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PET Scans Highly Reliable in Detecting Alzheimer's

Technology: Screening can predict which patients' memory problems will develop into the disease.


Doctors and patients have long needed a way to diagnose Alzheimer's disease when memories first fail and speech falters. Now a screening technique that had looked promising has been shown to be highly reliable.

New research from UCLA and seven other academic centers confirms that PET scans of the brain not only can diagnose Alzheimer's in its earliest stages, but can also predict which patients' memory problems will develop into Alzheimer's or related types of dementia.

The findings have given many experts in the field the kind of evidence they've long awaited. "It's about time," said Dr. Zaven Khachaturian, medical and scientific advisor to the Alzheimer's Assn.

With an early Alzheimer's diagnosis, patients will be able to take medications that can stave off some of the debilitating symptoms, and thus delay their need for nursing care. "You'll be able to tell a patient something terrible is going to happen in their life, but they'll have five, 10, 20 years to put their life in order," Khachaturian said.

Until now, the only definitive way to diagnose Alzheimer's was after death, through an autopsy that revealed plaques and tangles inside the brain. As a result, most doctors relied on a clinical evaluation that included memory and language tests, blood tests, a physical exam and perhaps another type of scan to rule out other diseases. Together, those evaluations were correct about 65% of the time in identifying whether a patient had Alzheimer's.

Although small studies (the largest with only 22 patients) had shown that PET scans could detect Alzheimer's disease, the new research--based on scans of 284 middle-aged and elderly people with possible dementia--showed the technique to be extremely reliable. It detected early Alzheimer's disease in up to 95% of cases.

The latest findings, from an international team led by Dr. Daniel H. Silverman, an assistant professor of molecular and medical pharmacology at UCLA, appeared in the Nov. 7 issue of the Journal of the American Medical Assn. "The test should be used in patients who have had first-line screening and don't have a satisfactory solution to the problem, as opposed to 'wait and see and come back in a year,"' Silverman said. "If you haven't had your symptoms fully explained and fully reversed in six months, you would be a candidate for PET."

A PET (positron emission tomography) scan maps activity in the brain by showing how much glucose, a sugar, is metabolized in particular regions. When activity in a brain area declines, as with Alzheimer's and other degenerative diseases, metabolism there drops. Each of the various brain disorders has a distinctive pattern. For example, in Alzheimer's, doctors see more decline in regions toward the back of the brain, which would appear in blue and violet in the PET scan image, whereas healthy areas would turn up in red, orange and yellow.

However, access to the test remains problematic. PET scans, which cost an average of $1,500, aren't available everywhere and aren't routinely covered by private insurance or Medicare for dementia evaluation, said Dr. Jeffrey L. Cummings, director of the UCLA Alzheimer's Disease Center.

He says that he uses them frequently but that many of his patients can afford to pay for the tests themselves. "One of the important issues that this article raises is to suggest that the data are now sufficiently good that this scan can be useful, that it should be reimbursed by Medicare," he said.

Cummings, a study co-author, said that with an Alzheimer's diagnosis and appropriate treatment, "we can delay nursing home placement on average two years. Nursing homes in California cost almost $50,000, so we're talking about saving $100,000 worth of nursing home placement time."

The new findings are likely to increase use of PET scans as an Alzheimer's diagnostic tool.

Dr. Eric Reiman, director of the Arizona Alzheimer's Disease Center in Phoenix and an Alzheimer's expert not involved with the study, said that until now, he's been fairly conservative in using PET scans, reserving them for just a few patients where the uncertainty about their illness becomes disabling to patient and family. "This article suggests ... maybe one should use this more routinely."

He suggested that the study results were so strong that they could alter recently updated guidelines from the American Academy of Neurology, which called PET promising in Alzheimer's diagnosis, but did not recommend routine use of the screening in patients with suspected dementia.

Currently, the tests are used primarily by neurologists, psychiatrists and others who specialize in memory disorders. But Dr. Alan Jay Fischman, director of nuclear medicine and the PET laboratory at Massachusetts General Hospital in Boston, predicted the scans could become a tool for primary-care doctors with elderly patients.

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