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.