Prevalence of clinically diagnosed Alzheimer's disease and other dementing disorders

The purpose of this study was to investigate the prevalence of dementia in an Italian population using a door-to-door 2-phase design. As part of a social and health survey, we administered the Hodkinson abbreviated mental test to all persons over age 59 residing in the Commune of Appignano on January 1, 1987 (N = 778). We then investigated all subjects scoring 7 or less on the cognitive test following a standardized diagnostic protocol. We found 48 patients affected by dementia, yielding a crude prevalence ratio (cases per 100 population over age 59) of 6.2; prevalence ratios were 2.6 for Alzheimer's disease, 2.2 for multi-infarct dementia, 0.8 for mixed dementia, 0.4 for secondary dementia, and 0.3 for unspecified dementia. Age- and sex-specific prevalence ratios increased steeply with age and were consistently higher in women for Alzheimer's disease and in men for dementia of all types and multi-infarct dementia. Alzheimer's disease was slightly more frequent than multi-infarct dementia; however, the most common type of dementia varied across age groups. Most cases of Alzheimer's disease were sporadic and had a late age of onset. Comparison with other populations suggests that dementia of all types is as frequent in Appignano as elsewhere, and that Alzheimer's disease might be more frequent in rural than in urban populations.