Location, location, location: Placement of pathology may matter more than type
Two reports in the May Archives of Neurology suggest the specific type of pathology under way in the brain may be less important in determining symptoms than where the problem occurs. Problems affecting memory regions will cause memory symptoms.
Brain autopsies of older adults enrolled in the Mayo Clinic Alzheimer Disease Patient Registry show that few of those diagnosed with amnestic (memory-focused) mild cognitive impairment (MCI) had sufficient levels of pathology to meet criteria for Alzheimer's disease. However, all had some type of abnormality affecting key memory regions, and most seemed to be on the road toward meeting standards for Alzheimer's in the future. Most also had evidence of other abnormalities in addition to the "classic" plaques and tangles of Alzheimer's, suggesting "pure" Alzheimer's disease may be relatively uncommon.
The researchers also studied registrants who progressed from having memory-focused MCI to a diagnosis of dementia. These autopsies showed that while about 70 percent met criteria for Alzheimer's disease, 82 percent had two or more processes contributing to their dementia symptoms. Again, a key feature seemed to be pathology of any kind in areas important in memory.
"These findings make an important addition to our limited data on how brain pathology relates to MCI and how MCI progresses to dementia," says William H. Thies, Ph.D., Alzheimer's Association vice president, medical and scientific relations. "However, autopsy studies will never completely meet our need for this information, because of the inevitable time lag between the last cognitive evaluation and time of death. We need to continue our work toward developing imaging methods, blood tests, or other strategies that tell us exactly what's going on in the brain while people are still alive."
Ronald C. Petersen, M.D., Ph.D., an author of both reports, serves as vice-chair of the Alzheimer's Association Medical and Scientific Advisory Council. He is also a co-principal investigator of the Alzheimer's Disease Neuroimaging Initiative (ADNI), a new $60 million nationwide study aiming to establish standard protocols for brain imaging and other laboratory tests that may provide a better basis for diagnosing Alzheimer's, tracking progression, and monitoring response to next-generation drugs. Widely regarded as a giant step toward deeper understanding of the living brain, ADNI is currently seeking volunteers with MCI, mild Alzheimer's disease, and no cognitive impairment.
