High frequencies and co-existing of myositis-specific autoantibodies in patients with idiopathic inflammatory myopathies overlapped to rheumatoid arthritis.

A small proportion of patients with rheumatoid arthritis (RA) develop idiopathic inflammatory myopathies (IIM); however, the clinical and immunological characteristics of these patients have not been elucidated. In the present study, we evaluate the frequency of autoantibodies and the accompanying clinical features in patients with IIM overlapped to RA (IIM-RA) and in patients with IIM without RA. Twelve patients with IIM-RA were selected from 142 patients with IIM who were admitted to our hospital. Clinical and laboratory data, including autoantibody test results, were collected from patient medical records. Myositis-specific antibodies (MSAs) were analyzed by immunoprecipitation. Clinically, patients with IIM-RA were more likely to be male, to have polymyositis, and to be older at the time of IIM onset than patients with IIM without RA. Patients with IIM-RA had been treated for 2-25 years prior to the onset of IIM with more than two disease-modifying antirheumatic drugs (DMARDs). Patients with IIM-RA had a high frequency (75.0%) of positivity for MSAs, including anti-Jo-1, anti-PL-7, anti-PL-12, or anti-signal recognition particle (SRP) antibodies; anti-Jo-1 antibody was detected in 4 patients (33.3%). In addition, 2 out of 12 patients with IIM-RA were concurrently positive for two different MSAs, anti-Jo-1, and anti-PL-7 antibodies. In 3 other patients with IIM-RA, anti-Jo-1 antibody, or anti-PL-7 antibody was detected in serum samples collected 6-18 months prior to development of myositis. High frequency and coexistence of MSAs were detected in patients with IIM-RA. MSAs detected in patients with RA even without symptoms of myositis may indicate possible future development of myositis.