The relationship between hippocampal changes in healthy aging and Alzheimer's disease: a systematic literature review.
Level 3 - non-randomized controlled study
Systematic review of longitudinal observational MRI cohort studies
PubMed 39210976 · doi:10.3389/fnagi.2024.1390574
What was done
A PRISMA-guided systematic literature review was conducted searching PubMed up to September 15, 2022, for longitudinal magnetic resonance imaging (MRI) studies reporting hippocampal volume changes or atrophy rates in cognitively normal aging individuals, individuals with mild cognitive impairment (MCI), and patients with Alzheimer's disease (AD). Two teams of two independent reviewers screened 357 records, assessed 115 full-text articles, and extracted data from 15 eligible studies.
What was found
The abstract provides no specific numerical values, percentages, or pooled statistical effect sizes. Across the 15 included studies, longitudinal reductions in overall hippocampal and subfield volumes and increased rates of atrophy were observed across groups. The magnitude and rate of hippocampal loss were greatest in AD, intermediate in MCI, and lowest in healthy aging, indicating a quantitative continuum rather than distinct qualitative divergence.
Why it matters
This review reinforces neuroimaging evidence that hippocampal degeneration follows a continuous gradient across cognitive aging stages. It supports interpreting structural hippocampal loss in MCI and AD as quantitative accelerations of aging-related atrophy.
Limits
The review searched only a single database (PubMed). The abstract reports no quantitative meta-analysis, pooled effect sizes, or confidence intervals. Study-level sample sizes, follow-up durations, imaging protocols, and potential confounding variables across the 15 included cohorts are not reported in the abstract.