Association between aphasia and risk of dementia after stroke

Background and purpose: Although findings from published studies suggest post-stroke aphasia is associated with an increased risk of dementia, few studies have evaluated its association in a nationally representative cohort with long-term follow-up. No studies have reported data by type of stroke. Therefore, we examined the association between post-stroke aphasia and the risk of developing dementia. Methods: Using claims data from Taiwan's universal health insurance program, a cohort of patients ≥18 years old with an initial hospitalization for stroke in 2002–2005 were identified and followed up until December 31, 2016. Patients with newly diagnosed aphasia during stroke hospitalization or within 6 months of discharge were defined as the aphasia group. Cox proportional hazards models were used to estimate hazard ratios (HRs) for developing overall, vascular, and non-vascular dementia in patients with and without post-stroke aphasia. Results: During a median follow-up period of 7.9 and 8.6 years for the aphasia (n=17063) and non-aphasia groups (n=105940), respectively, overall dementia incidence was similar, whereas vascular dementia incidence was higher in the aphasia group (7.52 vs. 5.52 per 1000 person-years). The adjusted HRs (95% confidence intervals) were 1.11 (1.06–1.17), 1.42 (1.31–1.53), and 0.94 (0.88–1.01) for overall, vascular, and non-vascular dementia, respectively. The association between aphasia and the risk of vascular dementia did not differ by stroke type (P for interaction=0.43). The analysis of 16856 propensity score-matched pairs revealed similar results. Conclusion: Patients with post-stroke aphasia have an increased risk of developing vascular dementia irrespective of the type of stroke.