Two forms of dementia that are often confused with each other can be distinguished with a high degree of accuracy using a special positron emission tomography (PET) scan that measures the brain's sugar uptake, according to research by a University of Utah dementia expert.

The scan, called an FDG-PET, involves injecting fluorodeoxyglucose, a short-lived radioactive form of sugar, into a PET scan subject to map activity levels in different parts of the brain. The two types of dementia — Alzheimer's and frontotemporal dementia (FTD) — are often hard to differentiate. But while Alzheimer's affects the back part of the brain, impacting memory and spatial thinking, FTD more often affects the front of the brain and language.

With the FDG-PET scan, six doctors from three national Alzheimer's disease centers, including the U.'s Center for Alzheimer's Care, Imaging and Research, could correctly identify the type of dementia in almost 90 percent of cases — as much as a 14 percent improvement over what they did using clinical diagnostic methods alone. The study appeared online in the journal Brain.

It's important to distinguish between Alzheimer's and FTD — two of the three most common of more than 70 types of dementia — because their natural courses can differ, and so can symptoms. As more treatments are developed — FTD treatment just deals with symptoms, there are few effective treatments for Alzheimer's and there is no cure for either — knowing which type of dementia a person has will be even more important, said Dr. Edward Y. Zamrini, associate professor of neurology and director of clinical trials for the U.'s Alzheimer's center.

"It makes sense to treat the right disease with the right medication," he said.

Alzheimer's typically affects people after age 65, although a subset have early onset. For every five years over age 65, the risk of developing it doubles. FTD can affect people in their 40s and 50s, although it's less common overall than Alzheimer's. And FTD is much more likely to be familial, an important fact for people who want to know their risk.

Areas of the brain that are thick or that have lost connections are not going to use up as much of the glucose, which will be visible on the scan.

The study's lead author, Dr. Norman L. Foster, professor of neurology and director of the U.'s Alzheimer's center, called the scan a powerful tool for early treatment of FTD, which besides striking younger people is marked by behavioral changes and trouble with language. It, too, can take years to develop.