Altered Corticospinal and Intracortical Excitability After Stroke: A Systematic Review With Meta-Analysis

Background Intracortical inhibitory/faciliatory measures are affected after stroke; however, the evidence is conflicting. Objective This meta-analysis aimed to investigate the changes in motor threshold (MT), motor evoked potential (MEP), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF), and identify sources of study variability using a machine learning approach. Methods We identified studies that objectively evaluated corticospinal excitability and intracortical inhibition/facilitation after stroke using transcranial magnetic stimulation. Pooled within- (ie, affected hemisphere [AH] vs unaffected hemisphere [UH]) and between-subjects (ie, AH and UH vs Control) standardized mean differences were computed. Decision trees determined which factors accurately predicted studies that showed alterations in corticospinal excitability and intracortical inhibition/facilitation. Results A total of 35 studies (625 stroke patients and 328 healthy controls) were included. MT was significantly increased and MEP was significantly decreased (ie, reduced excitability) in the AH when compared with the UH and Control (P < .01). SICI was increased (ie, reduced inhibition) for the AH when compared with the UH, and for the AH and UH when compared with Control (P < .001). ICF was significantly increased (ie, increased facilitation) in the AH when compared with UH (P = .016) and decreased in UH when compared with Control (P < 0.001). Decision trees indicated that demographic and methodological factors accurately predicted (73%-86%) studies that showed alterations in corticospinal and intracortical excitability measures. Conclusions The findings indicate that stroke alters corticospinal and intracortical excitability measures. Alterations in SICI and ICF may reflect disinhibition of the motor cortex after stroke, which is contrary to the notion that stroke increases inhibition of the affected side.