Magnetic resonance imaging of muscles in myotonic dystrophy

The MR findings in 27 patients with myotonic dystrophy were compared with those observed in 11 patients with other muscular dystrophies: six with limb-girdle dystrophy, three with facioscapulohumeral muscular dystrophy and two with Becker-type muscular dystrophy. Clinical status was graded into 10 stages. The MR study was performed at the medium third of the thigh, with a slice thickness of 7.5 mm (TR: 750/TE: 25 for T1; TR: 2200/TE: 30/90 for DP/T2). Muscle signal intensity was evaluated with a four-point grading scale using subcutaneous fat as a reference. Statistical analysis was done using the Mann-Whitney-Wilcoxon's test and simple linear regression. In the myotonic dystrophy group, 81.4% of the patients showed an abnormal signal at the crural muscle level, adopting a semilunar shape around the anteroexternal side of the femur. The presence and intensity of this hyperintense signal correlated positively with the duration of disease (r = 0.54) and the clinical stage (r = 0.69). Of the 11 patients with other muscular dystrophies, only three (27.2%) showed hyperintense signal at the crural muscle level. MR imaging of patients with muscle disease may contribute to the in vivo study of muscular dystrophy, its differential diagnosis and the detection of asymptomatic patients.