Diffusion Tensor Imaging Shows Differences Between Myotonic Dystrophy Type 1 and Type 2

Myotonic Dystrophies type 1 and type 2 are hereditary myopathies with dystrophic muscle degeneration in varying degrees. Differences in muscle diffusion between both diseases have not been evaluated yet.

To evaluate the ability of muscle diffusion tensor imaging (mDTI) and Dixon fat-quantification to distinguish between Myotonic Dystrophy (DM) type 1 and type 2 and if both diseases show distinct muscle involvement patterns.

We evaluated 6 thigh and 7 calf muscles (both legs) of 10 DM 1, 13 DM 2 and 28 healthy controls (HC) with diffusion tensor imaging, T1w and mDixonquant sequences in a 3T MRI scanner. The quantitative mDTI-values axial diffusivity (λ1), mean diffusivity (MD), radial diffusivity (RD) and fractional anisotropy (FA) as well as fat-fraction were analysed. CTG-triplet repeat-length of DM 1 patients was correlated with diffusion metrics and fat-fraction.

mDTI showed significant differences between DM 1 and DM 2 vs. healthy controls in diffusion parameters of the thigh (all p < 0.001) except for FA (p = 0.0521 / 0.8337). In calf muscles mDTI showed significant differences between DM 1 and DM 2 patients (all p < 0.0001) as well as between DM 1 patients and controls (all p = 0.0001). Thigh muscles had a significant higher fat-fraction in both groups vs. controls (p < 0.05). There was no correlation of CTG triplet length with mDTI values and fat-fraction.

mDTI reveals specific changes of the diffusion parameters and fat-fraction in muscles of DM 1 and DM 2 patients. Thus, the quantitative MRI methods presented in this study provide a powerful tool in differential diagnosis and follow-up of DM 1 and DM 2, however, the data must be validated in larger studies.