Imaging of skeletal muscle

Imaging techniques play a key role in the assessment of patients with the idiopathic inflammatory myopathies (IIM). Magnetic resonance imaging (MRI) can reveal muscle inflammation similarly to muscle scintigraphy and 18F-Fluorodeoxyglucose positron emission tomography, but is also able to visualize findings of chronic muscle damage such as muscle atrophy or fat replacement. Ultrasonography has a more limited role because it can only depict the superficial muscle layers. Imaging findings are not specific to IIM, but in the appropriate clinical context they support the diagnosis. MRI is also useful to target biopsy to affected muscles, thus increasing biopsy yield. In addition, because different myopathies present with different patterns of muscle involvement, imaging studies can provide differential diagnostic clues. Finally, imaging studies—especially MRI—can be used to monitor the effects of treatment by serially evaluating changes in muscle inflammation and damage.