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New Tool to Diagnose Alzheimer's

A newly identified imaging compound that shows how Alzheimer's disease ravages the brain could lead to better tools to diagnose the disease and better ways to evaluate new treatments.

In brain imaging studies, the compound, known as FDDNP, bound to the plaques and tangles within the brain that are the characteristic features of Alzheimer's disease. Brain imaging with FDDNP proved to be more effective than other imaging methods for identifying patients with the disease.

Brain imaging is mainly used in the evaluation of Alzheimer's to rule out other causes of mental decline.

It is much less effective for identifying the nerve fiber tangles and protein deposits called plaques that occur in the brains of patients with the disease.

"At least in this study, we showed that this method is an accurate diagnostic tool," researcher Gary Small, MD, tells WebMD. "But even more important, I think, is its potential role in the search for Alzheimer's treatments."

Roughly 4.5 million Americans have Alzheimer's disease, and that number is expected to triple by 2050 as the U.S. population ages.

Identifying brain changes in people who will go on to develop Alzheimer's before they show symptoms of the disease has been a top priority of researchers in the field.

Comparing Diagnostic Tools

Positron emission tomography (PET) is an imaging technique that combines a radioactive tracer with a molecule. The combination is injected into the body, and as the molecule collects in certain tissues of the body, the tracer shows up on a scanning device.

In the new study, Small and colleagues assessed the ability of PET imaging using the molecule FDDNP to identify Alzheimer's patients.

Eighty-three middle-aged or elderly volunteers with self-reported memory problems were included in the study. Using standard diagnostic methods, 25 of the study participants were diagnosed with Alzheimer's disease and 28 with mild mental impairment. Thirty were found to be mentally fit.

When compared with PET scanning using the standard molecule FDG, the FDDNP scanning technique was found to be more accurate for detecting differences among the study participants.

FDDNP PET scan was able to differentiate patients with Alzheimer's from those with mild mental impairment or no impairment better than the FDG PET scan or MRI scan.

Follow-up of the volunteers, conducted two years after initial testing, showed that FDDNP scans continued to correlate well with clinical symptoms.

The study by researchers with the University of California, Los Angeles, was supported by the National Institute on Aging. It is published in the Dec. 21 issue of The New England Journal of Medicine.

Better Treatments, Earlier Interventions

Small says the technique may even prove useful for identifying and assessing therapies that prevent Alzheimer's disease.

"It may be possible to identify people who are not yet symptomatic and who would potentially get the most benefit from early interventions."

The more immediate promise is to further the search for better ways to treat people who already have Alzheimer's, says Susan Molchan, MD, a National Institute on Aging official.

"The hope is that better imaging techniques and markers will allow us to conduct clinical trials with fewer volunteers and in less time," she says.

Molchan tells WebMD that while there are still many unanswered questions about FDDNP imaging, the technique should prove to be a useful research tool.

"This type of scanning should give the people who are developing new therapies an early signal of how well those therapies work," she says.

SOURCES: Small, G.W. The New England Journal of Medicine, Dec. 21, 2006; vol 355: pp 2652-2658. Gary W. Small, MD, professor of psychiatry and biobehavioral sciences; director, UCLA Center on Aging, David Geffen School of Medicine, UCLA Susan Molchan, MD, program officer, National Institute on Aging Neuroscience and Neuropsychology of Aging Program. Wikipedia: "Positron Emission Tomography."

By Salynn Boyles
Reviewed by Louise Chang