August 24, 2011
Two new studies show how scientists are increasingly using brain scans to diagnose Alzheimer’s at an early stage, years before symptoms like memory loss and difficulty in thinking become evident. Early diagnosis can be important, since the brain changes that cause Alzheimer’s can begin to take their toll a decade or more before the disease is suspected and treatment may be most effective at this early stage.
Current Alzheimer’s medications may ease some of the symptoms of the disease but do nothing to stop its downward progression. Doctors would like to develop so-called “disease-modifying drugs” that may slow or halt the course of Alzheimer’s, and it may be particularly important to test them on patients at the earliest stages of the disease, before damage to the brain becomes extensive and irreversible. Early diagnosis also allows more time for patients to consider entering clinical trials and gives families better opportunities to plan for the future.
Both studies used a type of brain scan called magnetic resonance imaging, or MRI, that provides 3-D pictures of the brain. The first study, published in Neurology, from the American Academy of Neurology, confirmed that areas of the brain affected by Alzheimer’s may start shrinking a decade before the disease is diagnosed.
For the study, researchers at Harvard Medical School in Boston and Rush University in Chicago took MRI scans of 65 healthy seniors who were free of serious memory complaints. All were given medical check-ups, including repeat scans, for many years, and in some cases for over a decade. During that time, 15 of them developed Alzheimer’s.
The researchers found that those whose brains shrank the most were much more likely to develop Alzheimer’s than those with larger brains. Among those with the smallest brains at the end of the study period, over half developed Alzheimer’s. None of those with the largest brain measurements developed the disease. Among those whose brains had shrunken a medium amount, about 20 percent developed Alzheimer’s or another form of dementia.
Using MRI scans to measure the brain “is potentially an important imaging marker of early changes in the brain associated with Alzheimer’s disease that could help predict who might develop the dementia associated with this disease and possibly even how long it would be before dementia develops,” said study author Dr. Bradford Dickerson of Harvard. The tests are not routinely performed and more work must be done to confirm the findings, “but we are optimistic that this marker will be useful in the future,” he said.
In the second study, researchers used MRI scans to look at the brains of those with mild cognitive impairment, a form of serious memory loss that sometimes progresses to full-blown Alzheimer’s disease. Each year, around 15 percent of people with MCI develop Alzheimer’s, compared to just 1 to 2 percent among those of the same age in the general population.
The aim was to use the brain scans to try to predict which people would progress to dementia. “Being able to better predict which individuals with MCI are at greatest risk for developing Alzheimer’s would provide critical information if disease-modifying therapies become available,” said the study’s lead author, Linda K. McEvoy, Ph.D., assistant professor in the Department of Radiology at the University of California, San Diego School of Medicine.
The researchers used data from the Alzheimer’s Disease Neuroimaging Initiative, a large study at many medical centers that performed brain scans and other tests on hundreds of elderly volunteers from 2005 to 2010. They found that thinning in the brain’s cortex, an outer region critical for memory, attention, thought and language, was an indicator of progression to Alzheimer’s.
People with mild cognitive impairment who had the most thinning in the cortex during the five-year study had up to a 40 percent chance of progressing to Alzheimer’s, more than doubling the risk. Those with the most rapid-thinning, year over year, had up to a nearly 70 percent chance of progressing to Alzheimer’s.
Again, the scans are not routinely available in doctors’ offices, and more testing must be done. But the findings underline the progress that continues to be made in diagnosing Alzheimer’s at its earliest stages as investigators work to better understand the disease and find a cure.
Sources: Signature MRI Biomarker Predicts AD Demtnia in Cognitively Normal Adults.” Nuerology, Vol. 76, April 14, 2011, pages 1395-1402.
Linda McEvoy, Ph.D., Dominic Holland, Ph.D., Donald J. Hagler, Jr., Ph.D., et al: “Mild Cognitive Impairment: Baseline and Longitudinal Structural MR Imaging Measures Improve Predictive Prognosis.” Radiology, June 2011.