Inflammatory myopathies are a heterogeneous group of immune-mediated diseases that involve skeletal muscle as well as many other organs. The classification of inflammatory myopathies has been based on clinical diagnoses, pathological diagnoses, and autoantibodies, independently. Antisynthetase syndrome, characterized by myositis, interstitial lung disease, skin rash, arthropathy, and Raynaud phenomenon, is a clinical entity based on the presence of aminoacyl transfer RNA synthetase (ARS) antibodies in patients’ serum. A cohort study of muscle biopsy entitled “Integrated Diagnosis Project for Inflammatory Myopathies” revealed that of 460 patients with idiopathic inflammatory myopathies, 51 (11%; female:male, 31:20) had antisynthetase myopathy. It is noted that anti-OJ antibodies, one of anti-ARS antibody subtypes, are clearly detected by RNA immunoprecipitation, but not conventional detection methods including line blot and enzyme-linked immunosorbent assays. The combined mean onset age of the patients was 60 years (range 13–85 years). There were no significant HLA-DRB1 alleles associated with anti-ARS antibodies. All patients with antisynthetase myopathy patients presented muscle limb weakness; 14 had severe weakness, 17 neck weakness, 15 dysphagia, and 15 muscle atrophy. Although patients with anti-OJ antibodies showed severe muscle weakness, the clinical presentations defined by anti-ARS antibodies were relatively homogeneous. In muscle pathology, perifascicular necrosis is a distinctive hallmark of antisynthetase myopathy. Patients with antisynthetase myopathy responded to the combination of immunosuppressive therapy, with favorable outcomes. However, interstitial lung disease, found in 41 patients, was more closely related to mortality than myositis. Antisynthetase myopathy has a distinct clinical and histological entity among idiopathic inflammatory myopathies.
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