Muscle magnetic resonance imaging findings in patients with idiopathic inflammatory myopathies

Abstract Background Idiopathic inflammatory myopathies (IIMs) are disorders that cause chronic muscle inflammation and weakness due to an autoimmune pathogenesis. Dermatomyositis (DM) is a typical IIM disorder, along with others including antisynthetic syndrome (ASS), immune‐mediated necrotizing myopathy (IMNM), overlap myositis, inclusion body myositis (IBM), and anti‐mitochondrial M2 antibody‐positive myositis (AMA‐myositis). Noninvasive muscle magnetic resonance imaging (MRI) is useful for determining the distribution, nature, and extent of lesions in affected muscles. T 1 ‐weighted MRI is useful for observing morphological changes, including muscle atrophy. Short tau inversion recovery images or T 2 ‐weighted images are useful for detecting muscle inflammation and edema and are suitable for selecting optimal biopsy sites. Muscle MRI is also useful for follow‐up studies. Results On muscle MRI, patients with DM show a symmetric pattern with prominent fasciitis. The MRI findings in ASS are similar to those in DM. In IMNM, MRI findings are asymmetric, present a rapid and severe course, and fasciitis is less prominent. In IBM, atrophy is more severe at presentation than in other IIMs, and fasciitis is absent. In AMA‐myositis, fasciitis is severe and atrophy is mild. Conclusion Muscle MRI can help differentiate between IIMs along with using other laboratory findings, including myositis‐specific antibodies.