[Clinical significance of magnetic resonance imaging of skeletal muscles in idiopathic inflammatory myopathies of adults].

The purpose of this study was to evaluate the clinical significance of magnetic resonance imaging (MRI) of skeletal muscles in Japanese patients with idiopathic inflammatory myopathies (IIM). MRI was performed in 23 adult patients with IIM, including 10 with polymyositis, 12 with dermatomyositis, and 1 with focal myositis. Seven (73%) of 11 patients with active IIM and 2 (17%) of 12 patients with inactive IIM showed hyperintensity of T 2-weighted images and normal intensity of T 1-weighted images, indicating "edema-like abnormalities" (MRI findings for active myositis). Muscle lipomatosis and fibrosis were demonstrated in four patients and 1 patient, respectively. Considerable selectivity of muscles in developing inflammatory disorders was found. In quadriceps muscles, for example, vastus muscles seemed to be more often affected in DM patients, whereas adductors were more often affected in PM patients. Serial examination of muscle MRIs was carried out in 4 patients and the findings paralleled the disease activities. The muscle MRI findings did not necessarily correlate with other findings, such as the presence of muscle weakness, elevated serum creatine kinase levels, myogenic electromyogram, or muscle biopsy findings. The muscle MRI was considered to be an additional useful tool for the diagnosis, evaluation of disease activity, and planning treatment of IIM.