Mild cognitive impairment: long-term course of four clinical subtypes.
OBJECTIVE: To empirically validate the expanded concept of mild cognitive impairment (MCI), which differentiates between four clinical subtypes-amnestic MCI-single domain, amnestic MCI-multiple domains, nonamnestic MCI-single domain, and nonamnestic MCI-multiple domains-and to examine the prevalence, course, and outcome of these four clinical MCI subtypes. METHODS: We studied a community sample of 980 dementia-free individuals aged 75 years or older who participated in the Leipzig Longitudinal Study of the Aged (LEILA 75+). All participants were examined by neuropsychological testing based on 6 years of observation. The diagnoses of the four clinical MCI subtypes were made according to the original and to slightly modified criteria by Petersen et al. (2001) (both with a cutoff of 1.0 SD and with a cutoff of 1.5 SD). The complete range of outcome types (dementia, death, improvement, stable diagnosis, unstable diagnosis) was described for all subtypes. The relative predictive power of stable MCI for dementia onset was determined. RESULTS: MCI-single domain is more frequent than MCI-multiple domains, and the nonamnestic MCI type is as frequent as the amnestic MCI type. The "MCI modified, 1.0 SD" criteria have the highest relative predictive power for the development of dementia (sensitivity = 74%, specificity = 73%). Alzheimer disease (AD) was the most common type of dementia at follow-up in all but one MCI subtype. Participants with nonamnestic MCI-multiple domains were more likely to progress to a non-AD dementia. CONCLUSIONS: It has been assumed that each MCI subtype is associated with an increased risk for a particular type of dementia. We can only partially agree with this.