Prediction of Stroke Outcomes in a Super-aged Society: Different Effects Among Predictive Variables

Background and objective: Population aging has progressed rapidly worldwide, particularly in developed countries such as Japan. Age is a well-established prognostic factor after stroke; however, its influence on functional outcomes may differ in increasingly older populations. This study aims to investigate whether the impact of age on post-stroke functional independence differs between patients aged ≥75 years (late elderly) and those aged <75 years. Methods: This retrospective cohort study included 169 post-stroke patients admitted to a convalescent rehabilitation ward between 2018 and 2023. All patients were independent before stroke onset and received intensive multidisciplinary rehabilitation. Functional outcomes were assessed using the Functional Independence Measure (FIM), with the motor score at discharge as the primary endpoint. Patients were divided into a younger group referred to as the 'early elderly' (<75 years, n = 80) and an older group known as the 'late elderly' (≥75 years, n = 89). Multivariable linear regression analyses were performed for the entire cohort and separately for each age group, adjusting for demographic, clinical, and functional variables at admission. Results: Baseline FIM motor and cognitive scores and trunk function were significantly poorer in the late elderly group; however, no significant age-related difference in FIM gain was observed. In the overall cohort, age, time from stroke onset to transfer, FIM cognitive score at admission, and trunk function independently predicted the FIM motor score at discharge. In subgroup analyses, age was not a significant predictor in the early elderly group but was a strong independent predictor in the late elderly group, along with cognitive function, motor impairment, trunk function, and time to rehabilitation. Conclusions: The prognostic significance of age differs by age group in post-stroke rehabilitation. Age does not independently predict functional independence in patients aged <75 years, but plays a critical role among those aged ≥75 years. These findings highlight the need for age-specific prognostic models and rehabilitation planning in aging societies, particularly among patients undergoing intensive convalescent rehabilitation.