Prevalence of mild cognitive impairment subtypes in patients attending a memory outpatient clinic--comparison of two modes of mild cognitive impairment classification. Results of the Vienna Conversion to Dementia Study.

BACKGROUND

Early detection of dementia is becoming more and more important owing to the advent of pharmacologic treatment.

OBJECTIVE

The goals of this study were to establish prevalence of mild cognitive impairment (MCI) subtypes in an outpatient memory clinic cohort using two different modes of MCI determination.

DESIGN

Consecutive patients complaining of cognitive problems who came to the memory outpatient clinic for assessment of a possible cognitive disorder were included in the study.

SETTING

Academic medical center.

PARTICIPANTS

Six hundred eighty consecutive patients complaining about cognitive problems who came to the memory outpatient clinic for assessment of a possible cognitive disorder and fulfilled the inclusion criteria were included in the study. For 676 patients, sufficient data for MCI classification were available.

RESULTS

Categorizing MCI patients into MCI subtypes according to the minimum mode of MCI classification revealed the following results: 106 patients (15.7%) were categorized as cognitively healthy, whereas 570 patients (84.3%) met the criteria for MCI. MCI patients were subtyped as amnestic mild cognitive impairment (aMCI) single domain (31 patients; 4.6%), aMCI multiple domain (226 patients; 33.4%), non-aMCI single domain (125 patients; 18.5%), and non-aMCI multiple domain (188 patients; 27.8%). Categorizing MCI patients into MCI subtypes according to the mean mode of MCI classification revealed the following results: 409 patients (60.5%) were categorized as cognitively healthy, whereas 267 patients (39.5%) met the criteria for MCI. MCI patients were subtyped as aMCI single domain (47 patients; 6.9%), aMCI multiple domain (57 patients; 8.5%), non-aMCI single domain (97 patients; 14.3%), and non-aMCI multiple domain (66 patients; 9.8%).

CONCLUSION

MCI diagnosis frequencies are substantially affected by the criteria used for estimation of MCI. The effect of modifying the presence of impairment on a single cognitive measure versus the presence of impairment on a mean composite score of a certain domain differed considerably, ranging from 39.5% to 84.3%, indicating the importance of the development of guidelines for operationalizing MCI.