Progression of mild cognitive impairment to Alzheimer's or vascular dementia versus normative aging among elderly Chinese.

To compare differences in evolutionary progressions from Mild Cognitive Impairment (MCI) to dementia of Alzheimer's type (DAT) or to vascular dementia (VaD) versus normal aging, subjects identified as MCI or as cognitively normal (CN) during standard cognitive evaluations among a large epidemiological study designed to determine prevalence and incidence of dementia and its major subtypes in Beijing, China were re-examined after an interval of approximately 3 years, repeating the same investigation protocol as at baseline. MCI subjects meeting criteria for dementia and the two major subtypes, DAT and VaD were identified at follow-up evaluation. Annual conversion rates for combined dementias and for major subtypes of DAT and VaD, from MCI, were compared with conversion rates among CN subjects. Relative risks for conversion from MCI to major subtypes of dementia were also compared with CN subjects by Cox regression models. 175 MCI and 400 CN subjects were identified at baseline. Among 121 MCI subjects available at follow-up, 51 were diagnosed with dementia (29 with DAT, 18 with VaD and 4 with other dementias), compared with 14(10 DAT, 3 VaD and 1 other type dementia) diagnosed as dementia among 281 CN subjects available at follow-up. Annual conversion rates calculated from MCI to all dementias, compared with conversion rates from CNs, were 14.1% versus 1.6%. Specifically for DAT, annual conversion rates were 8.0% versus 1.1% and for VaD were 5.0% versus 0.3%. Relative risks for developing all dementias, DAT and VaD among MCI subjects were 9, 6 and 5 times greater than among CN subjects. Conversion rates among MCI subjects to dementia, and major subtypes, for elderly Chinese residents of Beijing were comparable with results reported among similar studies worldwide. Risks of developing dementia, and major subtypes, among MCI subjects in Beijing were significantly higher than among normal subjects. Identification of MCI among elderly populations provides the possibilities for dementia prevention and treatment within prodromal stages.