Mild cognitive impairment: a concept in evolution

Abstract

The construct of mild cognitive impairment (MCI) has evolved over the past 10 years since the publication of the new MCI definition at the Key Symposium in 2003, but the core criteria have remained unchanged. The construct has been extensively used worldwide, both in clinical and in research settings, to define the grey area between intact cognitive functioning and clinical dementia. A rich set of data regarding occurrence, risk factors and progression of MCI has been generated. Discrepancies between studies can be mostly explained by differences in the operationalization of the criteria, differences in the setting where the criteria have been applied, selection of subjects and length of follow-up in longitudinal studies. Major controversial issues that remain to be further explored are algorithmic versus clinical classification, reliability of clinical judgment, temporal changes in cognitive performances and predictivity of putative biomarkers. Some suggestions to further develop the MCI construct include the tailoring of the clinical criteria to specific populations and to specific contexts. The addition of biomarkers to the clinical phenotypes is promising but requires deeper investigation. Translation of findings from the specialty clinic to the population setting, although challenging, will enhance uniformity of outcomes. More longitudinal population-based studies on cognitive ageing and MCI need to be performed to clarify all these issues.

Keywords: Alzheimer's disease; dementia; memory impairment; mild cognitive impairment.

Conflict of interest statement

Conflict of interest statement

Dr Petersen declares the following: Pfizer, Inc: Chair, Data monitoring committee, Janssen Alzheimer Immunotherapy: Chair, Data monitoring committee, GE Heathcare: Consultatnt, Roche Inc: Consultant.

© 2014 The Association for the Publication of the Journal of Internal Medicine.

Figures

Fig. 1

Comparison of current criteria for mild cognitive impairment (MCI). The criteria outlined in blue were proposed at the Key Symposium in 2003 [7, 8]. Other criteria include those of the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) [15] and MCI due to Alzheimer’s disease (AD) [16]. Aβ amyloid-beta; MRI,magnetic resonance imaging; FDG PET, fluorodeoxyglucose positron emission tomography; tau, tau protein.