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

BACKGROUND: 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. OBJECTIVE: 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. METHODS: 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. RESULTS: 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. DISCUSSION: 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.

Muscle diffusion tensor imaging in glycogen storage disease V (McArdle disease).

PURPOSE: To evaluate differences in diffusion parameters in thigh muscles in patients with glycogen storage disease type V (McArdle disease) using muscle diffusion tensor imaging (mDTI) compared to healthy controls METHODS: In this prospective study, we evaluated thigh muscles from hip to knee of 10 McArdle patients (5 female, mean age 33.7 ± 14.4 years) and 10 healthy age- and gender-matched volunteers. MRI scans were performed at 3 T and comprised mDTI, T1-weighted and T2-weighted imaging between May 2015 and May 2017. Needle biopsy of the vastus lateralis muscle was performed in three McArdle patients. The muscle tissue was analyzed by using histochemical and enzyme-histochemical techniques for glycogen content and histopathological changes. Mean values of the eigenvalues (λ1-λ3), fractional anisotropy (FA), and mean diffusivity (MD) were obtained for the vastus lateralis, vastus medialis, rectus femoris, biceps femoris, semitendinosus, and semimembranosus and compared between groups using Student's t tests, as well as ANCOVA; significance level was set at p < 0.05. RESULTS: Needle biopsy showed intracellular glycogen accumulation in skeletal muscle fibers of three McArdle patients. Extracellular histopathological changes were not found. Muscle DTI analysis did not show statistically significant differences between patients and controls for any of the muscles. CONCLUSION: Despite intracellular glycogen accumulation in the three biopsy samples, mDTI parameters were not altered in McArdle patients compared to controls. We conclude that the currently used mDTI acquisition and processing lack the sensitivity to detect intracellular changes due to accumulated glycogen in this cohort of McArdle patients. KEY POINTS: • Despite intracellular glycogen accumulation in three examined biopsy samples, mDTI parameters were not altered in McArdle patients compared to controls. • In its current form, diffusion MR does not provide additional information in quantifying intracellular glycogen accumulations within skeletal muscle fibers in McArdle patients.