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.