From Medscape Medical News
Susan Jeffrey
September 10, 2010 — A new report finds a prevalence of mild cognitive impairment (MCI) of about 16% among elderly people free of dementia, with a higher prevalence among men than women.
The main purpose of this study was to determine the prevalence of MCI among a random sample of residents of Olmstead County, Minnesota, Ron C. Petersen, MD, PhD, from the Department of Neurology at Mayo Clinic in Rochester, Minnesota, told Medscape Medical News.
"As we suspected, there's a fair amount out there, and if you add the proportion of people with MCI to the proportion of people who already have dementia or Alzheimer's disease, you're at 25% to 30% of the population," Dr. Petersen said. "That's a huge number and it going to become increasingly large as time goes on."
Their research, part of the Mayo Clinic Study of Aging, appears in the September 7 issue of Neurology.
Earlier in the Process
The field of aging and dementia has been moving toward trying to identify patients as early as possible in the disease process in hopes of one day modifying the course of disease.
"MCI is considered an intermediate state between the cognitive changes of aging and the earliest clinical features of dementia, particularly Alzheimer's disease (AD)," they write.
There have been other epidemiologic studies of MCI, "but most investigators retrofitted the criteria for MCI to previously collected clinical information, used a variety of detection procedures, and implemented the MCI diagnostic criteria using different algorithms," Dr. Petersen and colleagues point out. "By contrast, we evaluated in person a population-based sample specifically to detect MCI and its subtypes using published diagnostic criteria."
In this analysis, they evaluated an age- and sex-stratified random sample of residents of Olmstead County who were between the ages of 70 and 89 years on October 1, 2004, using the Clinical Dementia Rating Scale, as well as neurologic and neuropsychological testing to assess 4 cognitive domains, including memory, executive function, language, and visuospatial skills.
The data generated on each individual was then reviewed by an adjudication panel and assessed as MCI, AD, or normal cognition.
Of 1969 participants assessed, 329 had MCI, for a prevalence of 16%; most cases were amnestic MCI.
Table. Prevalence of MCI in Nondemented Elderly 70 to 89 Years Old in Olmstead County
Group Prevalence, % (95% CI)
Any MCI 16.0 (14.4 – 17.5)
Amnestic MCI 11.1 (9.8 – 12.3)
Nonamnestic MCI 4.9 (4.0 – 5.8)
CI = confidence interval; MCI = mild cognitive impairment
The prevalence of MCI increased with age and, as has been previously reported by this group, was more common in men; the prevalence odds ratio for men vs women was 1.54 (95% confidence interval, 1.21 –1.96), after adjustment for age, education, and nonparticipation.
"The higher prevalence of MCI in men may suggest that women transition from normal cognition directly to dementia at a later age but more abruptly," the study authors speculate.
"Because evidence indicates that Alzheimer's disease may cause changes in the brain 1 or 2 decades before the first symptoms appear, there is intense interest in investigating MCI and the earliest stages of cognitive decline," said National Institute on Aging (NIA) Director Richard J. Hodes, MD, in a statement from the NIA that provided much of the funding. "While more research is needed, these findings indicate that we may want to investigate differences in the way men and women develop MCI, similar to the way stroke and cardiovascular disease risk factors and outcomes vary between the sexes."
The prevalence of MCI was also higher in those who reported they had never married and those with the known AD risk alleles APOE ε3ε4 or ε4ε4. The prevalence of MCI was significantly lower with increasing years of education (P for linear trend < .0001).
New Definition
At the recent Alzheimer's Association International Conference on Alzheimer's Disease (ICAD) 2010 in Honolulu, Hawaii, in July, draft reports from 3 workgroups were presented that will form the basis for new diagnostic criteria for MCI and AD — the first update of the current criteria in 25 years — as well as outlining a new category of preclinical AD.
The workgroups were convened by the NIA and the Alzheimer's Association to update criteria established by the National Institute of Neurological Disorders and Stroke/Alzheimer's Disease and Related Disorders Association — now the Alzheimer's Association — in 1984.
Dr. Petersen participated on the MCI committee, not surprising because his work largely established the concept.
"The committees are entertaining should we be looking earlier in the clinical spectrum of impairment to move the threshold for what we call Alzheimer's disease," he said. "Right now it's at the dementia stage where people are impaired in multiple cognitive areas, and they are functionally impaired."
There is a move to back a diagnosis of AD into the MCI stage, he noted, "because the sooner we pick it up, the more likely we'll be able to do something about it. But the challenge with moving it back to the MCI stage is that not everybody who's memory impaired will necessarily develop Alzheimer's disease and that's where the role of imaging and biomarkers come in that were discussed at ICAD and are the subject of further discussion and further research
"The purpose is hopefully the sooner we identify these people who are in the early stages we'll be able to do something about it in the future," he said.
The study was supported by the National Institutes of Health and the Robert H. and Clarice Smith and Abigail van Buren Alzheimer's Disease Research Program. The study was made possible by the Rochester Epidemiology Project. Dr. Petersen serves on scientific advisory boards for Elan Corporation, Wyeth, and GE Healthcare; receives royalties from the publication of Mild Cognitive Impairment (Oxford University Press), and receives research support from the National Institutes of Health/NIA. Disclosures for coauthors appear in the paper.
Neurology. 2010;75:889-897.
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