157 - Etiology and pathogenesis of inflammatory muscle disease (myositis)

Abstract

The idiopathic inflammatory myopathies (IIMs) encompass a group of heterogeneous disorders that share the clinical features of slowly progressive weakness of skeletal muscle, decreased muscle endurance, muscle fatigue, and inflammation in skeletal muscle tissue. Other organs are frequently affected by inflammation such as skin, joints, lungs, gastrointestinal tract, and occasionally the heart, suggesting that the IIMs are systemic inflammatory disorders. Autoantibodies are frequently found in patients with IIMs, emphasizing the autoimmune pathophysiology of these disorders, but the target autoantigens still need to be defined. Both genetic and environmental factors contribute to susceptibility, and with the heterogenic spectrum of disease it is likely that varying factors are important in different subsets of disease. Muscle weakness is the major clinical feature shared by most patients with IIM, but the molecular mechanisms that lead to muscle weakness and low muscle endurance have still not been clarified in detail. It is clear, however, that different mechanisms, both immune and nonimmune, contribute as supported by the observation that both immune suppression and exercise is required to recover muscle performance. The myositis-specific autoantibodies that are associated with different clinical phenotypes suggest that different molecular pathophysiology may predominate in different subsets of IIM, and for future research subdividing patients into homogenous subgroups will be important to improve our understanding of pathophysiology of IIM. One such way to subgroup patients will be through autoantibody profile.