P1–178: Incidence of dementia and dementing diseases in Japan: The Osaki–Tajiri project (1)

Prevalence studies on dementia have been performed in many areas, however, an incidence of dementia has not been fully investigated due to practical difficulties. We previously performed the dementia prevalence study in 1998 and reported that the prevalence was 8.5% in the town of Tajiri (Miyagi Prefecture, northern Japan). The most common dementing condition was found to be Alzheimer's disease (AD) with cerebrovascular diseases (CVD). We performed a dementia incidence study 5–7 years after the survey to investigate an incidence of dementia and the risk factors. We targeted 525 participants aged 65 years or older who were previously assessed as the Clinical Dementia Rating (CDR) 0 (healthy) or 0.5 (questionable dementia) in the 1998 survey. Finally, 414 older adults agreed to participate. 1) Healthy at baseline: 223 older adults who were previously evaluated as the CDR 0 were re–assessed 5 years after the prevalence study. 2) Questionable dementia at baseline: 191 older adults who were previously assessed as CDR 0.5 were also re–assessed 5–7 years after the baseline survey. All participants were assessed for the CDR and MMSE, and 217 participants were evaluated for MRI findings. Dementia was diagnosed by DSM–IIIR. AD and vascular dementia (VaD) were diagnosed by NINCDS–ADRDA and NINDS–AIREN, respectively. Informed consent was received from all the family members. Overall, 3.6% of the healthy group and 25.1% of the questionable dementia group progressed to dementia. 30 dementia patients received MRI for the diagnosis of dementing diseases: 46% of them had AD, 17% had AD with CVD, and 16% had VaD. Logistic regression analyses disclosed that older age, CDR sum of boxes, lower MMSE score, atrophic changes at baseline were significantly (p<0.05) predicted to further decline to dementia. No significant correlations were noted for lifestyle, past medical histories, and the previous psychosocial intervention. This is the first, community–based MRI study on an incidence of dementia in Japan. For the correlations with life style–related diseases, a longitudinal study from midlife would be needed.