OAK BROOK, Ill.-- According to a study in the September issue of Radiology, the amount of blood flowing into the brain may play a larger role in the development of dementia than previously believed.

Researchers from Leiden University Medical Center in the Netherlands used magnetic resonance imaging (MRI) to examine the brains of elderly patients with and without dementia related to Alzheimer's or Parkinson's disease. As expected, MR images showed that the patients with late-onset dementia had more brain damage compared with young adults and with seniors who had optimal cognitive function. But researchers found that the late-onset dementia group also had a much lower rate of blood flow to the brain than the other two groups.

"Our findings not only support the hypothesis that vascular factors contribute to dementia in the elderly, they are highly suggestive that a diminished cerebral blood flow indeed causes brain damage," said Aart Spilt, M.D., a Leiden radiology resident and lead author of the study. "This gives us a clue to the genesis of dementia."
Dementia is a loss of cognitive functions, such as thinking, remembering and reasoning, that interferes with normal activities. Although many conditions can produce these symptoms, Alzheimer's disease is the most common cause of dementia. Some patients with Parkinson's disease also develop dementia.

Figure 1. Individual estimates of normalized peak MTR in young subjects, elderly subjects with optimal cognitive function, and elderly subjects with dementia. Horizontal lines indicate the group mean.

In the Dutch study, researchers examined 17 patients with late-onset dementia (dementia occurring after age 75), another 16 seniors of the same age with optimal cognitive function and 15 healthy younger individuals. Researchers used MRI to measure cerebral blood flow and the extent of structural brain damage in each person and then compared the results of the three groups.

Average total cerebral blood flow in the healthy young individuals was 742 milliliters (mL) per minute. Cerebral blood flow in the two elderly groups averaged 496 mL per minute, or 246 mL per minute lower than the younger group. In patients with dementia, average cerebral blood flow was 443 mL per minute, or 108 mL per minute lower than seniors of the same age with optimal cognitive function (551 mL per minute).

Although patients with dementia have been shown to require less cerebral blood flow as the brain becomes less active, Dr. Spilt's research provides some evidence that the decreased blood flow may lead to some types of dementia.

"The findings emphasize the importance of monitoring both high and low blood pressure in older adults," Dr. Spilt said. "Possible causes of low cerebral blood flow include heart failure and a narrowing of cerebral or cervical arteries."

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