Reston, Va.-Researchers involved in a large, multi-institutional study using positron emission tomography (PET) imaging with the radiotracer fluorodeoxyglucose (FDG) were able to classify different types of dementia with very high rates of success, raising hopes that dementia diagnoses may one day be made at earlier stages.

"Previously, scientists have been able to look only at the surface of the brain to differentiate various types of dementia," said Lisa Mosconi, Ph.D., assistant professor of psychiatry at the New York University School of Medicine. "With FDG PET, we were able to develop standardized disease-specific patterns from which we could correctly classify dementia more than 94 percent of the time."

The study, which was reported in the March issue of the Journal of Nuclear Medicine, measured the cerebral metabolic rate of glucose (CMRglc)-the amount of sugar the brain uses to fuel its activities-in various areas of the organ. A decrease in this rate is indicative of a loss of nerve cells and of dysfunction associated with dementia. Because FDG behaves like glucose when injected into the body, its location in the PET scans pinpointed the specific area where glucose utilization had fallen below normal levels as compared to an age-appropriate control group.
"Each type of dementia examined-Alzheimer's disease (AD), frontotemporal dementia (FTD), and dementia with Lewy bodies (DLB)-affects a different area of the brain. Based on where in the brain this decrease occurred, we were able to determine which type of dementia a patient had," Mosconi explained.

For instance, only AD patients have severe CMRglc reductions in the hippocampus (a part of the brain located deep in the organ and, prior to this study, unreachable for examination), whereas FTD patients have only mild abnormalities in the area and DLB patients have no hippocampal hypometabolism. "We believe that the ability to measure this embedded area in the brain will be important in identifying AD at an early stage," added Mosconi.

This is also the first study to use FDG PET to compare an early stage of dementia known as mild cognitive impairment (MCI) with dementing diseases other than AD. According to the researchers, the results suggest that the ability to detect differentiated uptake of glucose may result in earlier and more accurate diagnoses of MCI and better disease management.

"Because the incidence of these disorders is expected to increase dramatically as the baby-boomer generation ages, accurate diagnosis is extremely important-particularly at the early and mild stages of dementia when life-style changes and therapeutic interventions would be most effective," said Mosconi.

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