A new study by researchers in the US suggests over 5 million elderly Americans below the threshold for dementia have cognitive impairment that reduces the performance of memory, thinking and other faculties.
The study is published in the 18th March issue of the Annals of Internal Medicine and is the work of Dr Brenda Plassman, of Duke University Medical Center in Durham, North Carolina, and colleagues.
Plassman and colleagues conducted the longitudinal study because cognitive impairment, even without dementia can still increase the chances of elderly people being disabled, having higher health care costs and progressing to dementia, but there are no population based estimates of the prevalence of this condition in the US.
The study ran from July 2001 to March 2005, and involved participants taking part in ADAMS (Aging, Demographics, and Memory Study) which recruits from the nationally representative HRS (Health and Retirement Study).
The researchers selected 1,770 individuals aged 71 and over, and 856 of these went on to complete initial home based assessments.
Of the 856 who completed initial assessments, Plassman and colleagues selected 241, from which 180 completed follow up assessments 16 to 18 months later.
Using neurologic exams, neuropsychological tests, and clinical and medical history, the researchers grouped the participants according to the following diagnoses at the start of the study: normal cognition, cognitive impairment without dementia, or dementia. They estimated national prevalence rates using a population weighted sample.
The results showed that:
- For 2002, an estimated 5.4 million (22.2 per cent) of Americans aged 71 and over had cognitive impairment without dementia.
- This included 8.2 per cent with prodromal (early, non-specific) Alzheimer’s disease and 5.7 per cent with cerebrovascular disease (stroke).
- Of those who completed the follow up assessments, 11.7 per cent of participants with cognitive impairment but no dementia went on to develop dementia each year.
- For those with prodromal Alzheimer’s disease and stroke, the figure was higher, at 17 and 20 per cent respectively.
- The annual rate of death for those with cognitive impairment without dementia was 8 per cent.
- This figure rose to nearly 15 per cent for those whose cogntive impairment was due to medical conditions.
The authors concluded that:
“Cognitive impairment without dementia is more prevalent in the United States than dementia, and its subtypes vary in prevalence and outcomes.”
One possible drawback mentioned by the researchers was the fact only 56 per cent of the original selected participants who did not die completed the initial assessment.
Plassman told Reuters that she and her team were also working to find out how impaired thinking, memory and other cognitive abilities, both with and without dementia, affected American families and the health care system in the US, “so we will be able to see the true human and economic costs of these conditions,” she said, adding that:
“Hopefully this research will also lead toward developing interventions and treatments, so that cognitive impairment is not one of the leading concerns in late life when our children are in their 70s and 80s.”
“Prevalence of Cognitive Impairment without Dementia in the United States.”
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.
Ann Intern Med 2008; 427-434.
18 March 2008, Volume 148 Issue 6, Pages 427-434.
Sources: Annals of Internal Medicine press statement, journal abstract, Reuters.
Written by: Catharine Paddock