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Brain Scan can Diagnose Alzheimer's Disease

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Updated December 07, 2003

November, 2002. Even though Alzheimer's disease takes a terrible toll on the memories and lives of millions of adults each year, doctors often face great uncertainty when trying to diagnose it in living people. Several other diseases can mimic the symptoms of Alzheimer's disease, and only an autopsy can confirm a diagnosis for certain.

The lack of a definitive Alzheimer's test didn't matter so much in the past, but in recent years new drugs and therapies have been shown to slow the spiral of memory loss and behavior changes that Alzheimer's patients face. A good new diagnostic test could help patients get help early -- and make the most of their remaining years.

That's why University of Michigan Health System researchers and others are so excited about a kind of medical imaging that they think can tell Alzheimer's disease apart from other disorders. By looking at the brain with a special camera, they hope to give patients a more definitive diagnosis while they can still do something about it.

The "camera" in question is really a machine called a PET scanner; PET stands for positron emission tomography. Doctors already use PET to find cancer and heart problems, but a team led by U-M researchers recently released the first conclusive study showing it could be used to tell Alzheimer's disease from other disorders.

"PET scanning is a way to look at the brain in people who are living and dealing with their disease," says Norman Foster, M.D., the U-M neurologist leading the research team. "The PET machine looks very much like an MRI or CT scanner, but it's different because it can show not just what the brain looks like inside the head, but how active different parts of the brain are and how they're reacting to the disease."

This brain activity -- or lack of it -- is what matters in Alzheimer's disease, adds Foster, who directs the Cognitive Disorders Clinic at the U-M Geriatrics Center and is a professor in the U-M Department of Neurology and associate director of the Michigan Alzheimer's Disease Research Center.

In Alzheimer's patients, many of the brain's nerve fibers are lost, and an abnormal buildup of protein damages nerve cells. Though the causes are mostly unknown, save for a suspected genetic link in some cases, the effects are all too apparent. Patients who start out with absentmindedness and mild memory loss worsen to become restless, moody, anxious, and confused, with increasing memory loss. In the final stages, patients often lose the ability to talk to others or care for themselves.

Initial results were presented recently at the International Conference on Alzheimer's Disease and Related Disorders. Based on the U-M study, and other evidence, Foster feels that earlier diagnosis with PET could become a common practice within a few years, and help guide treatment.

Experts estimate that 3 million to 4 million Americans have some form of Alzheimer's disease. But the exact number is unknown due to difficulty in diagnosis, especially in the early stages.

Doctors often use checklists of symptoms, and other behavioral assessment tools, to help them try to detect Alzheimer's. But such methods can produce major variations in medical opinion about a single patient. Adding to the confusion are a group of related disorders -- all called dementias -- which all share common symptoms of declining intellectual abilities.

"Alzheimer's disease can be mimicked by many other similar illnesses. And in some cases, memory loss isn't the first symptom -- it could be behavioral or language changes, or difficulty with everyday activities," Foster notes. "All of these can be caused by different conditions that require different kinds of treatments and may or may not respond to the same medications."

As big as the problem is now, experts expect the number of Americans with Alzheimer's disease to grow to as many as 7 million in coming decades, as the population ages. So the need for a good diagnostic test -- and better treatments -- will only get more pressing.

Researchers have already tried using other medical imaging techniques to detect the disease, with disappointing results. Up to now, magnetic resonance imaging (MRI) and computed tomography (CT) scans only rule out other disorders -- they can't positively detect Alzheimer's.

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