A longitudinal diffusion tensor imaging study on Wallerian degeneration of corticospinal tract after motor pathway stroke

Wallerian degeneration of the corticospinal tract (CST) after motor pathway ischemic stroke can be characterized by diffusion tensor imaging (DTI). However, the dynamic evolution of the diffusion indices in the degenerated CST has not previously been completely identified. We investigated this dynamic evolution and the relationship between early changes of the diffusion indices in the degenerated CST and long-term clinical outcomes. DTI and neurological examinations were performed repeatedly in 9 patients with first-onset motor pathway subcortical infarction at 5 consecutive time points, i.e. within 1 week, at 2 weeks, 1 month, 3 months and 1 year. Using a region of interest method, we analyzed the ratios of the fractional anisotropy (rFA), mean diffusivity (rMD), primary eigenvalue (rλ1) and transverse eigenvalue (rλ23) between the affected and unaffected sides of the CSTs. We did not find any significant changes in the diffusion indices of the contralesional CSTs across time points. The rFA decreased monotonously during the first 3 months and then stabilized. The rMD increased after 2 weeks and stabilized after the third month. The rλ1 decreased during the first 2 weeks and then remained unchanged. The rλ23 increased during the first 3 months and then stabilized. We also found that the changes in the rFA between the first 2 time points were correlated with the NIHSS (P = 0.00003) and the Motricity Indices (P = 0.0004) after 1 year. Our results suggest that for patients with motor pathway stroke the diffusion indices in the degenerated CST stabilize within 3 months and that early changes in the rFA of the CST may predict long-term clinical outcomes.