PET Scans May Help With Alzheimer's Diagnosis

Studies Show PET Scans May Be Useful Tool in Detecting Alzheimer's

July 11, 2011 -- A special type of positron emission tomography (PET) scan may help detect the plaques in the brain associated with Alzheimer's disease, two new studies show.

The studies are published in the Archives of Neurology.

The special PET scans use radioactive tracers to highlight amyloid protein plaques in the brain, which are a hallmark of Alzheimer's disease. They may allow doctors to diagnose Alzheimer's earlier -- even before any symptoms appear. But many people with amyloid plaques in their brain don't have Alzheimer's disease.

A progressive brain disease that leads to a decline in memory and other cognitive abilities,Alzheimer's disease is the most common form of dementia. According to the Alzheimer's Association, 5.4 million Americans have Alzheimer's disease in 2011, a figure that includes one in eight Americans older than 65.

One study shows that PET imaging using florbetapir F 18 as a tracer was able to distinguish between 68 people with suspected Alzheimer's disease, 60 people who showed signs of mild cognitive impairment, and 82 healthy older people with no signs of cognitive impatient.  

The other study looked at PET scans using fluorine 18-labeled flutemetamol tracer among seven people with normal pressure hydrocephalus, a progressive condition that causes dementia and often mimics Alzheimer's disease. These study participants had undergone brain tissue biopsies during a procedure to treat normal pressure hydrocephalus. Biopsy results correlated with those seen via PET scans.

"What you see on the scans directly reflects the amount of amyloid protein in the brain," says Adam S. Fleischer, MD, a neurologist from Banner Alzheimer's Institute in Phoenix. Fleischer is a researcher on the florbetapir F 18 study.

It is not always that straightforward, he says. Up to one-third of people older than 65 will have amyloid protein in their brains and no cognitive impairment, he says.

"It is not clear how amyloid imaging in the brain will predict whether or not you will develop Alzheimer's disease," Fleischer says. "If you have amyloid in your brain and dementia, it's highly or most likely that your memory problems are from Alzheimer's disease."

Highly likely does not mean 100%, he says.

The tests may ultimately help rule out Alzheimer's disease, instead of rule it in, Fleischer says.

"If you don't have amyloid protein in your brain, even if you have dementia, it's not Alzheimer's disease," he says. "It's a slam dunk."

Many drug companies are working on drugs that target amyloid plaques in the brain, and the only way to determine if these drugs are effective is with this screening technology, he says.

"Before we had to wait for symptoms, but now we can see if there is evidence that these drugs are removing amyloid," he says.

Dementia is a late stage of Alzheimer's disease, he says. "The pathology starts in the brain 10 to 20 years before symptoms," he says. "We need ways to identify early Alzheimer's disease in living patients and that is where amyloid imaging comes into play."

Protein Levels in Spinal Fluid May Spot Alzheimer's

Study Suggests Potential for New Test to Detect Early Alzheimer's Disease

June 22, 2011 -- High levels of a protein in the spinal fluid of older people with mild memory loss may help predict which patients will develop Alzheimer's disease, a study shows.

The study by researchers at Germany's Technical University Munich looked at levels of amyloid precursor protein (APPB) in patients with mild cognitive impairment (MCI), a condition indicating some memory problems but not enough to be classified as dementia. The researchers found that high levels of APPB were linked to the patients’ later development of Alzheimer's.

Elevated AAPB in combination with elevated tau protein, which indicates brain cell damage, was roughly 80% accurate in predicting Alzheimer's disease progression in elderly patients who entered the study with mild cognitive impairment (MCI).

If the findings are confirmed, cerebrospinal fluid APPB could help identify patients who will benefit from emerging Alzheimer's treatments very early in the course of their disease, study researcher Robert Perneczky, MD, tells WebMD.

"With a little luck we will have effective disease-modifying therapies for Alzheimer's disease in just a few years," he says. "These treatments will have the greatest benefit for patients who start them very early in the disease process, and we need effective biomarkers to identify these patients."

About 15% of older patients with a diagnosis of mild cognitive impairment (MCI) will progress to Alzheimer's disease over the course of a year.

But some patients never progress, and others experience improvements in memory.

Established biomarkers help distinguish Alzheimer's disease from other causes of memory decline, such as depression, but they have not proven very useful for predicting progression to Alzheimer's in people with few symptoms, Perneczky says.

In their effort to determine if amyloid precursor protein improves the predictive ability of the established biomarkers, Perneczky and colleagues took samples of cerebrospinal fluid from 58 patients with mild cognitive impairment and then followed the patients for three years.

The fluid was tested for levels of APPB, as well as tau protein and other markers.

During the follow-up, 21 study participants developed Alzheimer's disease, 27 retained the diagnosis of MCI, and eight patients experienced improvements in memory.

The average APPB levels for patients who progressed to Alzheimer's were significantly higher than for patients who did not progress.

The best predictor of whether an MCI patient would develop Alzheimer's was that patient's age, combined with tau protein and APPB levels.

When these three factors were combined, the results were roughly 80% accurate in predicting progression to Alzheimer's disease.

The study appears in the June 22 online edition of the journal Neurology.

"This is clearly better than what we have seen with the established biomarkers," Perneczky says, adding that the next step is to confirm the findings and determine if APPB is useful for predicting cognitive decline in healthy older people with no evidence of memory decline.

If future trials prove promising, spinal taps may become a routine screening test for older people to identify those at risk for developing Alzheimer's long before memory loss occurs, neurologist Roger N. Rosenberg, MD, tells WebMD.

Rosenberg directs the Alzheimer's Disease Center at the University of Texas Southwestern Medical Center.

"It may be fair to say that we can't really treat Alzheimer's," he says. "The hope is that we will be able to treat those at risk to prevent the cognitive declines from happening, but we have to identify them first."