Diffusion Tensor Imaging of the Corticospinal Tract and Walking Outcomes in Multiple Sclerosis

Background: Diffusion Tensor Imaging (DTI) reflects restrictions to diffusion and quantifies disruptions and damage to white matter along the corticospinal tract. Research has identified a significant relationship between DTI indices in the corticospinal tract and disability status in persons with multiple sclerosis (MS). To date, there is little known about the association between DTI indices of the corticospinal tract with walking and gait outcomes in MS. Such inquiry is essential for examining the integrity of white matter pathways as a possible mechanism of walking changes in MS.  

Objectives: This study examined the associations among DTI indices (fractional anisotropy (FA), radial diffusivity (RD), and axial diffusivity (AD)) of the corticospinal tract with walking and gait outcomes in persons with MS.

Methods: We enrolled 58 persons with MS who underwent 3T brain magnetic resonance imaging (MRI) examination including anatomic and DTI acquisitions. We examined white matter structural integrity in the corticospinal tract in the brain with DTI. Motor pathways were identified using tractography to identify the fiber tracts propagating from motor cortex to the midbrain. FA, RD, and AD values were calculated by averaging the respective FA, RD, and AD value for each voxel on the resulting tracts and weighting this value by the probability of a fiber tract passing through that voxel. Measures of FA, RD, and AD for the fiber pathways were created for each hemisphere of the brain that were then averaged to produce a single value for each index. Participants also completed three walking performance assessments: 6-minute walk (6MW), timed 25-foot walk (T25FW), and gait testing.  We examined associations using partial correlations (pr) analyses, controlling for age and sex.

Results: RD was significantly correlated with 6MW performance (pr=-0.276, p=0.04), T25FW (pr=-0.291, p=0.03), and gait velocity (pr=-0.289, p=0.03). AD was significantly correlated with 6MW performance (pr=-0.333, p=0.01), T25FW (pr=-0.339, p=0.01) and gait velocity (pr=-0.328, p=0.01). FA was not significantly correlated with any of the walking parameters (p>0.05).

Conclusions: We provide novel evidence of possible motor pathway damage involved in walking performance in MS. There may be subtle differences in AD and RD associated with walking outcomes, and these could be assessed in future longitudinal examinations and clinical trials of motor rehabilitation.