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Brain Scans Accurately Predict Alzheimer's


NEW YORK (Reuters Health) - Measuring the brain's metabolism through brain scans known as PET may catch many cases of Alzheimer's disease, even before significant symptoms emerge, US researchers report.

In their study of 284 patients with symptoms of dementia, PET scans showing lowered glucose (sugar) metabolism in certain brain regions predicted most of the Alzheimer's cases that developed over the next 3 years.

Previous research has suggested it is possible to spot Alzheimer's through metabolism patterns on PET scans. But this study shows it can actually work in practice, the study's lead author told Reuters Health.

``Studies before have shown the capability of PET.... What hasn't been available is a good estimate of just how accurate PET is,'' according to Dr. Daniel H. S. Silverman of the University of California, Los Angeles.

Silverman's team found that a single PET scan showed good accuracy among their study patients. It spotted Alzheimer's and other types of neurodegeneration 94% of the time--although 27% of the scans that indicated Alzheimer's were actually falsely positive.

In addition, PET scans were just as accurate among 55 patients who had ``questionable or mild'' dementia at the study's start--75% of whom turned out to have Alzheimer's, the researchers report in the November 7th issue of The Journal of the American Medical Association.

Using PET (for positron emission tomography) allows doctors to visualize the rate of sugar metabolism throughout the brain. An impaired metabolism in certain brain regions has been linked to Alzheimer's, a progressive type of dementia that is marked by cell death and abnormal protein deposits in the brain.

The fact that 94% of true Alzheimer's cases were caught in this study suggests that a negative PET scan should be reassuring to patients--at least as far as their odds of developing the disease over the next few years, according to Silverman's team. However, since there was a sizable number of false-positives, they add, ``a positive scan should not in itself be interpreted as a forerunner of certain progression.''

Indeed, Silverman said PET scans will not become a general screen for Alzheimer's disease, but instead could be used in combination with other tests to distinguish memory loss, behavioral changes and other early symptoms of the disease from those of other conditions, such as depression.

Catching Alzheimer's early is important, he noted, because treatment options have surfaced in recent years. Drugs called cholinesterase inhibitors, for example, have been found to slow the progression of the disease in some patients.

``But if you wait too long (to start the drugs),'' Silverman said, ``you won't get the benefit.''

There remains no cure for Alzheimer's disease, however. As the populations in many countries continue to age, experts predict that the number of people diagnosed with Alzheimer's will reach epidemic proportions.

SOURCE: The Journal of the American Medical Association 2001;286:2120-


Reference Source 89

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