CANADIAN PROJECTIONS OF CASES SUFFERING FROM ALZHEIMERS-DISEASE AND SENILE DEMENTIA OF ALZHEIMER TYPE OVER THE PERIOD 1986-2031

Alzheimer's disease (AD) is characterized by irreversible changes in cognitive and intellectual functions, accompanied by progressive memory loss, and described by neurochemical and neuropathological impairments. The classic term Alzheimer's disease applies to presenile dementia, while all of the syndromes that share the distinctive signs of AD are known as senile dementia of the Alzheimer type (SDAT). In Canada, as in several other industrialized countries, we are seeing a rapid growth of the elderly population. The renewed interest in AD and SDAT is partly attributable to the view that the increasing percentage of sufferers will have a significant socioeconomic impact. Few attempts have been made to project the number of cases of SDAT in Canada. In assessing the prevalence of SDAT in an over 65 population, a rate of 2.5% (or 3%) is commonly applied. This rate corresponds to one half the estimated prevalence rate for all severe types of dementia, using an average of the rates arrived at by some ten studies. The authors dispute this approach: i. the assumption that 50% of dementia cases will be AD is not verified for all populations: ii, the use of a single prevalence rate for everyone over age 65 is rather uninformative; and iii, the combining of results from various sources is questionable given the possible lack of consistency in the following respects: diagnostic criteria, methods of investigation, effort made to recruit cases, and representativeness of the groups studied. In this article, prevalence rates by age group have been inferred based on two Finnish studies conducted in the 1980s on the prevalence of AD in the general population. The prevalence rates obtained were: one percent for ages 65 to 74, four percent for ages 75 to 84, and 10.5% for ages 85 and over. When these rates are applied to the projected population for the years 1986 to 2031 (Statistics Canada), the result is an estimated 73,696 cases occuring in 1986, and 215,847 cases in 2031. This procedure takes into account variation due to the age and heterogeneity of the population, and the authors consider these projections to be the most accurate assessment to date of the scope of the problem of SDAT in Canada.