Incidence rate of mild cognitive impairment and the conversion rates into dementia or Alzheimer disease among elderly people: A population-based cohort study / 中国组织工程研究

ABSTRACT

BACKGROUND: Mild cognitive impairment (MCI) in elderly people is becoming increasingly a new hot spot for the clinical study of Alzheimer disease at present, and it is still unknown how many cases of MCI will convert into Alzheimer disease. OBJECTIVE: To analyze the incidence rate of mild cognitive impairment and the conversion rates into dementia and Alzheimer disease among elderly people.DESIGN: A prospective cohort study based on diagnosis. SETTING: Second Department of Cadre's Ward, Bethune International Peace Hospital of Chinese PLA.PARTICIPANTS: The subjects were 216 MCI patients and 2 302 subjects with normal cognition selected in the baseline investigation to the retired cadres aged 60 years and above, in 26 military cadres' sanatoriums of Shijiazhuang city between August and September 2001.METHODS: The MCI diagnosis was according to the MCI diagnostic standard in Diagnostic and Statistical Manual of Mental Disorders - Fourth Edition (DSM-Ⅳ), and the diagnosis of dementia was according to the standard in DSM-Ⅳ revised by American Psychiatric Association. Alzheimer disease was diagnosed according to the standards of National Institute of Neurological and Communicative Disorders and Stroke/the Alzheimer Disease and Related Disorders Association (NINCDS-ADRDA). All the 216 MCIpatients and 2 302 subjects with normal cognition were enrolled in the 3-year cohort study. MAIN OUTCOME MEASURES: The incidences of MCI among subjects with normal cognition; the annual conversion rates into Alzheimer disease in MCI patients and subjects with normal cognition; the relative risks (RR) and 95% confidence interval (95% CI) of MCI and normal cognition developing into Alzheimer disease. RESULTS: The MCI group and normal cognition group were followed up once every year for 3 years. Of the 216 MCI patients, 7 died, and 209 were followed up actually, and the follow-up rate was 96.8%. Of the 2 302 subjects with normal cognition, 36 died, and 2 266 were followed up actually,and the follow-up rate was 98.4%. ① In the elderly subjects with normal cognition, the annual incidence of MCI was 4.8%, and those of dementia and Alzheimer disease were 1.3% and 0.8 respectively. ② The annual in cidence rates of dementia and Alzheimer disease in MCI patients were 8.1% and 5.6% respectively, which were insignificantly different between males and females (P ＞ 0.05). ③ The incidence rates of dementia and Alzheimer disease showed a descending trend with the elevation of educational level in both the MCI patients (trend x2 =5.57, P=0.02; trend x2 =4.92, P=0.03) and the subjects with normal cognition (trend x2 =23.1, P＜ 0.001; trend x2 =18.0, P ＜ 0.001). ④ The annual incidence rates of dementia and Alzheimer disease showed an ascending trend with aging in both the MCI patients (trend x2 =14.6, P ＜ 0.01; trend x2 =13.9, P ＜ 0.01) and the subjects with normal cognition (trend x2 =32.3, P ＜ 0.01; trend x2=23.8, P ＜ 0.01). ⑤ The relative risks of the conversion into dementia and Alz heimer disease in MCI patients were 6.4 and 7.4 times as many as those in the subjects with normal cognition.CONCLUSION: The risks of conversion into dementia and Alzheimer disease in elderly MCI patients are far higher than those in elderly people with normal cognition. It should be reinforced to monitor elderly MCI patients, who are the of high risk group of dementia.