ORIGINAL ARTICLE: Prevalence and predominance of Alzheimer type dementia in rural Japan

Background:The aim of the present study was to estimate prevalence rates of dementia and its subtypes in the population aged 65 years or more in a rural area of Japan. Methods:A survey was conducted in Itoigawa, a city with 33 120 inhabitants in Niigata Prefecture, Japan. There were 7847 persons aged 65 years or older, and they comprised 23.4% of the total population. The first phase survey included questions on medical history, activities of daily living, psychiatric and behavioral symptoms and MMSE. When the responses were examined 6394 valid replies were received (81.5%) and 914 subjects were identified who were suspected of having dementia. In addition, 200 samples were selected randomly as controls from the 5480 people who were not suspected of dementia. The second phase survey was applied to a total of 1114 subjects. Pairs of psychiatrists and nurses made house-to-house visits and examined the subjects in detail. Clinical diagnoses of the subtypes of dementia were based on the criteria set out by the Consortium to Establish a Registry for Alzheimer's Disease and DSM IV. Results:The prevalence rate of dementia was estimated at 6.2% (men 4.5%, women 7.4%), which is higher than that found by previous reports in Japan. Alzheimer type dementia was the most frequent diagnosis, accounting for 4.0%, followed by vascular dementia (1.2%), other type of dementia (0.3%) and unknown dementia (0.8%). 'Questionable dementia', as defined by the Clinical Dementia Rating 0.5, was found in 4.4% of respondents (men 6.3%, women 3.0%). Conclusions:The prevalence of dementia in a rural area was higher than that of previous Japanese reports, and the prevalence rate of Alzheimer type dementia was much higher than that of vascular dementia.