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. The clinical phenotypes of inflammatory myopathies are characterized by various autoantibodies that are originally detected by RNA or protein immunoprecipitation. However, since the correlation between histological features and autoantibodies had not been fully elucidated, we created the “Integrated Diagnosis Project for Inflammatory Myopathies” in October 2010. Based on our work and previous studies, the three major subsets of inflammatory myopathies defined by autoantibodies are immune-mediated necrotizing myopathy (IMNM), antisynthetase syndrome, and dermatomyositis. IMNM is the pathological entity, characterized by significant necrotic and regeneration muscle fibers with minimal or no inflammatory cell infiltration. The detection of autoantibodies against signal recognition particles or 3-hydroxy-3-methylglutaryl-coenzyme A reductase is important for the diagnosis of IMNM. Antisynthetase syndrome, characterized by myositis, interstitial lung disease, skin rash, arthropathy, and Raynaud phenomenon, is the clinical entity based on the presence of aminoacyl transfer RNA synthetase antibodies. Perifascicular necrosis is a distinctive hallmark of antisynthetase syndrome in muscle pathology. The diagnosis of dermatomyositis is usually based on clinical features of typical skin rash. Several autoantibodies are associated with specific subsets of dermatomyositis. Myxovirus resistance A expression in the myofiber cytoplasm has a better sensitivity for the diagnosis of dermatomyositis compared to perifascicular atrophy. The screening of autoantibodies has clinical relevance for managing patients with inflammatory myopathies.
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