Magnetic resonance imaging of the idiopathic inflammatory myopathies: structural and clinical aspects.

Idiopathic inflammatory myopathies are chronic diseases clinically characterized by symmetrical proximal muscle weakness. MRI has assumed a major role in the evaluation and management of these conditions. It is sensitive to the presence of inflammation and edema, especially with incorporation of fat suppression sequences, so it is a useful tool for establishing an early diagnosis, for evaluating the extent and number of lesions, and for determining the right site for biopsy. The noninvasive nature of the procedure makes it ideal for serial studies to evaluate response to treatment. Whole-body MRI can scan a large volume of muscles without prolonged acquisition time and has the potential to identify previously unsuspected sites of involvement. MRI is also an excellent technique for identifying areas of fatty infiltration within the muscles, which usually occurs in the late stages of inflammatory myopathies. In summary, MRI has revolutionized the way muscular diseases are diagnosed and treated.