Prevalence of Widespread Cognitive Impairments in the Elderly

Abstract & Commentary

By Mary Elina Ferris, MD, Clinical Associate Professor, University of Southern California. Dr. Ferris reports no financial relationship to this field of study.

Synopsis: Cognitive impairment in the U.S. population without dementia is found in 22% of those over age 70. This is more than the number of those with Alzheimer's or other dementias alone, and needs to be recognized and addressed in our healthcare of this group.

Source: Plassman BL, et al. Prevalence of cognitive impairment without dementia in the United States. Ann Intern Med. 2008;148:427-434.

This large population study of U.S. participants born before 1954 began in 1992 to investigate health, social, and economic implications of aging, collecting data from a sample of 22,000. A subset of 1770 individuals age 70 or older was identified to determine the national prevalence of dementia and other cognitive impairments, titled ADAMS (Aging, Demographics, and Memory Study). Participants were assessed by nurses and psychiatric technicians at their residence, and they completed a battery of neuropsychological measures. Blood pressure, lab testing and videotapes were also collected. Since self-reporting of these issues can be unreliable, proxies (usually spouses or adult children) also provided information. All this data was then analyzed by an expert consensus panel to determine the diagnosis in 2 stages, both with and without the medical records. In the majority of cases the diagnosis did not change with the addition of medical records.

ADAMS participants were divided within 3 general categories: normal cognitive function, dementia, and cognitive impairment without dementia. The latter is defined as mild cognitive or functional impairment that does not meet criteria for dementia, or performance on neuropsychological measures that was at least 1.5 standard deviations below published norms.

For the age group 71-79 years, 16% were found to have cognitive impairment without dementia, and 6% with prodromal Alzheimer's disease; this increased to 29% and 10% for the age group 80-89 years. At 90 years old and above, the prevalence for cognitive impairment without dementia was 40%, and 22% had prodromal Alzheimer's disease.

Of the 856 who completed initial assessments, 241 were selected for follow-up, and 180 completed a 16- to 18-month follow-up assessment. An annualized rate of 12% for progression to dementia was found, with a higher rate of 17-20% for prodromal Alzheimer and stroke groups. Of those who did progress to dementia, 83% had a diagnosis of Alzheimer disease and 17% had vascular dementia.

Commentary

Based on the prevalence identified in this population study, the authors estimate that 22% (or 5.4 million individuals) of the U.S. population over age 70 have cognitive impairment without dementia. They further extrapolate a predicted progression to dementia of 12% per year, higher in those identified with a prodrome of Alzheimer's disease. By age 90 and above, fully 40% have cognitive impairment without dementia, and 22% have a prodrome of Alzheimer's disease.

These new figures are 70% higher than previous findings of frank dementia alone in 14% of this same population group.1 Again, the numbers increase with age, from 5% of those aged 71-79 years, to 37% of those aged 90 and older having dementia. This data helps us understand the amount of impairment we can expect in our elderly patients, even before obvious dementia develops, and enables us to provide more evidence-based advice for families on what to expect when their elderly relatives exhibit early signs of cognitive impairments.

Reference

1. Plassman BL, et al. Prevalence of dementia in the United States: the aging, demographics, and memory study. Neuroepidemiology. 2007;29:125-132.