The relationship between brain frailty and balance performance in patients with subacute stroke.

INTRODUCTION: Brain frailty, defined by old vascular lesions, white matter hyperintensities, and brain atrophy, reflects cerebral vulnerability after stroke. Its impact on balance recovery in subacute stroke remains unclear. This study examined whether brain frailty is associated with balance function at discharge and whether it mediates the relationship between age and balance outcomes. METHODS: This retrospective cohort study included patients with subacute stroke admitted between July 2021 and June 2024. Brain frailty was scored from 0 to 3 using magnetic resonance imaging within 24 h of stroke onset. Balance function was assessed using the Berg Balance Scale (BBS) at discharge. The association between brain frailty and balance function was examined using multiple regression, and the mediating effect of brain frailty on the relationship between age and balance function was assessed using mediation analysis. RESULTS: A total of 163 patients were analyzed (median age 75 years). Brain frailty scores were 0 in 25 (15.3%), 1 in 45 (27.6%), 2 in 62 (38.0%), and 3 in 31 (19.0%). Brain frailty scores of 1-3 were associated with BBS scores (score 1: B = -6.86, p = 0.009; score 2: B = -5.78, p = 0.031; score 3: B = -7.25, p = 0.021). Brain frailty significantly mediated the age-BBS association (indirect effect B = -0.12, 95% CI -0.23 to -0.03). CONCLUSION: Brain frailty is common in subacute stroke and independently predicts poorer balance recovery. It also shows indirect-only mediation of age-related decline in balance outcomes, supporting its clinical value in rehabilitation.