The frequency of myositis-associated and myositis-specific autoantibodies (AAb) was compared in 51 s-IBM patients and a population control group. Non-organ specific AAb (ANA, anti-Ro52, anti-Ro60, anti-La, anti-RNP) but not anti-thyroid peroxidase, anti-tissue transglutaminase or myositis-specific antibodies, were more frequent in s-IBM patients, and 14/51 (27%) had another autoimmune disease (Sjögren's syndrome, thyroiditis, psoriasis, vitiligo). The presence of AAb did not correlate with carriage of HLA-DRB1*0301, but there was a negative correlation between ANA/anti-Ro52 and carriage of HLA-DRB1*1301. The findings in this cohort confirm that patients with sIBM do not show evidence of a muscle-specific humoral immune process but have an increased frequency of non-organ specific AAb and other autoimmune disorders.
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