Inflammatory Myopathy

Abstract

Inflammatory myopathy (IM) comprises a diverse group of acquired skeletal muscle diseases often occurring in complex clinical settings. Reaching an accurate diagnosis is considered a challenge in clinical practice, often requiring multidisciplinary expertise. The majority of IMs have an autoimmune background and the precise mechanism of the immune response in the different groups has not been fully characterized. Since the 1990s, the classification of IM has been limited by specific pathological variants: polymyositis, dermatomyositis, and inclusion body myositis. Several successful attempts have been made to involve autoantibodies in the diagnostic workup. Therefore, different entities have been developed and enrolled into the IM classification including immune-mediated necrotizing myopathy. To date, there is no widely accepted consensus regarding the classification of IMs. The current classification system and literature reviews are somewhat confusing, as they do not actually assist in the reliable diagnosis. Further advanced studies in this area should be conducted. In this chapter, we propose a comprehensive classification of IMs that incorporates clinical information, morphological features, antibody profiles, and molecular data as well as previous classification systems in the literature. This assemblage focuses on recent advances in myositis that can be used as current guidelines to diagnose patients with IM.