Elsevier

The Lancet

Volume 349, Issue 9068, 21 June 1997, Pages 1793-1796
The Lancet

Articles
Prevalence and severity of cognitive impairment with and without dementia in an elderly population

https://doi.org/10.1016/S0140-6736(97)01007-6Get rights and content

Summary

Background

Not all cognitively impaired people have dementia, but those who do not meet current criteria for dementia have received little study. We report a comprehensive estimate of the prevalence of “cognitive impairment, no dementia” (CIND) in an elderly population.

Methods

The Canadian Study of Health and Aging gathered population representation information about elderly Canadians aged 65 and over from 36 cities and surrounding areas in five regions. In each region, the sample size was 1800 people in the community and 250 people in institutions. Patients in the community were screened for cognitive impairment by means of the modified mini-mental state examination. Those who scored below the cut-off point (n=1106) and a randomly selected sample of those who scored above the cut-off point (n=494) were referred for clinical examination. 59 individuals unable to take the screening test were also assessed clinically. We selected 17 long-term care institutions in each region, and then randomly selected consenting residents of these institutions for clinical assessment (n=1255).

Results

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 dementias, increased with age. Patients with CIND were three times more likely to be living in institutions than were cognitively unimpaired patients (odds ratio 3.1 [95% CI 2.4–3.9]). Circumscribed memory loss has a prevalence of 5.3% in the elderly Canadian population, and was the most common category. CIND was related to some degree of functional impairment in elderly patients.

Interpretation

CIND is commonly associated with functional disability and a need for institutional care. This diagnostic category includes a costly group of disorders that merit further study.

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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