Neurological effects of repeated blast exposure in Special Operations personnel.

Exposure to blast overpressure has been a pervasive feature of combat-related injuries. Studies exploring the neurological correlates of repeated low-level blast exposure in career Breachers demonstrated higher levels of tumor necrosis factor alpha (TNFα) and interleukin 6 (IL-6) and decreases in interleukin-10 (IL-10) within brain-derived extracellular vesicles (BDEVs). The current pilot study was initiated in partnership with US Special Operations Command (USSOCOM) to explore whether neuroinflammation is seen within special operators with prior blast exposure. Data was analyzed from 18 service members, inclusive of 9 blast-exposed special operators with an extensive career history of repeated blast exposures and 9 controls matched by age and duration of service. Neuroinflammation was assessed utilizing PET imaging with [^18F]DPA-714. Serum was acquired to assess inflammatory biomarkers within whole serum and BDEs. The Blast Exposure Threshold Survey (BETS) was acquired to determine blast history. Both self-report and neurocognitive measures were acquired to assess cognition. Similarity-driven Multi-view Linear Reconstruction (SiMLR) was used for joint analysis of acquired data. Analysis of BDEVs indicated significant positive associations with a generalized blast exposure value (GBEV) derived from the BETS. SiMLR-based analyses of neuroimaging demonstrated exposure-related relationships between GBEV, PET-neuroinflammation, cortical thickness and volume loss within special operators. Affected brain networks included regions associated with memory retrieval, executive functioning as well as visual and heteromodal processing. Post-hoc assessments of cognitive measures failed to demonstrate significant associations with GBEV. This emerging evidence suggests neuroinflammation may be a key feature of the brain response to blast exposure over a career in operational personnel. The common thread of neuroinflammation observed in blast-exposed populations requires further study.