Koton S, Pike JR, Johansen M, Knopman DS, Lakshminarayan K, Mosley T, Patole S, Rosamond WD, Schneider AL, Sharrett AR, Wruck L, Coresh J, Gottesman RF. Association of Ischemic Stroke Incidence, Severity, and Recurrence With Dementia in the Atherosclerosis Risk in Communities Cohort Study. JAMA Neurol. 2022 Mar 1;79(3):271-280. PubMed.

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  1. This paper examines the risk of dementia from strokes in the large epidemiologic ARIC study of ~15,000 individuals. It is generally appreciated that stroke and degenerative dementia can provide additive injury to the brain. This paper purports to show increased risk of dementia after stroke(s) “independent of risk factors,” but it does not address the nature of this additivity.

    Particular limitations of this study are: (a) the diagnosis of dementia was made by various fashions, including by telephone interviews and chart and billing code reviews, and there are no biomarkers; (b) the timing of the dementia state is often unclear—i.e., there may have been MCI or mild dementia before stroke, and development of more frank dementia, unsurprisingly, after stroke; (c) the stroke and non-stroke populations differed markedly in a number of ways, including gender, ethnicity, education, tobacco use, BMI, hypertension, diabetes, and hyperlipidemia.

    As in any epidemiologic study, the question is whether the statistical adjustment for these marked confounds is enough to be able to conclude that the dementia was independent of underlying variables that might predispose to both stroke and dementia (including unmentioned variables such as diet, drug use, alcohol use, occupation, or genetics). The demonstration of graded responses of stroke numbers or stroke severity to “risk of dementia” does not obviate the reasonable hypothesis that it is not the “stroke(s)” but rather the underlying status in these individuals that is responsible for the apparent dementia risk.

    No data is provided on the characteristics of the persons with dementia without stroke vs. dementia with stroke (e.g., APOE, test scores, method of dementia diagnosis). The data of this paper contribute to the large body of evidence that having strokes is unfavorable to brain function. And in a similar vein, while all would agree that stroke prevention is a worthy aim, this association data, at its best, does not allow the conclusion that preventing strokes, per se, would affect incidence of dementia.

    View all comments by Lawrence Honig

  2. The main takeaway message of Dr. Koton’s rigorous study is that stroke doubles your risk of dementia. The findings suggest that preventing stroke by controlling vascular risk factors, such as high blood pressure, and maintaining healthy lifestyles is a potential strategy for reducing dementia risk. The results also suggest that clinicians should monitor stroke survivors closely for cognitive decline and dementia over the years after the stroke event.

    One surprise of the study is that vascular risk factors before and after stroke did not explain the risk of post-stroke dementia. One hypothesis is that shared risk factors between stroke and dementia contribute to post-stroke dementia. Another surprise is that black adults had a higher risk of dementia after moderate to severe stroke than did white adults. Black adults have a higher stroke risk than white adults. So, we need to understand better why a stroke is a more potent cause of dementia in black adults.

    Many previous studies of post-stroke dementia risk had mostly white populations and did not control for pre-stroke cognition. Dr. Koton's study findings are robust and generalizable because the study included black and white adults and accounted for pre-stroke cognition.

    View all comments by Deborah Levine

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  1. Stroke Severity, Recurrence Increase Dementia Risk