Mild cognitive impairment: epidemiology and dementia risk in an elderly Italian population

OBJECTIVES: To investigate prevalence and incidence of mild cognitive impairment (MCI) and its risk of progression to dementia in an elderly Italian population.
DESIGN: Longitudinal.
SETTING: Population-based cohort aged 65 and older resident in an Italian municipality.
PARTICIPANTS: A total of 1,016 subjects underwent baseline evaluation in 1999/2000. In 2003/04, information about cognitive outcome was collected for 745 participants who were free of dementia at baseline.
MEASUREMENTS: MCI (classified as with or without impairment of the memory domain), dementia, Alzheimer's dementia (AD), and vascular dementia (VaD) diagnosed according to current international criteria.
RESULTS: Overall prevalence of MCI was 7.7% (95% confidence interval (CI)=6.1–9.7 %) and was greater with older age and poor education. During 4 years of follow-up, 155 incident MCI cases were diagnosed, with an incidence rate of 76.8 (95% CI=66.8–88.4) per 1,000 person-years. Approximately half of prevalent and incident MCI cases had memory impairment. Compared with normal cognition, multivariable-adjusted risk for progression from MCI with memory impairment to dementia was 4.78 (95% CI=2.78–8.07) for any dementia, 5.92 (95% CI=3.20–10.91) for AD, and 1.61 (95% CI=0.37–7.00) for VaD. No association with dementia risk was found for MCI without memory impairment. Approximately one-third of MCI cases with memory impairment did not progress to dementia.
CONCLUSION: MCI occurs often in this elderly Italian cohort and is associated with greater risk of AD, but only when the impairment involves the memory domain. However, a substantial proportion of MCI cases with memory impairment do not progress to dementia.