Distinct dynamic profiles of microglial activation are associated with progression of Alzheimer's disease.
Level 3 - non-randomized controlled study
Prospective longitudinal cohort study comparing Alzheimer's disease patients and controls over a 2-year follow-up.
PubMed 29608645 · doi:10.1093/brain/awy079
What was done
Participants with prodromal Alzheimer's disease (n = 33), demented Alzheimer's disease (n = 19), and healthy controls (n = 17) underwent baseline clinical assessment, brain MRI, 11C-PiB PET, TSPO genotyping, and 18F-DPA-714 PET to measure microglial activation. Subjects were followed annually for 2 years to evaluate functional (Clinical Dementia Rating), cognitive (Mini-Mental State Examination), and structural (hippocampal atrophy) outcomes. At study completion, 24 patients with Alzheimer's disease and 15 controls underwent a second 18F-DPA-714 PET scan to evaluate longitudinal microglial dynamics.
What was found
Initial 18F-DPA-714 binding was higher in prodromal and demented Alzheimer's patients than in controls. Baseline binding was higher in slow decliners compared to fast decliners and negatively correlated with CDR Sum of Boxes increase, MMSE score loss, and hippocampal atrophy progression. Over 2 years, 18F-DPA-714 binding increased faster in Alzheimer's patients (mean 13.2% per year; 15.8% prodromal, 8.3% demented) than controls (4.2% per year). Longitudinal increases in binding positively correlated with cognitive decline, CDR worsening, and hippocampal atrophy, independent of baseline PiB-PET amyloid uptake.
Why it matters
This study shows that microglial activation exhibits distinct temporal dynamics in Alzheimer's disease: early microglial activation associates with slower clinical progression, whereas progressive secondary neuroinflammation tracks rapid cognitive and structural deterioration.
Limits
The total sample size was modest (69 participants at baseline), and repeat PET imaging was completed in only 39 subjects (24 Alzheimer's disease, 15 controls). The 2-year follow-up period is short relative to the multi-decade trajectory of Alzheimer's disease. TSPO PET serves as an indirect proxy for neuroinflammation and cannot distinguish specific protective versus detrimental microglial phenotypes.
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