Outcomes of mild cognitive impairment by definition: A population study

Background: Mild cognitive impairment (MCI) has been defined in several ways. Objective: To determine the 1-year outcomes of MCI by different definitions at the population level. Design: Inception cohort with 1-year follow-up. Participants were classified as having MCI using the following definitions operationalized for this study: amnestic MCI by Mayo criteria, expanded MCI by International Working Group criteria, Clinical Dementia Rating (CDR) =0.5, and a purely cognitive classification into amnestic and nonamnestic MCI. Setting: General community. Participants: Stratified random population-based sample of 1982 individuals 65 years and older. Main Outcome Measures: For each MCI definition, there were 3 possible outcomes: worsening (progression to dementia [CDR≥1] or severe cognitive impairment), improvement (reversion toCDR=0 or normal cognition), and stability (unchangedCDRor cognitive status). Results: Regardless of MCI definition, over 1 year, a small proportion of participants progressed to CDR>1 (range, 0%-3%) or severe cognitive impairment (0%-20%) at rates higher than their cognitively normal peers. Somewhat larger proportions of participants improved or reverted to normal (6%-53%). Most participants remained stable (29%-92%). Where definitions focused on memory impairment and on multiple cognitive domains, higher proportions progressed and lower proportions reverted on the CDR. Conclusions: As ascertained by several operational definitions, MCI is a heterogeneous entity at the population level but progresses to dementia at rates higher than in normal elderly individuals. Proportions of participants progressing to dementia are lower and proportions reverting to normal are higher than in clinical populations. Memory impairments and impairments in multiple domains lead to greater progression and lesser improvement. Research criteria may benefit from validation at the community level before incorporation into clinical practice.