Edema seen on MRI correlates with inflammation, and biopsy yield can be enhanced by targeting the muscle with the greatest amount of edema and the least fatty tissue replacement. ![]() Suitable targets for muscle biopsy can sometimes be more easily identified with MRI, especially for inflammatory myopathies with patchy distribution of inflammation that results in high rates of sampling error and nondiagnostic biopsies. In the few studies evaluating the diagnostic accuracy of muscle imaging, it has been shown to help identify the molecular basis of myofibrillar myopathies, 1 muscular dystrophies with rigid spine, 2 and distal myopathies, 3 but the ability to distinguish between most limb-girdle muscular dystrophies (LGMD) on imaging was poor. In this regard, certain imaging patterns are more specific and informative than others. An adjunctive role for MRI remains for example, there are distinctive imaging findings that can support the pathogenicity of a variant of uncertain significance (VUS) or direct attention to a gene that may have been overlooked. This approach, however, has been largely superseded by the advent of next-generation gene panels and whole-exome sequencing. Diagnostic algorithms incorporating imaging and clinical findings, have been proposed to direct genetic testing. In practice, muscle MRI is most commonly used diagnostically, especially for inherited myopathies. We review the clinical use of muscle MRI with an emphasis on the basic aspects of muscle MRI interpretation and different patterns of muscle involvement in various myopathies. Muscle MRI can also be helpful in selecting a muscle for biopsy and there is growing interest in using muscle MRI to assess response to treatment in clinical trials and practice. Distinctive MRI findings are also seen in some inflammatory myopathies and spinal muscular atrophy (SMA). ![]() Certain patterns are specific for a particular myopathy and others are common to multiple disorders. These patterns are established by the identification of preferentially involved and preferentially spared muscles, which may not always be clinically observable. Most commonly it is used for diagnosis of inherited myopathies that have distinctive patterns of muscle involvement on MRI. Muscle MRI allows the identification of edema and fatty replacement of muscle tissue. Muscle MRI can provide information that is complementary to clinical, histologic, genetic, and laboratory findings for the diagnosis of neuromuscular disease.
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