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

Area of Science:

• Neurology
• Neuroscience
• Gerontology

Background:

• Early identification of Alzheimer's disease (AD) is vital for therapeutic interventions and preventing cognitive decline.
• Mild cognitive impairment (MCI) signifies a transitional stage with increased risk for AD biomarkers and conversion to dementia.
• Subjective cognitive decline (SCD) represents an even earlier stage, characterized by self-reported cognitive changes preceding objective test deficits.

Purpose of the Study:

• To explore the significance of subjective cognitive decline (SCD) and mild cognitive impairment (MCI) in the early detection of Alzheimer's disease (AD).
• To review the association between MCI, AD biomarkers, and conversion rates to dementia.
• To discuss the potential of SCD as a preclinical marker for AD, acknowledging its heterogeneous causes.

Main Methods:

• Review of cross-sectional and longitudinal studies on MCI and AD.
• Analysis of clinical trials involving pharmacotherapy for MCI.
• Examination of proposed clinical and biomarker features for predicting AD conversion in SCD subjects.

Main Results:

• MCI is linked to higher AD biomarker prevalence and an annual conversion rate of 5%-17% to AD.
• AD biomarkers in MCI subjects correlate with an elevated risk of dementia progression.
• SCD subjects show an increased risk of underlying AD pathology, though other etiologies exist.

Conclusions:

• MCI and SCD are critical stages for early AD detection, though earlier trials in MCI were disappointing.
• While SCD indicates elevated AD risk, its diverse origins necessitate careful evaluation.
• Further longitudinal research is required to validate predictive features for AD conversion in SCD individuals.