Examining the relationship between corticospinal tract anatomy, physiology, and upper extremity motor function after acute stroke

Abstract The initial weeks after stroke are critical for upper extremity (UE) motor recovery. It is known that the integrity of the corticospinal tract (CST) plays an important role in UE motor function and recovery. However, the relationships between CST anatomy, physiology, and UE motor function are not well understood. Therefore, this study aims to investigate the relationship between assessments of CST anatomy via magnetic resonance imaging (MRI), CST physiology via transcranial magnetic stimulation (TMS), and UE motor function during early stroke recovery. Our hypothesis was that due to broad network effects after acute stroke such as diaschisis, physiologic measures of CST would be more strongly related to UE motor function than anatomic measures. Thirteen adults (65.44 ± 12.52 years) with first-ever stroke resulting in UE weakness were eligible for and included in this study. Motor assessments including the Fugl-Meyer Assessment-Upper Extremity (FMA-UE), Box and Block Assessment (BB), Grip strength, and SAFE Score were performed. TMS was performed within 5.2 ± 2.2 days post-stroke. MRI was obtained as part of the standard-of-care acute stroke workup, from which CST injury was derived. Resting motor threshold (RMT) and CST injury demonstrated a weak positive relationship (rho=0.37, p>0.05). RMT showed strong, significant negative associations with all UE motor behavioral outcomes (FMA-UE: rho=-0.71, p<0.01; BB: rho=-0.78, p<0.01; Grip Strength: rho=-0.72, p<0.01; SAFE Score: rho=-0.78, p<0.01) while CST injury showed weak to moderate negative associations with the UE behavioral outcomes (FMA-UE: rho=-0.35; BB: rho=-0.32; Grip Strength: rho=-0.26; SAFE Score: rho=-0.26; all p>0.05). These results suggest that TMS- and imaging- based assessments have different relationships to UE motor function during the acute stroke recovery period. TMS neurophysiologic measures are more strongly associated with initial UE deficits than imaging measures, suggesting that TMS measures may capture the influence of network-level processes, such as diaschisis, on UE motor function. Research Category and Technology and Methods Clinical Research: 10. Transcranial Magnetic Stimulation (TMS) Keywords: Upper Extremity Motor Function, Transcranial Magnetic Stimulation, Magnetic Resonance Imaging, Stroke