Alzheimer’s disease is the most common form of dementia , afflicting up to four million Americans. The risk for developing Alzheimer’s disease increases with age, and half of all people age 85 and older have the disease.

Alzheimer’s disease progresses slowly. It usually begins with subtle but measurable memory problems, called mild cognitive impairment (MCI), and ends with severe brain damage. People with MCI have ongoing memory problems, but they do not exhibit other symptoms of dementia like impaired judgment or reasoning. They also do not show significant impairment in their activities of daily living. People with MCI decline to dementia at a rate of 10% to 15% annually, compared with a rate of 1% to 2% among healthy elderly people. As researchers find out more about MCI, they hope to prevent or delay further memory loss and progression to Alzheimer’s disease.

A new study in the December 2003 issue of Radiology found that using magnetic resonance imaging (MRI) to track subtle changes in the brain accurately predicted future MCI in 40 of the 45 healthy adults who participated in the study.

About the Study

Forty-five healthy participants over the age of 60 underwent MRI exams and tests for cognitive functioning before the study began, and every two years thereafter.

Using an automated procedure, the researchers compared baseline MRIs with the first follow-up MRIs to detect subtle changes (atrophy) in both the whole brain and in a specific, memory-related region of the brain (the medial temporal lobe, or MTL).

At the end of six years, the researchers divided the participants into two groups: those who remained cognitively healthy and those who experienced cognitive decline. Then the researchers calculated whether brain changes seen in the MRIs predicted cognitive decline.

The Findings

After six years, 13 (29%) of the participants experienced cognitive decline. Of these 13, nine were diagnosed with MCI and four were diagnosed with Alzheimer’s disease.

The rate of MTL atrophy—but not whole brain atrophy—was a significant predictor of cognitive decline. The MTL atrophy rate accurately predicted whether cognitive decline would occur in 89% (40 of 45) of the participants. Women and people over the age of 70 who had an increased MTL atrophy rate were at especially high risk of experiencing cognitive decline.

How Does This Affect You?

Previous studies have shown that people with MCI have more extensive MTL changes. But these findings are the first to suggest that increased rates of MTL atrophy can help predict future cognitive decline. Furthermore, this study shows that looking at the MTL region of the brain may be more informative that looking at the whole brain.

This study is not the first to suggest brain imaging may help predict cognitive and behavioral conditions. Other studies are also finding new ways to use MRI testing for diagnosing conditions and determining risk. In a new study in the November 22, 2003 issue of The Lancet , for example, researchers performed MRI scans on children with and without attention-deficit hyperactivity disorder (ADHD). They found that the children with ADHD had significant reductions in brain size and more grey matter abnormalities, compared with children without ADHD.

What does this mean for the future? MRI testing of the brain may one day become a routine part of preventive care in the elderly. Assuming the test is accurate (as it was in this study) and early action can effectively delay the onset of cognitive decline, this could be of great benefit for older adults. If the test produces too many false positive results, however, or there is no way to use the information to the advantage of the patient, MRI screening for cognitive decline could ultimately produce more harm than good.

Currently, there are no known medications or other interventions that can consistently delay the onset of cognitive decline in the near term. The recent development of several modestly effective drugs for established Alzheimer’s disease suggests that this is likely to change in the future. At that point, MRI screening could become a useful means to determine which patients should be treated before they develop symptoms. Until then, predicting cognitive decline based on MRI scanning is best left to researchers.