Reliability and accuracy of skeletal muscle imaging in limb-girdle muscular dystrophies.

Abstract

To evaluate the reliability and accuracy of skeletal muscle CT to correctly identify different muscular dystrophies manifesting with limb-girdle weakness. Four evaluators assessed scans from 118 patients with limb-girdle muscular dystrophy (LGMD) caused by mutations in 7 different genes and from 32 controls. The conditions studied were scans of genetically confirmed cases of Becker muscular dystrophy (BMD) (n = 28), LGMD2C-F (sarcoglycanopathies) (n = 11), LGMD2I (n = 4), LGMD1B (n = 26), LGMD2A (n = 24), Bethlem myopathy (n = 14), and LGMD2L (n = 11). The control group (n = 32) consisted of patients with neuromuscular disorders manifesting with limb-girdle weakness in which the aforementioned muscular dystrophies were excluded. The scans were compared with the characteristic patterns described in literature. The overall interobserver agreement was poor (κ = 0.27), with markedly higher scores for BMD (κ = 0.51) and Bethlem myopathy (κ = 0.59). The sensitivity to detect selective patterns in relation to the genetic diagnosis was 40% if all LGMDs were taken together. The specificity was 58%, positive predictive value (PPV) 77%, and 1 - negative predictive value (NPV) 79%. Markedly better scores were observed for BMD (sensitivity 91%, PPV 66%, 1 - NPV 3%) and Bethlem myopathy (sensitivity 90%, PPV 69%, 1 - NPV 1%). Our findings suggest that muscle CT might be an adjunct to the clinical diagnosis of BMD and Bethlem myopathy. However, pattern recognition was cumbersome in the other LGMDs.