Idiopathic inflammatory myositis.

Knowledge on idiopathic inflammatory myopathy (IIM) has evolved with the identification of myositis-associated and myositis-specific antibodies, development of histopathological classification and the recognition of how these correlate with clinical phenotype and response to therapy. In this paper, we outline key advances in diagnosis and histopathology, including the more recent identification of antibodies associated with immune-mediated necrotising myopathy (IMNM) and inclusion body myositis (IBM). Ongoing longitudinal observational cohorts allow further classification of these patients with IIM, their predicted clinical course and response to specific therapies. Registries have been developed worldwide for this purpose. A challenging aspect in IIM, a multisystem disease with multiple clinical subtypes, has been defining disease status and clinically relevant improvement. Tools for assessing activity and damage are now recognised to be important in determining disease activity and guiding therapeutic decision-making. The International Myositis Assessment and Clinical Studies (IMACS) group has developed such tools for use in research and clinical settings. There is limited evidence for specific treatment strategies in IIM. With significant development in the understanding of IIM and improved classification, longitudinal observational cohorts and trials using validated outcome measures are necessary, to provide important information for evidence-based care in the clinical setting.