Mild cognitive impairment as a clinical entity and treatment target

Mild cognitive impairment is an evolving construct. While appropriate questions have been raised concerning its definition, outcome, and potential treatments, considerable progress has been made. We agree with Gauthier and Touchon⁴ that MCI is heterogeneous. The heterogeneity reflects a refinement of the entity rather than a weakness. Just as the construct of dementia has been refined over the years to reflect increasing sophistication in diagnostic skill, so has the characterization of MCI been refined. If the approach to classifying the syndrome of MCI into multiple subtypes is combined with the presumed etiology, much of the variability in the literature can be resolved. The construct is useful both for clinical as well as research purposes. If used in a systematic fashion, it can help characterize the prodromal states of several types of dementia. If specific criteria are used including etiology, it can predict clinically probable AD with high specificity, and this provides physicians and investigators an opportunity to recognize, counsel, and ultimately treat the condition before it advances to fully expressed dementia. In essence, we have to be able to move the diagnostic threshold for these disorders back to earlier stages of impairment with the anticipation of developing appropriate therapies to intervene at these stages. Ideally, we would like to develop markers that predict the future development of dementia and intervene with safe and effective therapies to truly prevent AD and the other dementing disorders.