Idiopathic Inflammatory Myopathies: Recent Evidence Linking Pathogenesis and Clinical Features

Idiopathic inflammatory myopathies are rare and complex representatives of systemic connective tissue diseases. Described initially as only two entities, recent advances in molecular and imaging techniques now divide them into many subtypes, each with unique pathogenesis and clinical phenotypes. Dermatomyositis and its juvenile form are the most prevalent subtypes and are characterized by systemic vasculopathy and humoral autoimmunity. Genetic predisposition and environmental triggers initiate immune tolerance breakdown, leading to autoantibody production, complement activation, and tissue damage. Anti-synthetase syndrome primarily affects the lungs, where immune responses to aminoacyl-RNA synthetases drive vasculopathy, lung inflammation, and fibrosis. Immune-mediated necrotizing myopathies are muscle-specific, with autoantibodies inducing fiber necrosis and atrophy. Lastly, sporadic inclusion body myositis is a slowly progressive myopathy in which dysfunctional protein handling and autophagy are more important pathogenic elements than muscle inflammation itself. The expanding body of basic science evidence can be overwhelming, making it challenging to connect pathogenic mechanisms to clinical manifestations. This review aims to address this challenge by presenting recent insights into myositis pathogenesis from a practical perspective, reinforcing the links between basic science and clinical semiology.