Drug May Help Diagnose Alzheimer's Earlier

Drug May Help Diagnose Alzheimer's Earlier

Drug May Help Diagnose Alzheimer's Earlier

April 15, 2012 -- An experimental drug called florbetaben may help doctors diagnose Alzheimer's disease earlier in some people with memory problems.

Florbetaben is one of several new radioactive agents that tag the amyloid plaque that builds up in the brains of people with Alzheimer's disease. Others include Amyvid, approved last week by the Food and Drug Administration.

After florbetaben is injected into the brain, the plaques that are a hallmark of Alzheimer's disease -- light up when a patient has a brain imaging scan called positron emission tomography (PET), says Marwan Sabbagh, MD, director of Banner Sun Health Research Institute in Sun City, Ariz.

In late-stage testing, Sabbagh and colleagues compared PET scans using florbetaben taken from 31 people in the months before they died to brain tissue taken at autopsy. The presence of amyloid plaque at autopsy is currently the only way to confirm a diagnosis of Alzheimer's.

The scans correctly identified 100% of people who had plaque at autopsy, but one person who tested positive for plaque did not end up having any -- a small dent in the test’s accuracy.

The findings are scheduled to be presented next week at the annual meeting of the American Academy of Neurology in New Orleans.

Limitations of Testing

By themselves, florbetaben and its cousins will not pinpoint people with Alzheimer's. What they can do is provide skilled doctors one more piece of information that can be used either to make a diagnosis of Alzheimer's -- or rule it out, experts say.

That's because the scans detect amyloid plaque in the brain, not Alzheimer's itself. Although people with Alzheimer's always have amyloid plaque, plaque does mean someone has Alzheimer's.

For people with memory problems, disorientation, and other symptoms of Alzheimer's, a positive scan means there is a "high probability of Alzheimer's or that Alzheimer's is contributing to the patient's [memory problems]," Sabbagh tells WebMD.

A negative scan in a person with symptoms means the probability of Alzheimer's is extremely low, he says.

The most important thing to know about the new tests is that they only should be performed by a skilled doctor with experience in diagnosing Alzheimer's, says Rachelle S. Doody, MD, PhD, director of the Alzheimer's Disease and Memory Disorders Center at Baylor College of Medicine in Houston.

"A diagnosis of Alzheimer's requires lots of bits of information. This is not a revolution for the diagnosis of Alzheimer's but one of those bits of information that can be helpful," says Doody, who was not involved with the work.

The tests should not be performed in people who do not have memory problems and other symptoms of Alzheimer's, she tells WebMD. That's because having amyloid plaques in the brain doesn't necessarily mean that someone has Alzheimer's, she explains.