Letters to the editor

Community-based studies of survival in dementia The recent article (1) on the Leiden study provides an interesting addition to the small number of studies of survival in dementia. However, the author’s statement that only 3 community-based studies of survival in dementia have been reported cannot go unchallenged. Five recent studies (2-6) have investigated community samples of reasonable size and presented results on mortality in dementia or cognitive impairment in comparable terms and have given surprisingly similar results, even though they used different definitions of dementia or cognitive impairment. Three of these were based in the United Kingdom. An urban sample 65 and over (3) found a mortality risk of 4.39 (odds ratio; 95% confidence interval (CI) 2.29 to 8.05) for AGECAT dementia syndrome relative to mentally healthy people. A rural sample 65 and over (4)found a relative risk of 3.50 (95% CI 2.37 to 5.17) for those scoring I8 on the MSQ relative to 9 or 10. A semi-rural sample 75 and over ( 5 ) found a hazard ratio of 4.18 (95% CI 2.73 to 6.41) for those scoring I 7 on CAPE IjO scale relative to 12. The other 2 studies were an urban study in the United States (2) that concentrated on the old-old (aged 75 and over), quoting a rate ratio of 3.0 (95% CI 2.1 to 3.1) for DSM-I11 dementia relative to the remainder of the cohort. The odds ratio can be computed from the table as 3.08 (95% CI 1.86 to 5.10). Despite a higher level of vascular dementia, the Beijing study (6) gives a standardized mortality rate of 2.95 (no CI quoted), comparable to the figures given above. It is interesting that the mortality rate ratio found by the Leiden group, 1.9 (95% CI 1.7 to 2.2), is much lower than these other figures, and it may be that this is a feature of their older sample. Their finding that severity of dementia is unrelated to survival agrees with one of the studies (4), although it is at variance with the 2 other studies that have reported on this (3, 5). Further studies are clearly needed to resolve this issue. The use of a 2-stage design in which those negative at initial screening were not followed up may have meant that some cases of dementia were contained within the non-demented group. This may

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mean a slight underestimation of the risk. However, their design is clearly superior to those that just use a measure of cognitive impairment (4, 5 ) rather than diagnosed dementia. References 1. HEERENTJ, VAN HEMERTAM, ROOYMANS HGM. A community-based study of survival in dementia. Acta Psychiatr Scand 1992: 85: 415-418. 2. ARONSON MK, 001WL, GEVADL, MASURD, BLAUA, W. Dementia: age dependent incidence, prevaFRISHMAN lence, and mortality in the old old. Arch Intern Med 1991: 151: 989-992. 3. DAVIDSON IA, DEWEY ME, COPELAND JRM. The relationship between mortality and mental disorder: evidence from the Liverpool longitudinal study. Int J Geriatr Psychiatry 1988: 3: 95-98. JAG, RESTALL DB, RAWLINSON F, 4. EAGLESJM, BEATTIE HAGENS, ASHCROFT GW. Relation between cognitive impairment and early death in the elderly. Br Med J 1990: 300: 239-240. M. Mortality risks in the elderly: five5. JACGERC, CLARKE year follow-up of a total population. Int J Epidemiol 1988: 17: 111-114. 6 . Lr G, SHENYC, CHENCH, ZHAUYW, LI SR, Lu M. A three-year follow-up study of age-related dementia in an urban area of Beijing. Acta Psychiatr Scand 1991: 83: 99-104.

Michael E. Dewey University Department of Psychiatry University of Liverpool P.O. Box 147 Liverpool L69 3BX United Kingdom Reply

We would like to thank Mr Dewey for his comment on our article (1). We understand that the omission of 5 studies in an article in which only 3 other studies are referred to cannot go unchallenged. Naturally, this cannot go unchallenged by us. Three of the studies (2-4) mentioned by Dewey were known to us and excluded for various reasons. Two of these (2, 3) were excluded because they only reported about survival in patients with cognitive impairment as measured with a short questionnaire comparable to the Mini-Mental State Examination we used in the

Community-based studies of survival in dementia.

Letters to the editor Community-based studies of survival in dementia The recent article (1) on the Leiden study provides an interesting addition to...
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