Recovery after spinal cord relapse in multiple sclerosis is predicted by radial diffusivity

Background: The aim of this study was to determine whether the diffusion tensor-derived radial diffusivity and axial diffusivity, measured in the cortico-spinal tract in the cervical cord, predict clinical recovery after a cord relapse in patients with multiple sclerosis, and change over time. Methods: Fourteen patients were clinically assessed at the onset of a cervical cord relapse and after 1, 3 and 6 months. Patients and 13 age-matched healthy controls underwent spinal cord diffusion tensor imaging at each time point. The directional diffusivities from diffusion tensor imaging, termed radial diffusivity and axial diffusivity, were calculated in regions of interest placed in the lateral columns, where the cortico-spinal tract is located, and in the anterior and posterior columns. Regression analyses identified predictors of clinical outcome, adjusting for age, gender, cord cross-sectional area and baseline clinical score, and estimated the differences in the rate of change in diffusion tensor imaging measures between groups over time, adjusting for changes in cord cross-sectional area. Results: Lower radial diffusivity of the cortico-spinal tract at baseline was associated with better clinical outcome. As patients improved clinically during the follow-up, they showed greater decrease in radial diffusivity of the cortico-spinal tract than controls. Conclusions: The predictive role of radial diffusivity and its dynamic changes over time suggest that this index reflects spinal cord pathological processes, including resolution of inflammation and remyelination, that contribute to clinical recovery in multiple sclerosis. This suggests that radial diffusivity may be useful in trials that promote recovery after spinal cord injury and could be applied to other neurological diseases affecting the spinal cord.