Does the influence of stroke on dementia vary by different levels of prestroke cognitive functioning?: a cohort study.

BACKGROUND AND PURPOSE The association between stroke and subsequent dementia or Alzheimer disease is well established. What is less understood is the extent to which this association is dependent on prestroke cognitive functioning. The study estimated the occurrence in poststroke dementia as a function of prestroke cognitive status and incident stroke. METHODS Study data were derived from the English Longitudinal Study of Ageing, a 10-year long prospective cohort study of older adults living in England. Baseline data (2002/2003) were used to group participants into tertiles of cognitive, memory, and executive functioning before an incident stroke. Data from 4 follow-up surveys were used to identify new stroke and poststroke dementia events. RESULTS The analyses were based on 10 809 participants aged≥50 years at baseline. High prestroke executive functioning was associated with lower relative risk (RR) of dementia (RR, 0.24; 95% confidence interval, 0.13-0.45; P<0.001). Stroke was associated with increased RR of poststroke dementia (RR, 2.63; 95% confidence interval, 1.80-3.84; P<0.001). The association of stroke with poststroke dementia was greater for participants with higher prestroke executive functioning (interaction term RR, 4.4; 95% confidence interval, 1.35-14.63; P=0.014). For participants with higher executive functioning, the probability of dementia was 0.3% without stroke and 3.1% after stroke, compared with 1.9% and 5.2% for lower executive functioning. CONCLUSIONS Stroke and prestroke cognition were independently associated with increased probability of poststroke dementia. Stroke results in disproportionate increase in the risk of dementia when premorbid cognitive functioning is high.