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PET scans and memory tests best predict Alzheimer's

by Brendon Nafziger, DOTmed News Associate Editor | July 02, 2010
PET scans coupled
with word recall tasks
trumped other tests
for predicting Alzheimer's.
Subjects with mild cognitive impairment who get abnormal readings on PET scans and do poorly on a word recall test are almost 12 times more likely to become afflicted with Alzheimer's disease, according to a new study.

The study, published online Wednesday in the journal Neurology, found that a battery of tests, including MRI brain scans and blood biomarkers, were able to help predict dementia risk.

But so-called FDG-PET scans coupled with poor performance on an episodic memory task were the best predictors of mild cognitive troubles progressing into full-blown Alzheimer's dementia.

"We find individually the [tests] were each for the most part useful for predicting conversion to Alzheimer's disease, but some were more useful than others," lead author Dr. Susan M. Landau, a researcher at University of California-Berkeley, told DOTmed News. "And the two most useful were the episodic memory and FDG-PET."

The study followed about 85 patients with mild cognitive problems, who were part of the broader Alzheimer's Disease Neuroimaging Initiative, for close to two years.

The patients were given a series of tests known to be predictive of dementia. Researchers checked for the APOE gene, associated with Alzheimer's, as well as the ratios of biochemical biomarkers derived from cerebral spinal fluid. These included the protein tau, implicated in the neurofibrillary tangles that develop in the brain in Alzheimer's patients, and amyloid beta, which forms plaque in patients' brains.

Patients also got MRI brain scans, to measure the volume of the hippocampus, a region of the brain involved in memory and known to shrink in Alzheimer's patients.

For PET, researchers scanned the patients' brains to measure 18-fluorodeoxyglucose uptake, as glucose metabolism is diminished in dementia. Patients also received a memory test to determine how many words they could recall from a list.

Although many studies have looked at each of these tests in isolation or compared a few against each other, this is the first report to directly compare them all to see which predicts both Alzheimer's and general cognitive decline, the researchers said.

"Each of these tests have independently shown promise in predicting disease progression, however, prior to the Alzheimer's Disease Neuroimaging Initiative, they had never been compared to one another in the same study before," Landau said in a statement.

When looking at all variables together, the researchers found that patients who had diminished glucose metabolism as revealed by the FDG-PET scan and performed poorly on the memory test were 11.7 times more likely to progress from mild cognitive impairment to Alzheimer's dementia.