Mohammed T. Abou-Saleh

DEMENTIA EPIDEMIOLOGY: PREVALENCE AND INCIDENCE 19790 years, with no sign of levelling off. The incidence of vasculardementia showed similar trends, but the actual rates varied greatlyfrom study to study. There was no sex difference in dementia, butwomen tended to have a higher incidence of Alzheimer’s disease invery old age, and men a higher incidence of vascular dementia atyounger ages. There were also regional differences, with EastAsian countries having a significantly lower incidence of dementiathan Europe, and also tending to have a lower incidence ofAlzheimer’s disease. Tables 38.3 and 38.4 summarize the resultsfor different regions and levels of severity.The second meta-analysis, by Gao et al. 12 , involved only thesubset of 12 studies that used DSM-III criteria for dementia andNINCDS–ADRDA criteria for Alzheimer’s disease. The datawere fitted with a logistic model and a levelling of the rate ofincrease with age was found. Women were found to have a higherincidence of Alzheimer’s disease than men. The estimatedincidence rates are also shown in Tables 38.3 and 38.4. It can beseen that the rates of Gao et al. 12 are different from those of Jormand Jolley 11 and the two meta-analyses came to differentconclusions about whether there is a levelling in the rise withage. The difference arises because Gao et al. 12 pooled data fromdifferent regions and different levels of severity. Their rates fall inbetween those of Jorm and Jolley 11 for Mild+ and Moderate+dementia. Deviations from an exponential rise can result if thestudies contributing cases at the upper ages are examining milderdementia or are from regions with a lower incidence.CONCLUSIONSThe prevalence and incidence of dementia rise exponentially withage up to age 90. There is no consensus about what happens atextreme ages, because of the limited data available, but somelevelling in the rise is a possibility. Women probably have a higherprevalence and incidence of Alzheimer’s disease. Conversely, menmay be at greater risk of vascular dementia. There appear to beimportant regional differences, although the proper investigationof these requires studies with identical methodologies in thevarious sites.REFERENCES1. Erkinjuntti, T, Østbye T, Steenhuis R, Hachinski V. The effect ofdifferent diagnostic criteria on the prevalence of dementia. N Engl JMed 1997; 337: 1667–74.2. Jorm AF, Korten AE, Henderson AS. The prevalence of dementia: aquantitative integration of the literature. Acta Psychiat Scand 1987;76: 465–79.3. Dewey ME. How should prevalence be modelled? Acta PsychiatScand 1991; 84: 246–9.4. Hofman A, Rocca WA, Brayne C et al. The prevalence of dementia inEurope: a collaborative study of 1980–1990 findings. Int J Epidemiol1991; 20: 736–48.5. Ritchie K, Kildea D. Is senile dementia ‘‘age-related’’ or ‘‘ageingrelated’’?—evidencefrom meta-analysis of dementia prevalence in theoldest old. Lancet 1995; 346: 931–4.6. Ritchie K, Kildea D, Robine J-M. The relationship between age andthe prevalence of senile dementia: a meta-analysis of recent data. Int JEpidemiol 1992; 21: 763–9.7. McGee MA, Brayne C. The impact on prevalence of dementia in theoldest age groups of differential mortality patterns: a deterministicapproach. Int J Epidemiol 1998; 27: 87–90.8. Rocca WA, Hofman A, Brayne C et al. Frequency and distribution ofAlzheimer’s disease in Europe: a collaborative study of 1980–1990prevalence findings. Ann Neurol 1991; 30: 381–90.9. Corrada M, Brookmeyer R, Kawas C. Sources of variability inprevalence rates of Alzheimer’s disease. Int J Epidemiol 1995; 24:1000–1005.10. US General Accounting Office. Alzheimer’s Disease: Estimates ofPrevalence in the United States. Washington, DC: United StatesGeneral Accounting Office.11. Jorm AF, Jolley D. The incidence of dementia: a meta-analysis.Neurology 1998; 51: 728–33.12. Gao S, Hendrie HC, Hall KS, Hui S. The relationships between age,sex, and the incidence of dementia: a meta-analysis. Arch GenPsychiat 1998; 55: 809–15.