Background and purpose: Stroke is associated with increased risk of dementia. There has been a decline in mortality from stroke among persons 65 and over in recent decades in the US. It is not clear, however, how this process has affected incidence of various dementias.
Methods: We evaluated over time changes in stroke admission rates and survival, and in rates of newly diagnosed dementias (Alzheimer disease, senile, and cerebrovascular disease-related dementia) in persons with and without stroke aged 65 and over, using Medicare inpatient records, 1984 to 2001, linked to the National Long-Term Care Survey (about 380,000 person-years totally).
Results: Age-adjusted stroke rate increased from 0.0066 to 0.008 (P=0.08) from 1984-1990 to 1991-2001. One-year survival after stroke improved from 53% in 1984 to 1990 to 65% in 1991 to 1996 (P<0.0001). Age-standardized rate of diagnosed dementias increased from 0.0062 in 1984 to 1990 to 0.0095 in 1991 to 2000 (P=0.001). Among stroke patients the rate rose from 0.043 to 0.080. The relative increase in risk was largest for cerebrovascular disease-related dementia (3.68). For senile dementia, the increase was small and not significant. Rates of dementia among persons without stroke rose mainly attributable to Alzheimer disease.
Conclusions: Mortality from stroke declined mainly because of declining stroke case-fatality. In parallel, the rate of diagnosed dementia increased. The increase was larger for persons with stroke compared with stroke-free population. Improved survival from stroke may contribute to this trend. Other contributing factors may include better diagnostics, an increased propensity to make the diagnosis, and increasing dementia risk attributable to factors other than stroke.