March 15, 2000 (Atlanta) -- One of every four stroke survivors develops dementia, according to research reported in the March 14 issue of the journal Neurology. The study is the first to include a large number of non-white people -- and in perhaps its most provocative finding it suggests that the risk of dementia after stroke is up to three times higher for black and Hispanic patients than for white patients.
A stroke is a sudden loss of brain function usually caused by a blocked blood vessel that causes loss of oxygen in a particular part of the brain. There may be sudden loss of vision, strength, balance, coordination, speech, or the ability to understand speech. Symptoms such as vomiting, nausea, hiccups, or difficulty swallowing may occur, and there can be severe headache followed by loss of consciousness.
Dementia is a loss of mental function that may include loss of memory and/or judgement, often with changes in personality.
A person's education also played a major role in determining whether dementia followed stroke, according to the study. Compared to stroke patients with 13 or more years of education, those who had only eight years of schooling had four times the risk of dementia. Those with nine to 12 years of school had three times the risk.
"It's always important to think of the public health implications of studies like this," lead author David W. Desmond, PhD, tells WebMD. "It shows that there are certain groups that are at increased risk, and attention needs to be given to these groups to find out why. Ours is the largest study of stroke and dementia ever published. It is not just large but has a high proportion of black and Hispanic patients, and this allows us to identify the risks that they face."
New studies to investigate the basis for these risks already are being planned, says John R. Marler, MD, associate director for clinical trials at the National Institute for Neurological Disorders and Stroke (NINDS), which funded the current study.
"It's a very complex question that a number of studies have looked at and none of them have sorted it out," Marler tells WebMD. "It seems that a lot of the risk factors for stroke are heightened in nonwhites as well -- hypertension, high cholesterol, smoking -- but these risk factors alone don't entirely explain the risk. Is some component cultural or based on some [physical] difference between groups? We haven't been able to sort that out yet. ... There are all sorts of opinions, but there are no scientific answers right now."
Desmond, assistant professor of pathology and neurology at SUNY Downstate Medical Center in Brooklyn, says that his study may actually have underestimated the number of patients who develop dementia after stroke. One reason is that the study used a conservative definition of dementia. Another reason is that because dementia indicates that the person suffered a more severe stroke, many patients with dementia died before they could be tested.
The study analyzed stroke patients at a community health center in northern Manhattan. It found three types of risk factors for dementia after stroke. The first type depended on the part of the brain affected by the stroke: people who had damage to the left side of the brain, which controls language functions and abstract thinking, were more likely to suffer dementia.
The second type depended on a person's risk factors for severe stroke: patients with diabetes or a prior stroke had increased risk of dementia. The third type of risk depended on patient factors: ethnicity, education, and old age were the major factors involved.
Why would education be a risk? Desmond points to studies showing that education and a stimulating childhood environment increases the number of connections between brain cells. He suggests that when a stroke hits, these extra connections may help educated people compensate better.
Stroke expert Charles P. Warlow, FRCP, professor of medical neurology at University of Edinburgh in Scotland, warns that dementia is not something that occurs overnight, even in stroke patients. In an interview with WebMD, Warlow says that a stroke may exacerbate underlying dementia as well as cause it.
"The rate of dementia in any study depends on how you define it -- it is not something that just happens one day," he says. "Somebody can have a stroke and as a consequence of the stoke has some memory problem. Now how does that qualify as dementia? The time at which you blow the whistle and say 'Now this person has dementia' varies. There are plenty of stroke patients who are demented, and probably the stroke itself has a lot to do with it. The interesting thing is whether stroke accelerates dementia that is going on already."
The most common cause of dementia is Alzheimer's disease (AD), and the current study finds a link to stroke: about a third of the patients who had dementia after stroke also had AD. "There is a closer link between vascular disease and AD than we have been thinking lately," says Marler. He says his agency is working to increase collaboration between stroke and AD researchers.
- According to a new study, one out of every four stroke survivors develops dementia, and the risk is higher among black and Hispanic patients, compared to whites.
- Stroke patients with less education are also more likely to develop dementia.
- Dementia is a disease that develops slowly over time, and researchers are unsure whether stroke exacerbates underlying dementia or actually causes the disease.