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Incidence of Poststroke Dementia Remains Highly Prevalent

The risk of dementia was substantial and front-loaded following stroke, with the 1-year prevalence similar to the estimate for dementia at any time point. The findings indicate a need for greater engagement between stroke and dementia care.

A recently conducted systematic review of studies that had ischemic or mixed stroke cohorts found the incidence of dementia to be common following any point after stroke, with more than 1 in 5 people having the disease, some of which predated the stroke.

To understand the epidemiology of poststroke dementia (PSD), senior author Terence J. Quinn, MD, Senior Clinical Lecturer and Honorary Consultant Physician in Stroke, University of Glasgow College of Medical Veterinary and Life Sciences, and colleagues, calculated the pooled prevalence of dementia from 44 extracted studies using random-effects models at any time after stroke—the primary outcome—and at 1 year (range, 6-18 months).

The period of follow-up within the studies ranged from 3 months to 25 years, with 3 months the modal follow-up time point (n = 18). The average age of patients observed was between 56-79.9 years. Among all timeframes, reported prevalence of PSD including prestroke dementia ranged from 8.4%-41.5% across studies, with a pooled prevalence of 22.3% (95% CI, 18.8%-26.2%). Investigators found statistically significant differences for setting (P = .004), stroke type (first vs recurrent; P <.001), year of publication (P = .002) and income (P = .014).

Using available data from 13 hospital-based studies and 3 population-based studies, the estimated prevalence of PSD at 1 year among individuals without prestroke dementia ranged from 1.1% to 39.2%. Ultimately, the pooled prevalence was 18.4% (95% CI, 7.4-38.7), with no statistically significant differences observed within subgroups.

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A total of 4 hospital-based studies and 2 population-based studies had data on the prevalence of PSD including prestroke dementia 1 year after stroke. In total, the estimated prevalence of PSD in the first year ranged from 1.0%-31.0%, corresponding to an estimated pooled prevalence of 20.4% (95% CI, 14.2-28.2). Notably, there was a statistically significant subgroup difference for first vs recurrent stroke type (P <.001).

"Dementia is a progressive condition, yet in our analysis as the length of time between the stroke event and assessment increased, the prevalence of PSD showed a modest decrease. Attrition due to mortality is one plausible explanation," Quinn et al wrote. "In addition, immediately after the stroke event, there are dynamic changes in cognition and attempts at early assessment may overestimate dementia."

When evaluating the PSD prevalence by timeframe since stroke, the pooled prevalence increased from 19.1% at 3 months to 19.8% at 6 months and was then lower for each of the later time points, such as 12-18 months, 2-5 years, and greater than 6 years.

When pooling 19 hospital-based studies and 6 population-based studies, the prevalence for prestroke dementia was 7.6% (95% CI, 4.0-14.0). The Informant Questionnaire on Cognitive Decline in the Elderly questionnaire was used in 13 of the 19 hospital-based studies to obtain rates of prestroke dementia. In contrast, the population-based studies used a variety of methods, including review of medical records and premorbid assessment of cognition.

Quinn and colleagues found no significant relationship between the log event rate for dementia prevalence and year of recruitment of the study for studies excluding prestroke dementia (slope coefficient = 0.03 [standard error (SE), 0.025]; P = .18); however, they did identify a significant relationship between the log event rate in those that did include prestroke dementia (slope coefficient = –0.05 [SE, 0.01]; P = .0000). Notably, no significant association was found between study quality and year of study recruitment (coefficient = –.095; P = .55).

The study authors concluded, "Our findings highlight the need for greater engagement between stroke and dementia care. We would hope that our data on prevalence of PSD highlight the importance of this condition among policy makers, healthcare professionals and the public. Our estimates can be used for planning research, for example, in planning the sample size of a future interventional trial."

Criag L, Hoo ZL, Yan TZ, Wardlaw J, Quinn TJ. Prevalence of dementia in ischemic or mixed stroke populations: a systematic review and meta-analysis. J Neurol Neurosurg Psychiatry. Published online November 15, 2021. Doi:10.1136/jnnp-2020-325796