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Q In older people, does having a stroke increase the risk of developing dementia?
nested case-control study of patients who had a stroke and 5 randomly allocated age and sex matched controls followed up for ⩽10 years. Patients and controls were identified from a stroke free and dementia free inception cohort drawn from the Framingham Study and regularly examined over a 20 year period (1982–2002).
town of Framingham in Massachusetts, USA.
212 patients (mean age 79 y, 61% women) who had their first stroke at <95 years of age, were free from dementia at the time, survived the stroke, and were available for evaluation 6 months after the index stroke. The controls were required to be alive, free from stroke and dementia, and have ⩾6 months of follow up subsequent to the date of stroke in their assigned patient.
stroke was defined as a focal neurological deficit of acute onset, persisting for >24 hours. Cardiovascular risk factors (data collected biennially) included hypertension, diabetes mellitus, atrial fibrillation, cigarette smoking status, and apolipoprotein E genotype. Association between incident stroke and development of dementia was assessed using a Cox proportional hazards model with adjustment for patient demographics and cardiovascular risk factors.
incidence of dementia in patients who scored below an education adjusted cut off of the Mini-Mental Status Examination or who had a decrease in score of ⩾3 points. Patients were initially assessed by a neurologist and a neuropsychologist. Diagnosis of dementia was done by a review panel using Framingham criteria, which conform to Diagnostic and Statistical Manual of Mental Disorders IV criteria.
The 10 year incidence of dementia was greater among patients who had had a stroke than among matched controls (19% v 11%, p<0.001). Overall, the presence of baseline stroke doubled the risk of dementia after adjustment for age, sex, and educational status (table⇓). Additional adjustment for apolipoprotein E genotype status, stroke location, stroke type, presence of a second stroke, and individual stroke risk factors did not substantially alter the risk (table⇓).
In older people, having a stroke increased the risk of developing dementia.
Although previous studies have examined the risk of developing dementia after stroke, the study by Ivan et al is unique in its use of a community based inception cohort free of dementia or stroke. Biennial assessment of the cohort is also a notable strength. The study design minimised the possibility of including individuals with dementia before their index stroke, and the use of a community based cohort ensured the inclusion of patients whose stroke care did not include a hospital stay. Overall the findings are more optimistic than those of previous studies, but they do confirm that stroke is a significant risk factor for developing dementia.
A previous study indicated a 9 fold increase in the risk of developing dementia in the year after stroke,1 but the findings of Ivan et al indicate that the risk of early dementia is not as great as was previously thought. The difference in the findings of Ivan et al and those of earlier studies could be accounted for by the exclusion of patients with pre-existing dementia (before stroke) and the stricter criteria for diagnosing dementia.
The findings of Ivan et al are relevant to nurses working with older people in settings ranging from primary care to acute care. They reinforce the importance of stroke prevention measures, not only in reducing the deleterious effects of stroke itself but also in decreasing the incidence of dementia. The 19% incidence of dementia within 10 years of the index stroke also reinforces the value of regular long term screening after stroke to detect signs of dementia onset and initiate timely, interventions when necessary. Furthermore, clients who are already aware of the increased risk of dementia will probably find it reassuring to know that most people who have a stroke remain dementia free at 10 years.
For correspondence: Dr P A Wolf, Boston University School of Medicine, Boston, MA, USA.
Sources of funding: National Institutes of Health; National Institute of Ageing; National Institute of Neurological Disorders and Stroke; and Boston University Alzheimer’s Disease Center.