Objective: Mild cognitive impairment (MCI) is variably defined. We sought to examine the effects of this variability on prevalence estimates and 5-year outcomes of MCI.
Design: 5-year prospective cohort study.
Materials and Methods: We examined 1,790 adults 65 years of age or older who completed neuropsychological and clinical assessments in the Canadian Study of Health and Aging.
Results: The most commonly used case definition of MCI yielded a population prevalence estimate of 1.03% (95% CI 0.66-1.40). Eliminating the requirements for subjective memory complaints and intact instrumental ADL increased the prevalence to 3.02% (CI 2.40-3.64). 5-year outcomes, including the risk of death, institutionalization, and dementia, were not distinctly different for various case definitions of MCI, but all were at increased risk of institutionalization (RR 2.3-5.2) and dementia (RR 9.3-19.7). Regardless of the case definition, most people with MCI developed dementia, chiefly Alzheimer’s disease. Still, for each case definition, almost one-third were considered to have no cognitive impairment after 5 years.
Conclusion: Memory complaints and intact IADL’s may be unnecessary requirements for a case definition of MCI in population-based samples. The MCI criteria identify people at increased risk of Alzheimer’s disease, but the potential for improvement of a substantial proportion of those with MCI needs to be acknowledged.
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