Stroke and the risk of Alzheimer disease

Background: Alzheimer disease (AD) and stroke are common in elderly individuals, but the relation between these 2 disorders remains uncertain. Objective: To investigate the association between a clinical history of stroke and subsequent risk of AD. Design: A cohort of 1766 Medicare recipients without dementia participated in a longitudinal follow-up study from 1992 through 1999 in upper Manhattan, New York, NY. History of stroke and presence of cardiovascular risk factors were ascertained at the onset of the study. Incidence rates for AD among those with and without stroke were calculated; proportional hazards ratios were computed using age at onset of the disease as the time-to-event variable. Results: The annual incidence for AD was 5.2% among individuals with stroke vs 4% for those without stroke. The hazards ratio for AD among those with a history of stroke was 1.6 (95% confidence interval, 1.0-2.4) compared with those without stroke. Of the vascular risk factors, hypertension, diabetes, and heart disease, only diabetes related to risk of AD in the absence of stroke. Stroke remained weakly associated with AD in the absence of these factors, but risk significantly increased with the additional factors of hypertension (relative risk, 2.3; 95% confidence interval, 1.4-3.6), diabetes (relative risk, 4.6; 95% confidence interval, 2.2-9.5), or heart disease (relative risk, 2.0; 95% confidence interval, 1.2-3.2). Conclusions: Stroke is associated with AD among elderly individuals. The relation is strongest in the presence of known vascular risk factors. The observed association between stroke and AD might relate to an underlying systemic vascular disease process, or alternatively, to the additive effects of stroke and AD pathologic features, leading to an earlier age at onset of disease.