MRI of myositis and other urgent muscle-related disorders

Myositis has many etiologies, and it can be encountered in the acute or chronic setting. Our goal is to increase the radiologist's knowledge of myositis and other urgent muscle disorders encountered in the emergent or urgent setting. We review the clinical presentation, the MRI appearance, and the complications that can be associated with these entities. Since myositis can affect multiple muscle compartments, we review how to differentiate the compartments of the appendicular skeletal in order to generate reports that relay important anatomic information to the treating physician. Given the poor sensitivity and positive predictive value of the clinical signs and symptoms used to diagnosing acute compartment syndrome, we discuss the potential use of MRI in cases of suspected but clinically equivocal compartment syndrome in the future.