Abstract TMP34: Lower Limb Motor Performance is Proportional to Corticospinal Tract Integrity in Chronic Stroke

Abstract

Introduction: Gait is a complex behavior characterized by an array of measures, each contributing to our understanding of gait performance. To improve gait recovery after stroke, we need to connect complex clinical function and brain structure. Here, our purpose is to evaluate the relationship between lower limb performance and structural integrity of corticospinal tract (CST) in ambulatory chronic stroke survivors. Methods: Diffusion weighted images (DWIs) and lower limb performance measures were acquired from 36 chronic (>6 months) stroke survivors with lower limb deficits. Clinical measures included Fugl-Meyer(FM), Gait Assessment and Intervention Tool (GAIT), timed-up-and-go (TUG) and fastest gait speed (GS). Lesions were manually outlined on the MRIs, and left hemisphere lesions were flipped. DWIs were preprocessed using standard denoising techniques before calculating fractional anisotropy (FA), mean diffusivity (MD) and radial diffusivity (RD). Tract-based spatial statistics (TBSS) was used to normalize all data to MNI space and project it onto a skeleton of white matter tracts. CSTs were isolated. Voxel-wise analysis was performed with permutation testing (5000 permutations). A regression model was created for each clinical variable using lesion masks as a regressor. Results: Participants were 64±8.9 y/o, 83% male and 53% left hemisphere lesion. FM was 24.1±4.1. Mild correlations were present for FM with GAIT (Pearson, r = -0.33, p = 0.045) and GS (r = 0.34, p = 0.038), and GS with GAIT (r = -0.35, p = 0.036). TUG was highly correlated with GS (r = -0.93, p = 0.000). In exploratory analysis, findings for ipsilesional CST were as follows: 1) better FM was associated with higher FA, MD and RD, p = 0.001, 0.002 and 0.006 respectively; 2) better GS with higher FA, p = 0.034,3) better TUG scores with lower RD, p = 0.041 and 4) a trend of GAIT with RD, p=0.054. Location of statistically significant voxels varied for different clinical measures. No associations were found for contralesional CST. Conclusion: Structural correlates of lower limb performance can be detected using diffusion weighted tractography. FM, an impairment measure of paretic limb, has a stronger association with CST integrity than the measures of global gait function (TUG and GS).