ArticlesPrevalence and severity of cognitive impairment with and without dementia in an elderly population
Introduction
The development of strategies to prevent or delay the onset of dementia1, 2, 3, 4, 5, 6, 7 has drawn new attention to the problem of mild cognitive impairment in the elderly.8 The writing committee of the Lancet conference on dementias characterised the description and measurement of “cognitive impairment, no dementia” (CIND) as one of the most important challenges in dementia epidemiology,9 and Bowen and colleagues8 have highlighted the importance of isolated memory loss as a risk of dementia. We report the first comprehensive estimate of CIND in an elderly population. We describe the prevalence and severity of CIND and dementia, analyse differences between mild dementia and CIND, and address the relative burden, in terms of institutional care of elderly people, of CIND and the dementias.
Section snippets
Methods
The Canadian Study of Health and Aging is a multicentre study of the epidemiology of cognitive impairment involving a representative population sample of 10 263 Canadians aged 65 and older.10, 11, 12 All individuals in the community sample who were found to be positive for cognitive impairment on the modified mini-mental state examination (score < 78) were invited for clinical examination; a randomly selected sample who were negative for impairment on screening were also invited. Consenting
Results
Table 2 shows the combined community and institutional prevalence of cognitive impairment by severity, sex, and age-group. Among Canadians aged 65 and older, 75.2% were estimated not to be cognitively impaired. The prevalence of CIND was 16.8%, which was more than all types of dementia combined (8.0%). The prevalence of all types of cognitive impairment, including CIND and the dementias, increased with age and affected 65% of those aged 85 and older.
Table 3 gives, for each diagnostic category,
Discussion
Our data are consistent with earlier reports of the prevalence of dementia in the elderly10, 20 and characteristics of patients with CIND.12 The data suggest that although the dementias are the form of cognitive impairment in the elderly causing the greatest burden, they are not the most common. Two-thirds of the elderly population with clinically definable cognitive impairment did not have dementia. Circumscribed memory impairment was the most common category of cognitive impairment,
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