Background: Little is known about the association between poststroke cognitive impairment (PSCI) and functional outcome in the acute care phase of ischemic stroke and the influence of the clinical condition of acute stroke on this association. We examined this issue, taking into account stroke-related factors, in a hospital-based prospective study of patients with acute ischemic stroke. The same analysis was also performed after subsequent rehabilitation to investigate whether the association observed in the acute care phase persisted after that. For comparison, the same analysis was performed for pre-stroke dementia (PreSD). Methods: We included in the study a total of 923 patients with acute ischemic stroke who were admitted to a hospital from 2012 to 2020 in Japan. Cognitive function was assessed using the Mini-Mental State Examination and Raven's Colored Progressive Matrices test at an average of 6.3 days after stroke onset. The subjects were divided into three groups with normal cognition, PSCI, and PreSD. Study outcome was a poor functional outcome, defined as a modified Rankin Scale score of ≥3 at the end of acute care (median 21 days after admission). Among total subjects, 460 were also assessed for poor functional outcome after rehabilitation (median 77 days after admission). A logistic regression model was applied in this study. Results: Patients with PSCI and PreSD had higher median National Institute of Health Stroke Scale scores than those with normal cognition (median [IQR]: 3 [2-6], 4 [2-12], and 2 [1-4], respectively). The age- and sex-adjusted cumulative incidence of poor functional outcome was significantly higher in patients with PSCI and PreSD than in those with normal cognition in the acute care and rehabilitation phases. In the acute care phase, these associations remained significant after adjustment for stroke-related factors and other confounders (multivariable-adjusted odds ratio [95% CI] for PSCI vs. normal cognition: 3.28 [2.07-5.20]; for PreSD: 2.39 [1.40-4.08]). Similar results were observed in the rehabilitation phase (for PSCI: 2.48 [1.31-4.70]; for PreSD: 3.92 [1.94-7.92]). Conclusions: Our findings suggest that PSCI, as well as PreSD, is possibly associated with the development of poor functional outcome in the acute care phase of ischemic stroke, and this association continues thereafter.
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