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Nov. 9 - PET Scan Distinguishes Alzheimer's From Other Dementia

A PET scan that measures uptake of sugar in the brain significantly improves the accuracy of diagnosing a type of dementia often mistaken for Alzheimer’s disease, a study led by a University of Utah dementia expert has found.

The scan, FDG-PET, helped six doctors from three national Alzheimer’s disease centers correctly diagnose frontotemporal dementia (FTD) and Alzheimer’s in almost 90% of cases in the study—an improvement of as much as 14% from usual clinical diagnostic methods. FDG stands for fluorodeoxyglucose, a short-lived radioactive form of sugar injected into people during PET scans to show activity levels in different parts of the brain. In Alzheimer’s, low activity is mostly in the back part of the brain; in FTD, low activity is mostly in the front of the brain.

FDG-PET is an especially powerful tool in early treatment of FTD, said the study’s lead author, Norman L. Foster, MD, professor of neurology and director of the Center for Alzheimer’s Care, Imaging and Research at the University of Utah School of Medicine. The study has appeared online in the journal Brain.

Foster and his colleagues examined the medical records and FDG-PET scans of 45 patients who later had autopsies. Microscopic examination found 31 had Alzheimer’s and 14 had FTD. The researchers summarized the clinical course of the disease in each patient. The expert neurologists at the NIH centers, who had 10 years to 25 years of experience, then were asked to decide what caused each patient’s dementia using clinical information alone or using FDG-PET images.

The experts correctly distinguished FTD and Alzheimer’s using only the clinical methods in 76% to 79% of the cases. Using the FDG-PET scans alone, however, the physicians correctly diagnosed the two dementias in 85% to 89% of cases. Adding FDG-PET to clinical information increased the correct diagnosis from 79% to 90%. The highest accuracy in diagnosis was achieved with SSP (stereotactic surface projection) displays, which summarize changes in brain activity and apply a statistical test to show significant areas of damage.

The PET scans also had other benefits. The researchers found in 42% of cases, the scans increased the experts’ confidence in a correct diagnosis or made them question and sometimes change an incorrect diagnosis.

Source: University of Utah Health Sciences Center

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