Making the Diagnosis of Myositis: Muscle MRI

The term “idiopathic inflammatory myopathies” (IIM) or myositis comprises a group of diverse and rare multisystem diseases that present with skeletal muscle weakness due to various degrees of muscle inflammation. Muscle imaging offers a noninvasive and sensitive overview of the regional pattern of muscle involvement and the possibility to guide muscle biopsy as the gold standard for IIM diagnosis. Muscle MRI may also assist in the differential diagnosis of IIM mimics. At follow-up, muscle MRI may be used to monitor treatment response, especially when compared to the baseline MRI, and to differentiate IIM activity from damage. This chapter provides an overview of muscle MRI and other imaging tools that may have future application in IIM.