[Outcome and cognitive changes of mild cognitive impairment in the elderly: a follow-up study of 47 cases].

OBJECTIVE: To examine the cognitive changes and outcome of mild cognitive impairment (MCI) in the elderly and to explore the predictive factors of development from MCI into dementia.

METHOD: A cross-sectional and longitudinal parallel cohort study design was conducted among 47 patients with MCI (MCI group), aged 72.4 +/- 7.1, and 50 sex, marital status, and professional structure-matched normal controls (NC group), aged 67.9 +/- 5.3, using the Neuropsychological Battery of Cognitive Assessment Instruments developed by World Health Organization (WHO-BCAI) and the Wechsler Memory Scale (WMS) to assess the cognitive function. Follow-up was conducted for 34.0 +/- 1.8 months. The diagnosis of dementia was based on the criteria in the Diagnostic and Statistical Manual-IV.

RESULTS: Dementia was diagnosed in 13 of the 47 MCI patients with a prevalence rate of 27.7%, significantly higher than that in the NC group (2.0%, 1/50, P < 0.01). The mean total score of mini-mental status examination (MMSE) of the MCI group decreased by 2.2 +/- 3.7, significantly more than that of the NC group (1.0 +/- 1.9, P < 0.01). The mean total mental quotient (MQ) of the MCI group decreased by 12.6 +/- 17.3, significantly more than that of the NC group (3.9 +/- 8.4, P < 0.01). The values of MMSE and MQ of the 13 cases in the MCI group who developed into dementia patients decreased by 5.5 +/- 2.8 and 30.0 +/- 18.0 respectively. The WHO-BCAI assessment demonstrated that the scores of performance of verbal learning, verbal fluency, visual reasoning, trail making, sorting and spatial construct tests of the cases in the MCI group who developed into dementia patients were significantly poorer than those of the NC group (P < 0.01). Logistic analysis based on the baseline assessment suggested that the total score of MMSE and its subtest of orientation, score of orientation memory of WMS, and the scores of performance of trail making, attention, and delayed recall tested by WHO-BCAI were all statistically significant predictive factors for MCI converting into dementia (P < 0.01 or 0.05). The predictive accuracy rates of MMSE, WMS, and WHO-BCAI were 70.3%, 78.4% and 90.7% respectively.

CONCLUSION: MCI diagnosed based on the criteria of pure MCI modified by the authors is indeed a transitional state from normal aging to dementia, especially Alzheimer's type of dementia. The cognitive change for MCI converting into dementia is characterized in the areas of orientation, attention, speech and executive function. These predictive factors for MCI to develop dementia are valuable in early detection and prevention of dementia in the elderly.