Idiopathic inflammatory myopathies: a comprehensive review, new concepts on diagnostic imaging and whole-body MRI

Idiopathic inflammatory myopathies (IIM) constitute a heterogeneous group of rare autoimmune, chronic inflammatory muscle disorders, resulting in both musculoskeletal and systemic manifestations. They are the leading cause of potentially treatable myositis in both pediatric and adult populations. Precise diagnosis is imperative, as treatment options differ for each disease, directly influencing the patient's therapeutic response and prognosis. The integration of pathological, clinical, serological, and imaging data is vital because of the nonspecific or nearly normal histopathological findings observed in certain cases. Magnetic resonance imaging (MRI) is the preferred imaging modality for IIM assessment, capable of revealing disease activity and distribution patterns, and assisting in the selection of biopsy sites. Advanced techniques such as diffusion-weighted imaging and whole-body MRI have enhanced MRI performance in evaluating inflammatory activity and disease progression. This review examines the clinical and MRI characteristics of the subtypes of IIM, and addresses other important differentials, namely eosinophilic fasciitis and vasculitis with muscle involvement, emphasizing recent advancements in imaging techniques and the significance of a comprehensive approach in myositis evaluation. KEY POINTS: Question IIM and other myositis pose significant diagnostic challenges due to overlapping characteristics. Can advanced imaging modalities improve diagnostic accuracy, monitoring, and treatment decisions? Findings MRI, with emphasis on whole-body MRI, is highly effective in evaluating myopathies, facilitating disease activity detection, guiding biopsies, and differentiating subtypes through distinct imaging patterns. Clinical relevance Advanced imaging techniques contribute to early and precise diagnosis of IIM, optimize therapeutic strategies, and enhance disease monitoring. Whole-body MRI is instrumental in identifying systemic involvement, enabling timely intervention, and improving patient outcomes.