Abstract
Objective: To examine the persistence of concussion-related symptoms following injury as a function of mechanism of injury (high-level blast [HLB] vs impact) and low-level blast (LLB) exposure among Marines.
Setting: Upon return from deployment and approximately 6 months later, respectively, Marines completed the Post-Deployment Health Assessment and Post-Deployment Health Re-Assessment in an operational or clinic setting.
Participants: Data from active duty enlisted Marines who completed both assessments (n = 102 075) and who reported a potentially mild traumatic brain injury (mTBI)-inducing event and completed an mTBI screen (n = 8106) were analyzed.
Design: This was a retrospective cohort study of Marines deployed between 2008 and 2012. Marines were categorized into groups with relatively high versus low risk for occupational risk of LLB exposure. A mixed model analysis of variance was used to examine the number of symptoms Marines reported experiencing during deployment as a function of probable concussion, HLB exposure, occupational risk, type of symptom, and time of measurement.
Main Measures: Self-reported deployment exposures including HLB, probable mTBIs, and occupational risk of LLB exposure were identified. Outcomes included the proportion of neurological, musculoskeletal, and immunological symptoms for which Marines reported seeking care during and following deployment were analyzed.
Results: Probable HLB-induced mTBIs (vs impact-induced) were associated with significantly more neurological symptoms at return from deployment and approximately 6 months later. Although symptom reporting decreased at statistically equivalent rates regardless of mechanism of injury, those with a probable HLB-induced concussion continued to report elevated symptomology post-deployment. Additionally, Marines with probable concussion working in occupations with LLB exposure reported elevated levels of persistent neurological symptoms. Both HLB and LLB exposure were associated with neurological symptoms that persisted following deployment.
Conclusion: These findings suggest that blast-induced brain injuries may be fundamentally different from impact-induced injuries, and that additional screening and symptomatic treatment for blast-exposed patients may be warranted.