Post-Mortem Brain Studies Reveal Features of Mild Cognitive Impairment

Newswise — The brains of patients with mild cognitive impairment display pathologic features that appear to place them at an intermediate stage between normal aging and Alzheimer's disease, although some patients with mild cognitive impairment develop other types of dementia, according to two studies in the May issue of Archives of Neurology, one of the JAMA/Archives journals.

Mild cognitive impairment—difficulty with thinking, learning and memory—is increasingly recognized as a neurologic transition stage between normal cognitive function and Alzheimer's disease, according to background information in both articles. Older adults with mild cognitive impairment, especially those with a variety known as amnestic (memory-related) mild cognitive impairment, are thought to have a higher risk of progressing to clinical Alzheimer's disease. Little is known about how this condition affects the physical structures of the brain.

In the first study, Ronald C. Petersen, Ph.D., M.D., Mayo Clinic College of Medicine, Rochester, Minn., and colleagues compared the findings in autopsy tissue of brains of 15 individuals who at the time of their death had amnestic mild cognitive impairment (average age 88.9 years) to those of 28 individuals who were clinically healthy at the time of their death and 23 patients who were believed to have Alzheimer's disease at death and had undergone autopsy. The patients with mild cognitive impairment were examined every year before their death, which occurred between Sept. 1, 1986, and Dec. 31, 2004.

Most of the patients did not meet the requirements for a post-death diagnosis of Alzheimer's disease. However, the changes to their brains as compared to those of individuals without cognitive difficulties were more similar to those of patients with Alzheimer's disease. For instance, the patients had begun developing neurofibrillary tangles, or tangles in the cell bodies of neurons. The number of tangles correlated with the severity of the patient's symptoms at the last examination before death. The number of brain plaques, a hallmark of Alzheimer's disease, were similar in healthy patients and patients with mild cognitive impairment, indicating that the transition to Alzheimer's disease"related dementia may occur when these plaques form in more brain areas. All patients with mild cognitive impairment had abnormalities in their temporal lobes, which likely caused their cognitive difficulties, and many also had abnormalities in other areas that did not relate to the features of Alzheimer's disease.

"The neuropathologic features of amnestic mild cognitive impairment matched the clinical features and seemed to be intermediate between the neurofibrillary changes of aging and the pathologic features of very early Alzheimer's disease," the authors conclude. (Arch Neurol. 2006;63:665-672. Available pre-embargo to the media at http://www.jamamedia.org)

Editor's Note: This work was funded by the National Institute on Aging, a grant from the Mayo Alzheimer's Disease Patient Registry, and a grant from the Mayo Alzheimer's Disease Research Center and the Robert H. and Clarice Smith and Abigail van Buren Alzheimer's Disease Research Program.