Epidemiology of clinically diagnosed Alzheimer's disease.

This report reviews the current status of descriptive and analytic epidemiology of clinically diagnosed Alzheimer's disease (AD). Since AD can be diagnosed with certainty only at autopsy, currently available epidemiological data are based on a presumed clinical diagnosis. Current data indicate that AD represents a major health problem, at least in the developed countries. The prevalence ratio for AD ranges between 1.9 and 5.8 cases per 100 population aged 65 and over. Moreover, its prevalence is likely to increase in the next twenty years as a consequence of current demographic trends. The prevalence ratio for AD increases steeply with age and is higher in females. Incidence rates show a similar pattern, suggesting that AD should not be subdivided in a presenile and a senile form based on age of onset alone. Annual incidence rates of 2.4 cases per 100,000 population between ages 40 and 60, and 127 cases per 100,000 population after age 60 have been reported. Several case-control studies show that the occurrence of either dementia or Down's syndrome in other family members, advanced age of the mother at subject's birth, and head injury are possible risk factors.