Microstructural degeneration underlies executive dysfunction after stroke

ObjectiveExecutive dysfunction affects 40% of stroke patients and is associated with poor quality of life. Stroke severity and lesion volume rarely predict whether a patient will have executive dysfunction. Stroke typically occurs on a background of cerebrovascular burden, which impacts cognition and brain network structural integrity. We investigated whether measures of white matter microstructural integrity and cerebrovascular risk factors better explain executive dysfunction than markers of stroke severity. MethodsWe used structural equation modelling to examine multivariate relationships between cerebrovascular risk, white matter microstructural integrity (fractional anisotropy and mean diffusivity), stroke characteristics and executive dysfunction in 126 stroke patients (mean age 68.4 years), three months post-stroke, and compared to 40 age- and sex-matched control participants. Executive function was measured using the Trail Making Tests, Clock Drawing task and Rey Complex Figure copy task. Microstructural integrity was estimated using a standard pipeline to process diffusion weighted images. ResultsExecutive function was below what would be expected for age and education level in stroke patients (t-test compared to controls t(79)=5.75, p<0.001). A multivariate structural equation model illustrated the complex relationship between executive function, white matter integrity, stroke characteristics and cerebrovascular risk. Pearsons correlations confirmed a stronger relationship between executive dysfunction and white matter integrity, than executive dysfunction and stroke severity. Mediation analysis showed the relationship between executive function and white matter integrity is mediated by cerebrovascular burden. InterpretationWhite matter microstructural degeneration of the superior longitudinal fasciculus in the executive control network better explains executive dysfunction than markers of stroke severity.