21 Dec 2006

New scan spots dementia

A new imaging technique could make it possible for doctors to detect Alzheimer's disease in the brain before extensive damage has taken place, researchers report.

A study in the December 21 issue of the New England Journal of Medicine details the use of a new imaging molecule dubbed FDDNP that literally stains the diseased brain tissue so it shows up on PET scans. Scientists from the University of California, Los Angeles, were then able to distinguish people with normal brains from those with mild cognitive impairment and those with Alzheimer's disease.

"I think this approach offers considerable promise for a brain test that might be used to detect who would benefit from future treatments," said study author Dr Gary Small, director of the Centre on Ageing and a professor at the SEMEL Institute for Neuroscience and Human Behaviour at UCLA.

May boost prevention
"There is hope," Small said. "We are developing a technique that may not provide a cure, but may offer the next best thing - identifying the problem before extensive brain damage and impairment in everyday life begins. It will likely be easier to protect a healthy brain than repair one that's already been damaged."

Alzheimer's disease is a degenerative brain disorder that eventually robs people of their memories as well as their ability to reason, communicate and care for themselves.

There is currently no easy way to diagnose Alzheimer's disease, especially in its early stages. The only definitive way to diagnose the disorder is to autopsy the brain after death to see if the signs of Alzheimer's disease - abnormal protein fragments called plaques and tangles - are present.

Molecule clings to plaques and tangles
That's where this latest research comes into play. The new molecule, FDDNP, secures itself to plaques and tangles in the brain, so they can be seen on positron emission scanning (PET).

To get an idea of whether or not this technique could be used to detect Alzheimer's disease in its earlier stages, Small and his colleagues conducted PET scans using FDDNP on 83 people. Twenty-five were suspected to have Alzheimer's disease, 28 were thought to have mild cognitive impairment, and 30 people had no cognitive problems.

All of the study volunteers also underwent magnetic resonance imaging (MRI) or computerized tomography (CT) scans for comparison.

The researchers found that PET scans using FDDNP were more accurate than standard PET scans, MRI and CT scans at detecting the differences between normal, mildly impaired and Alzheimer's brains.

Small said that they were able to follow some of the study volunteers for several years, and that those who got worse over time had FDDNP binding values (the amount of FDDNP that clung to plaques and tangles) that increased between 5 percent and 11 percent. Those whose cognitive condition remained relatively unchanged had very small changes in FDDNP binding values, Small said.

Additionally, one of the Alzheimer's volunteers died during the study period and, on autopsy, the researchers found the areas of the brain clogged with plaques and tangles were stained with FDDNP.

Not for screening tests
Small said he doesn't believe this technique could be used as a screening test, at least not until there were an effective treatment to alter the course of the disease. But, he said, it could be quite useful for clinical trials, because it could give researchers a quick and easy measure of how effective a treatment might be.

"This study is a small window into a much bigger story. Advanced imaging technologies - including PET, MRI and others - have great potential to improve early detection of Alzheimer's disease and may prove to be powerful tools in testing new therapies," said Dr William Thies, vice president of medical and scientific relations for the Alzheimer's Association.

"A sensitive and accurate method for early Alzheimer's diagnosis that can also track the progression of the disease would help us treat people earlier and greatly speed testing of new drugs in treatment trials. Not having such a test is a major roadblock to efficient drug development," said Thies.

Thies pointed out that FDDNP isn't the only new technique coming down the pipeline. Another molecule, dubbed the Pittsburgh Compound B (PIB), works in a similar manner on PET scans, though Small said that PIB isn't as easy to produce as FDDNP, and PIB only binds to plaques, not to tangles. That, he said, could be an important difference, because previous research has shown that tangle build-up accelerates as mild cognitive impairment worsens. – (HealthDayNews)