Prognosis of vascular mild cognitive impairment includes vascular dementia onset and death by cardiovascular disease: reanalysis from the Osaki-Tajiri project.

The relationship of predementia stage with cerebrovascular disease (CVD) has not been fully clarified. Following our Prevalence Study 1998 in Tajiri, Japan, Incidence Study 2003 disclosed that 17.9% of subjects developed vascular dementia (VaD). Some cases developed after stroke (type I), whereas others already met the criteria for subcortical VaD (SVD) despite very mild stage (Clinical Dementia Rating [CDR] 0.5) and progressed to mild stage (CDR 1) (type II). We hypothesized that prognosis of vascular mild cognitive impairment (MCI) included type II VaD or death due to causes associated with vascular risk factors. Prevalence Study 1998 included 497 randomly selected participants, including 346 with a CDR of 0, 119 with a CDR of 0.5, and 32 with a CDR of 1+. The first 2 groups were targeted for Incidence Study 2003. Based on the database, we reanalyzed the ratio of SVD in the subjects with CDR 0.5 and VaD, prognosis with or without CVD, and 2 types of VaD onset. The criteria for SVD were achieved by 67% of those with VaD and by 7% of those with vascular MCI (ie, CDR 0.5). In the CDR 0 group, CVD had no affect on prognosis; however, in the CDR 0.5 group, CVD had an affect on death by cardiovascular disease. The majority of subjects in the CDR 0 and CDR 0.5-CVD (-) groups were classified as type I, whereas all subjects in the CDR 0.5-CVD (+) group were type II. Although vascular MCI is treatable, it may progress to death as well as apparent dementia. Individuals with this "buried under the community" phenomenon of SVD should be targeted for secondary prevention interventions.