Close proximity to blast: No long-term or lasting effect on cognitive performance in service members with and without TBI during blast exposure

A review of long-term outcomes of repetitive concussive and subconcussive blast exposures in the military and limitations of the literature

Objective: The purpose of this review is to summarize the long-term cognitive, psychological, fluid biomarker, and neuroimaging outcomes following repetitive concussive and subconcussive blast exposures sustained through a military career. Method/Results: A review of the literature was conducted, with 450 manuscripts originally identified and 44 manuscripts ultimately included in the review. The most robust studies investigating how repetitive concussive and subconcussive exposures related to cognitive performance suggest there is no meaningful impact. Although there are minimal studies that suggest some small impacts on neuroimaging and fluid biomarkers, most findings have been in very small samples and fail to replicate. Both repetitive blast mTBI and subconcussive blasts appeared to be associated with increased self-reported symptoms. Many of the studies suffered from small sample size, failure to correct for multiple comparisons, and inappropriate control groups. Conclusions: Overall, there is little evidence to support that repetitive blast mTBIs or subconcussive blast exposures have a lasting impact on cognition, neuroimaging, or fluid biomarkers. In contrast, there does appear to be a relationship between these exposures and self-reported psychological functioning, though it is unclear what mechanism drives this relationship. Small sample size, lack of correction for multiple comparisons, limited control groups, lack of consideration of important covariates, limited diversity of samples, and lack of reliable and valid measures for assessment of blast exposure are major limitations restricting this research. Patients should be encouraged that while research is ongoing, there is little to currently suggest long-term cognitive or neurological damage following repetitive blast exposure.

Lifetime blast exposure is not related to cognitive performance or psychiatric symptoms in US military personnel

Objective: The present study aimed to examine the impact of lifetime blast exposure (LBE) on neuropsychological functioning in service members and veterans (SMVs). Method: Participants were 282 SMVs, with and without history of traumatic brain injury (TBI), who were prospectively enrolled in a Defense and Veterans Brain Injury Center (DVBIC)-Traumatic Brain Injury Center of Excellence (TBICoE) Longitudinal TBI Study. A cross-sectional analysis of baseline data was conducted. LBE was based on two factors: Military Occupational Speciality (MOS) and SMV self-report. Participants were divided into three groups based on LBE: Blast Naive (n = 61), Blast + Low Risk MOS (n = 96), Blast + High Risk MOS (n = 125). Multivariate analysis of variance (MANOVA) was used to examine group differences on neurocognitive domains and the Minnesota Multiphasic Personality Inventory-2 Restructured Form. Results: There were no statistically significant differences in attention/working memory, processing speed, executive functioning, and memory (Fs < 1.75, ps > .1, ηp2s < .032) or in General Cognition (Fs < 0.95, ps > .3, ηp2s < .008). Prior to correction for covariates, lifetime blast exposure was related to Restructured Clinical (F(18,542) = 1.77, p = .026, ηp2 = .055), Somatic/Cognitive (F(10,550) = 1.99, p = .033, ηp2 = .035), and Externalizing Scales (F(8,552) = 2.17, p = .028, ηp2 = .030); however, these relationships did not remain significant after correction for covariates (Fs < 1.53, ps > .145, ηp2s < .032). Conclusions: We did not find evidence of a relationship between LBE and neurocognitive performance or psychiatric symptoms. This stands in contrast to prior studies demonstrating an association between lifetime blast exposure and highly sensitive blood biomarkers and/or neuroimaging. Overall, findings suggest the neuropsychological impact of lifetime blast exposure is minimal in individuals remaining in or recently retired from military service.