Musculoskeletal Ultrasound in Inclusion Body Myositis: A Comparative Study with Magnetic Resonance Imaging.

The objective of this study was to compare the accuracy of ultrasound (US) with that of magnetic resonance imaging (MRI) in identifying muscle abnormalities in patients with inclusion body myositis (IBM). Twelve patients with IBM underwent muscle US and MRI on the same day. Twelve muscle groups were analyzed per patient. On US, a visual grading system was used to detect whether the muscles were affected. On MRI, muscle atrophy, fat infiltration and edema patterns were analyzed. The inter- and intra-reader reproducibility was similar for US and MRI in the evaluation of muscle abnormalities. All patients with muscle abnormalities identified on US presented with fat infiltration on MRI, which was the most common abnormality identified on MRI. Most importantly, the accuracy of US compared with that of MRI for the detection of muscle abnormalities in patients with IBM was 86.8 (κ coefficient = 0.632), with a sensitivity of 84% and specificity of 100%. In conclusion all patients with muscle abnormalities identified on US presented with fat infiltration on MRI, and the marked increase in echo intensity observed in the muscles of IBM patients was related mostly to fatty replacement. Most importantly, US exhibited significant accuracy compared with MRI.