Objectives and Methods:The purpose of this study was to examine the incidence of mild cognitive impairment (MCI) and patterns of progression from incident MCI to dementia in 285 cognitively normal subjects (mean age, 78.9 years) in the Cardiovascular Health Study-Cognition Study from 1998-1999 to 2010-2011. Results: Two hundred (70%) of the participants progressed to MCI; the age-adjusted incidence of MCI was 111.09 (95% confidence interval, 88.13-142.95) per 1,000 person-years. A total of 107 (53.5%) of the incident MCI subjects progressed to dementia. The mean time from MCI to dementia was 2.8 Ϯ 1.8 years. Forty (20%) of the incident MCI cases had an "unstable" course: 19 (9.5%) converted to MCI and later returned to normal; 10 (5%) converted to MCI, to normal, and later back to MCI; 7 (3.5%) converted to MCI, to normal, to MCI, and later to dementia; and 4 (2%) converted to MCI, to normal, and later to dementia. There was an increased mortality rate among the cognitively normal group (110.10 per 1,000 person-years) compared to those with incident MCI who converted to dementia (41.32 per 1,000 person-years).
Conclusions:The majority of the subjects aged Ͼ80 years developed an MCI syndrome, and half of them progressed to dementia. Once the MCI syndrome was present, the symptoms of dementia appeared within 2 to 3 years. Progression from normal to MCI or from normal to MCI to dementia is not always linear; subjects who developed MCI and later returned to normal can subsequently progress to dementia. Competing mortality and morbidity influence the study of incident MCI and dementia in population cohorts. Neurology Older persons with mild cognitive impairment (MCI) have an increased risk of developing dementia, especially Alzheimer disease (AD).1-4 The prevalence rates of MCI range from 3% to more than 20%, depending on the classification methods (e.g., amnestic vs multiple cognitive domain), 5,6 and although there are extensive data on the incidence of dementia in subjects with MCI, there are few data on the incidence of MCI in cognitively normal subjects. 3,[7][8][9][10][11][12][13][14][15][16] The existing data show an incidence in the range of 37 to 77 per 1,000 person-years (py). Individuals with MCI progress to dementia at a rate of 5% to 15% per year, 1,4 although as many as 40% to 50% of the subjects can return to cognitive normality (normal) 3,9 ; thus, the natural history of MCI could be very unstable. If so, this makes the determination of its incidence a challenge, because individuals who have normal cognition at one point in time may