Prevalence of senile dementia in a rural community in Japan: the Tajiri project.

Knowledge of the prevalence of dementia in different age groups is needed for the planning of a health policy. This study shows the prevalence of dementia and magnetic resonance imaging (MRI) findings in elderly people aged 65 years and over, living in the town of Tajiri in the northern part of Japan. They were shown by two cognitive screening tests, the Mini-Mental State examination (MMS) and the Dementia Screening Test (DST) and medical diagnosis. Two subject groups were assessed, those who completed both tests (Subjects I, n=2066) and those from among the 200 'MRI-administered subjects' who were interviewed and diagnosed (Subjects II, n=170). For Subjects I, there were 6.3 and 10.2% 'dementia range' according to the severe and mild criteria, respectively. As for Subjects II, 9.4% were clinically diagnosed as having dementia. They met the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA) criteria of probable Alzheimer's disease (AD) or possible AD with cerebrovascular disease. The estimated prevalence rate of dementia was 8.0%. Visual ratings of brain atrophy using MRI disclosed two distribution patterns. The 'continuous' pattern of the frontal and temporal lobes atrophy suggest that both are affected by the aging process, while a 'discontinuous' pattern of the hippocampal atrophy could indicate a pathologic background such as early changes of AD.