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From mild cognitive impairment to subjective cognitive decline: conceptual and methodological evolution

Authors Cheng YW, Chen TF, Chiu MJ

Received 28 September 2016

Accepted for publication 9 December 2016

Published 16 February 2017 Volume 2017:13 Pages 491—498

DOI https://doi.org/10.2147/NDT.S123428

Checked for plagiarism Yes

Review by Single-blind

Peer reviewers approved by Dr Colin Mak

Peer reviewer comments 5

Editor who approved publication: Professor Wai Kwong Tang

Yu-Wen Cheng,1 Ta-Fu Chen,2 Ming-Jang Chiu2,3

1Department of Neurology, National Taiwan University Hospital, Hsin-Chu Branch, Hsin-Chu, Taiwan; 2Department of Neurology, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei, Taiwan; 3Department of Psychology, College of Science, National Taiwan University, Taipei, Taiwan

Abstract: Identification of subjects at the early stages of Alzheimer’s disease (AD) is fundamental for drug development and possible intervention or prevention of cognitive decline. The concept of mild cognitive impairment (MCI) evolved during the past two decades to define subjects at the transitional stage between normal aging and dementia. Evidence from cross-sectional and longitudinal studies has shown that MCI is associated with an increased risk of positive AD biomarkers and an increased annual conversion rate of 5%–17% to AD. The presence of AD biomarkers in subjects with MCI was associated with an even higher risk of progression to dementia. However, earlier clinical trials for pharmacotherapy in subjects with MCI were disappointing. To extend the spectrum of AD to an earlier stage before MCI, subjective cognitive decline (SCD) was introduced and was defined as self-reported cognitive decline before the deficits could be detected by cognitive tests. Subjects with SCD have an increased risk of underlying AD pathology. However, SCD can also develop secondary to other heterogeneous etiologies, including other neurodegenerative and psychiatric diseases, personality traits, physical conditions, and medication use. Several clinical and biomarker features were proposed to predict risk of conversion to AD in subjects with SCD. Further longitudinal studies are needed to support the validity of these high-risk features.

Keywords: mild cognitive impairment, subjective cognitive decline, preclinical Alzheimer’s disease, Alzheimer’s disease

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