In the vast majority of cases, researchers can distinguish between Alzheimer's and another form of dementia with shared symptoms by using a specific type of PET (positron emission tomography) scan that looks for evidence of plaque in the brain, recent research suggests.

Known as the "PIB PET" scan, this type of scan appears to be more accurate in telling apart the two types of dementia than the more commonly used "FDG PET scan.

"These two types of dementia share similar symptoms, so telling the two apart while a person is living is a real challenge, but important so doctors can determine the best form of treatment," study author Gil Rabinovici, MD, of the University of California, San Francisco Memory and Aging Center, explained in a university news release.

The study was published in an online issue of Neurology.

How The Scan Works

The PIB PET scan harnesses a "PIB marker" to uncover signs of brain plaque (known as amyloid). The presence of such plaque is a telltale sign of Alzheimer's, but is not a signal of another type of dementia called frontotemporal lobar degeneration (FTLD).

In FTLD, the frontal and temporal lobes of the brain atrophy. It's less common than Alzheimer's, but equally as devastating. People with FTLD can develop erratic behavior, emotional problems, trouble communicating and difficulty with walking and other basic movements.

To gauge the effectiveness of PIB PET scans, the team focused on 107 patients who either had early onset Alzheimer's or PTLD.

All the patients underwent both the PIB PET scan and the FDG PET scan. The latter looks for signs of metabolic changes in the brain.

The Results

While the FDG PET scan was found to accurately differentiate between the two forms of dementia nearly 78% of the time, PIB PET scans did so nearly 90% of the time.

Although the study found that FDG PET resulted in fewer false positives in select situations, overall, PIB PET appeared to perform better.

"While widespread use of PIB PET scans isn't available at this time, similar amyloid markers are being developed for clinical use, and these findings support a role for amyloid imaging in correctly diagnosing Alzheimer's disease versus FTLD," Dr. Rabinovici noted.

Expert Reaction

Catherine Roe, PhD, an assistant professor of neurology with the Knight Alzheimer's Disease Research Center at Washington University School of Medicine in St. Louis, said that currently PIB PET technology is impractical to deploy outside of specialized research institutions. But that, she noted, is about to change.

"The authors are correct in saying that new amyloid marking technology is being developed right now that will be easier to use in a clinical setting," she said. "Testing is under way. So based on their findings, their support for the use of this type of scan makes really good sense to me. Because 90% sensitivity in correctly identifying disease is a lot better than 78%."

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