Abstract
Background Structural integrity of the ipsilesional corticospinal tract (CST) is important for upper limb motor recovery after stroke. However, additional neuromechanisms associated with motor function poststroke are less well understood, especially regarding the lower limb. Objective To investigate the neural basis of upper/lower limb motor deficits poststroke by correlating measures of motor function with diffusion tensor imaging-derived indices of white matter integrity (fractional anisotropy (FA), mean diffusivity (MD)) in primary and secondary motor tracts/structures. Methods Forty-three individuals with chronic stroke (time poststroke, 64.4 ± 58.8 months) underwent a comprehensive motor assessment and MRI scanning. Correlation and multiple regression analyses were performed to examine relationships between FA/MD in a priori motor tracts/structures and motor function. Results FA in the ipsilesional CST and red nucleus (RN) was positively correlated with motor function of both the affected upper and lower limb (r = 0.36‐0.55, p ≤ 0.01), while only ipsilesional RN FA was associated with gait speed (r = 0.50). Ipsilesional CST FA explained 37.3% of the variance in grip strength (p < 0.001) and 31.5% of the variance in Arm Motricity Index (p = 0.004). Measures of MD were not predictors of motor performance. Conclusions Microstructural integrity of the ipsilesional CST is associated with both upper and lower limb motor function poststroke, but appears less important for gait speed. Integrity of the ipsilesional RN was also associated with motor performance, suggesting increased contributions from secondary motor areas may play a role in supporting chronic motor function and could become a target for interventions.
Highlights
Motor weakness is one of the most disabling consequences of stroke, often leading to difficulties in activities of daily living, gait, and decreased activity levels [1]
Our results show that variability in upper and lower limb motor function in chronic stroke is associated with variability in ipsilesional red nucleus (RN) fractional anisotropy (FA), we cannot directly infer a compensatory role of the rubrospinal tract (RST) in motor recovery
Our findings demonstrate that microstructural integrity of the ipsilesional corticospinal tract (CST) is correlated with both affected upper and lower limb motor function across different ICF domains in chronic stroke
Summary
Motor weakness is one of the most disabling consequences of stroke, often leading to difficulties in activities of daily living, gait, and decreased activity levels [1]. Loss of microstructural integrity of white matter tracts (e.g., local tissue damage within the primary lesion, anterograde, and/or retrograde axonal degeneration) is typically reflected by an increase in MD (representing increased water diffusion in the extracellular space) and/or a reduction in FA (representing decreased anisotropic diffusion) [5] Axonal properties such as density, myelination, diameter, and orientation contribute to overall FA values [6]. To investigate the neural basis of upper/lower limb motor deficits poststroke by correlating measures of motor function with diffusion tensor imaging-derived indices of white matter integrity (fractional anisotropy (FA), mean diffusivity (MD)) in primary and secondary motor tracts/structures. Microstructural integrity of the ipsilesional CST is associated with both upper and lower limb motor function poststroke, but appears less important for gait speed. Integrity of the ipsilesional RN was associated with motor performance, suggesting increased contributions from secondary motor areas may play a role in supporting chronic motor function and could become a target for interventions
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