Muscle Diffusion Tensor Imaginig in Facioscapulohumeral muscular dystrophy

Introduction/Aims

Muscle diffusion tensor imaging (mDTI) has not yet been explored in facioscapulohumeral muscular dystrophy (FSHD). We aimed to assess diffusivity parameters in FSHD subjects compared to healthy controls (HCs), with regard to their ability to precede any fat replacement process in the muscle.

Methods

Fat Fraction (FF), water T2 (wT2), Mean, Radial and Axial Diffusivity (MD, RD, AD)  and Fractional Anisotropy (FA) of thigh muscles were calculated in a cohort of ten FSHD subjects and fifteen age-matched HCs. All parameters were compared between FSHD subjects and controls, exploring also their values along the main axis of the muscle. Diffusivity parameters were tested as predictors of disease involvement in muscle compartments with no significant fat substitution and edema. Whole-thigh mDTI values were correlated to clinical severity scores.

Results

FF and wT2 were significantly higher in FSHD than controls whereas MD, RD and AD were significantly lower than controls (p < .05). No difference with controls was shown for FA. FF positively correlated with FA and negatively with MD, RD and AD. FF and FA showed significantly higher values distally than proximally. whereas wT2, MD, RD, AD showed lower values distally than proximally (p<.05). Muscles with no significant fat replacement or edema showed a significantly lower AD and FA than controls. FA was the only parameter to positively correlate with the 6-Minute Walking Test.

Discussion

Our results suggest that mDTI parameters appear to predominantly reflect fat replacement in FSHD and might be able to show disease involvement in muscles even before significant fat replacement.