Cognitive Impairment without Dementia in Older Adults

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The summary below is from the full report titled "Prevalence of Cognitive Impairment without Dementia in the United States." It is in the 18 March 2008 issue of Annals of Internal Medicine (volume 148, pages 427-434). The authors are B.L. Plassman, K.M. Langa, G.G. Fisher, S.G. Heeringa, D.R. Weir, M.B. Ofstedal, J.R. Burke, M.D. Hurd, G.G. Potter, W.L. Rodgers, D.C. Steffens, J.J. McArdle, R.J. Willis, and R.B. Wallace.

What is the problem and what is known about it so far?

Dementia is a condition that affects memory and thinking enough to interfere with normal daily activities. About 3.5 million Americans age 71 years or older have dementia. Some older people may have mild cognitive problems without meeting criteria for dementia. Mild cognitive impairment might affect attention, language, judgment, memory, reading, or writing. It may be noticeable to the individual or to other people, but it does not severely impair activities of daily living. Few studies examine the frequency and course of mild cognitive impairment in older adults.

Why did the researchers do this particular study?

To estimate the frequency of mild cognitive impairment among older adults in the United States.

Who was studied?

A group of 856 people age 71 years and older who were participating in the national Health and Retirement Study.

How was the study done?

The researchers sampled a group of older people who were participating in a large national study, the Health and Retirement Study. They asked proxies (usually a spouse or adult child) to describe the older person's symptoms and medical history. They also examined the older person and administered many neuropsychological tests. They used all of the information to diagnose dementia, cognitive impairment without dementia, or normal cognition. They then applied the estimates of the frequency of cognitive impairment without dementia that were derived from the sample to the 2002 population of older people in the United States. Finally, the researchers questioned the proxies of some of the older persons 16 to 18 months later to assess outcomes, such as death or progression to dementia.

What did the researchers find?

About 22% of the older people had cognitive impairment that did not reach the threshold for dementia. Applied to people age 71 years or older in the United States in 2002, 5.4 million older people had cognitive impairment without dementia. Annually, about 8% of those who had cognitive impairment without dementia died and about 12% progressed to dementia.

What were the limitations of the study?

Criteria that distinguish mild cognitive impairment from dementia are imperfect. Only about one half of the sampled older persons completed their initial assessments.

What are the implications of the study?

Cognitive impairment without dementia probably affects a large segment of the elderly population.