[Prevalence of dementia and its subtypes in a rural area in Japan].

The prevalence of dementia in Japan in 1985 for people aged 65 years or older was 4.8%. Vascular dementia (VD) has been reported to be the commonest subtype A report from Tokyo in 1970 showed that it was 2.8 times more frequent than Alzheimer type dementia (SDAT). We assessed the prevalence of dementia in a rural area (population: 12,931, 25.3% were 65 years or older in 1994) in Kyoko. First, we questioned subjects about their demographic circumstances, memory disturbance, apraxia (agnosia) and daily activities. Our questionnaire was answered by 3.132 (95.8%) subjects, and 2,280 of them agreed to be examined by neurologists. Those who met the appropriate criteria of the DSM-III-R and NINCDS-ADRDA were diagnosed with dementia. By use of the Hachinski ischemic score (HIS), we distinguished VD from non-vascular dementia. In this study patients with non-vascular dementia were diagnosed with SDAT by the neurologists. Analysis of the data revealed that 4.8% of the study population was demented. According to the HIS results, only 3 of 15 had vascular dementia. The prevalence of dementia was the same as the average prevalence in Japan even though the elderly population of this town was twice as high as the average. It is hard to determine the prevalence of dementia in any community. Many factors must be taken into consideration: the coverage rate, the criteria for dementia, and whether to include institutionalized residents. The prevalence of dementia will increase with the aging of the population, and we must collect accurate data in order to plan efficiently.