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