Stroke-related dementia: rates, risk factors and implications for future research.
Stroke is a risk factor for dementia and dementia predisposes to stroke. Dementia prevalence in subjects with stroke is comparable to that seen in stroke-free subjects who are 10 years older. However, until recently the prevalence, time course and risk factors for dementia in relation to the occurrence of stroke was unclear owing to conflicting reports from individual studies. Data now available from a meta-analysis of studies of pre- and post-stroke dementia, show that heterogeneity between individual studies is largely explained by study methods and case-mix. Pooled dementia estimates are consistent with 1-in-10 patients being demented prior to first stroke, 1-in-10 developing new dementia soon after first stroke, and over 1-in-3 being demented after a recurrent stroke. After the first year, cumulative incidence of dementia is little greater than expected on the basis of recurrent stroke alone. Medial temporal lobe atrophy, female sex and family history, are more strongly associated with pre-stroke dementia, whereas the characteristics and complications of the stroke and the presence of multiple lesions in time and place are more strongly associated with post-stroke dementia, indicating the likely impact of optimal acute stroke care and secondary prevention in reducing the burden of dementia. Future studies are needed to develop a predictive risk score for post-stroke dementia, to evaluate short cognitive screening instruments to identify high risk patients with milder cognitive impairment, and to clarify the interaction between degenerative and vascular processes in the development of dementia.