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PET Scans May Improve Alzheimer's Diagnosis

They cut unneeded drugs, reduce nursing home time

FRIDAY, Oct. 4, 2002 (HealthDayNews) -- Using positron emission tomography (PET) to diagnose Alzheimer's disease can cut down on unnecessary medications and reduce nursing home time, researchers say.

A team from the University of California at Los Angeles analyzed two approaches to the diagnosis of Alzheimer's disease. One used the recommendations set down last year by the American Academy of Neurology, which suggests a physician perform mental status exams, memory impairment screens, and other tests. The other used those same recommendations but also added PET scans to the workup.

A PET scan measures the brain's metabolic pattern and can help determine whether early Alzheimer-type damage has set in, the UCLA team has previously found.

"More patients would be accurately diagnosed in the early stages if they have PET," says Dr. Daniel Silverman, lead author of the study, which is published in the current issue of the journal Molecular Imaging and Biology.

Silverman is not saying that everyone suspected of having Alzheimer's Disease needs a PET scan. And another expert in the field says he is not yet convinced that PET scans are a vital part of a workup for Alzheimer's.

But in appropriate patients, Silverman says, a PET scan can be a boon. To determine the role that PET scans play, Silverman's team made what researchers call a modeled comparison between the two diagnostic strategies. The team examined the best current medical literature endorsed by the Academy on Alzheimer's and found that for every 100 patients with early cognitive decline, the literature showed that conventional methods would have mistakenly attributed the symptoms to Alzheimer's 23 times and overlooked early Alzheimer's eight times.

Then the researchers used a technique called clinical benefit-risk analysis to see what effect PET scans would have if added. They found PET would have prevented 11 of the 23 incorrect diagnoses and would have prevented five of the eight false negatives.

The PET scan, Silverman says, "reduces the false positives [in diagnosis] from 23 percent to 12 percent and it reduces the false negatives from 8 to 3 percent. What that converts to in terms of outcome is cutting months of unneeded drug treatment in half and the avoidable months of nursing home care by about 60 percent."

In a previous study, the UCLA team found that PET scans image brain changes associated with Alzheimer's and find the changes about 93 per cent to 95 percent of the time when they are present.

The take-home point for physicians and consumers, Silverman says, is not to request a PET scan if they vaguely suspect they have Alzheimer's. He recommends that anyone who suspects they have Alzheimer's first find a geriatric psychiatrist or neurologist and that the doctor follow the academy guidelines for diagnosis.

"If after that evaluation the diagnosis is not clear or if they have not had treatment that causes complete reversal of symptoms to normal, at that stage they could be a candidate for PET," Silverman says.

Another expert calls the new study interesting, but he says he is not yet sure PET scans should be incorporated into the diagnosis of Alzheimer's. "At this point, the field is not convinced of the need for PET scans," say Bill Thies, vice president for medical and scientific affairs for the Alzheimer's Association.

"There is a relatively small amount of data," he says. "And while the folks who wrote this paper have collected as big a series as is currently available, there are still some missing elements, particularly the ability to track the disease in multiple [diverse] populations."

Because there is not yet a definitive treatment to stop Alzheimer's, early identification is not as useful as it might be in the future, he adds. He calls the use of PET scans for Alzheimer's "an evolving debate. Like a lot of other debates in medicine, it's going to go on for a while before we come to a conclusion."

What To Do

For information on Alzheimer's disease, try the Alzheimer's Association and the Alzheimer's Disease Education and Referral Center.

SOURCES: Daniel Silverman, M.D., Ph.D., head of neuronuclear imaging research group, and assistant professor of molecular and medical pharmacology, University of California, Los Angeles, School of Medicine; Bill Thies, Ph.D., vice president of medical and scientific affairs, Alzheimer's Association, Chicago; July-August 2002 Molecular Imaging and Biology
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