent HSCT at the Fred Hutchinson Cancer Research Center between 1969 and 1999. Results. Among 1859 individuals who developed chronic GVHD, 12 developed myositis. No patients developed myositiswithout chronic GVHD. Myositiswas first identified between 7 and 55 months after transplantation. In histopathology, electromyography, laboratory values and response to immunosuppressive therapy, the cases resembled idiopathic polymyositis. Autoantibodies were found in eight cases. Conclusions. Myositisin the chronic GVHD population occurred with an incidence higher than expected by chance, suggesting that muscle may be a target tissue for chronic GVHD. Recent studies have implicated allogeneic cells persisting after maternal-fetal cell transfer in selected autoimmune diseases, including myositis. This report lends support to the possibility that both idiopathic myositisand chronic GVHD-related myositiscould involve allo-autoimmune responses.