A study of patients with mild cognitive impairment revealed that results from cognitive tests and brain scan PET can work as an early warning system for Alzheimer's disease development, according to a presentation July 14 at the Alzheimer's Association International Conference on Alzheimer's Disease (ICAD) in Vienna.
University of California (UC), Berkeley researchers found that among 85 participants with mild cognitive impairment in the study, those with low scores on a memory recall test and low glucose metabolism in particular brain region--as detected by PET--had a 15-fold greater risk of developing Alzheimer's disease within two years, compared with the others in the study.
"Not all people with mild cognitive impairment go on to develop Alzheimer's, so it would be extremely useful to be able to identify those who are at greater risk of converting [to Alzheimer's disease] using a clinical test or biological measurement," said Susan Landau, PhD, a post-doctoral fellow at UC Berkeley's Helen Wills Neuroscience Institute and the Lawrence Berkeley National Laboratory and the study's lead author.
"The field, in general, is moving toward ways to select people during earlier stages of Alzheimer's disease, including those who show no outward signs of cognitive impairment," said the study's principal investigator William Jagust, MD, a faculty member at UC Berkeley's Helen Wills Neuroscience Institute. "By the time a patient is diagnosed with Alzheimer's disease, there is usually little one can do to stop or reverse the decline. Researchers are trying to determine whether treating patients before severe symptoms appear will be more effective, and that requires better diagnostic tools than what is currently available."
In the study, researchers compared a variety of measurements that had previously shown promise as early detectors of Alzheimer's. The measurements included scores on the Auditory Verbal Learning Test; the volume of the hippocampus, the part of the brain associated with the formation of new memory; the presence of the apolipoprotein E4 gene, which has been linked to increased risk of Alzheimer's; certain proteins found in the cerebrospinal fluid; and glucose metabolism detected in PET brain scans. A low rate of glucose metabolism in a particular brain region is considered a sign of poor neural function, most likely due to the loss of synapses in that area, they said.
"What's really novel about our study is that we evaluated all of these biomarkers in the same subjects, so we could more easily compare the predictive value of any one measure over the others," Landau said. "The Auditory-Verbal Learning Test, which measures memory recall ability, and the PET scans measuring glucose metabolism were the two markers that clearly stood out over the others."
The researchers pointed out that other measurements--in particular, hippocampus volume and the cerebrospinal fluid markers--also showed promise in predicting disease progression. However, when considering all the measurements together, PET scans and memory recall ability were the most consistent predictors.
The researchers expected to have more complete information about which measures serve as the best predictors in a year as they continue to gather data for this ongoing study.
An earlier study led by Jagust found that PET scans and MRI could detect neurological changes in asymptomatic people who subsequently developed dementia or mental impairment, although it was too soon to say if those people would go on to develop Alzheimer's.
The research is part of the Alzheimer's Disease Neuroimaging Initiative, a 60-center study funded by the National Institute on Aging. The goal of the initiative is to find a biomarker for Alzheimer's that would predict individuals who will later develop Alzheimer's disease.