Magnetic resonance imaging of skeletal muscles in the polymyositis.

Magnetic resonance imaging of skeletal muscles was performed in 11 patients with polymyositis. Two types of muscle lesions were revealed. The first, inflammation, showed increased signal intensity on T2-weighted images and iso-intensity on T1-weighted images. The second, fatty replacement, showed increased signal intensity on both images. The coronal sections could elucidate the extension of the lesion in each affected muscle. Inflammation was relatively diffuse, while homogeneous fatty replacement tended to begin at the lower myotendinous junctions.