Global Disability Trajectories Over the First Decade Following Combat Concussion

Association of Clinical TBI Severity and Military Factors With Veteran TBI Service-Connected Disability Ratings and Total Compensation: A Long-Term Impact of Military Brain Injury Consortium (LIMBIC) Study

OBJECTIVE

To understand how traumatic brain injury (TBI) clinical severity and military factors were associated with the likelihood of receiving a TBI service-connected disability (SCD) determination and monthly total SCD compensation among Veterans.

SETTING

Veterans Health Administration (VHA) and Veterans Benefits Administration (VBA).

PARTICIPANTS

1 319 590 veterans with a VBA SCD rating who entered the VHA between October 1, 2000, and September 24, 2019.

DESIGN

This retrospective study analyzed the association of TBI severity and military factors with a TBI SCD determination, TBI SCD rating percentage, and monthly total SCD compensation. Administrative VHA and VBA records were utilized.

MAIN MEASURES

Any TBI SCD determination, TBI SCD rating percentage, and monthly SCD compensation.

RESULTS

93 911 (7.1%) Veterans had an SCD rating for TBI. TBI SCD increased monthly total compensation by $362 (95% CI 353, 370) in bivariate and $45 (95% CI 38, 52) in adjusted models. Females had lower TBI SCD percentage (-3.03; 95% CI -3.92, -2.14) but higher monthly compensation ($37; 95% CI 33, 42). TBI severity was associated with increasing TBI SCD percentage and monthly SCD compensation. In adjusted models, deployment (-2.36; 95% CI -3.02, -1.69) was associated with lower TBI SCD percentage but not monthly compensation, while combat exposure was not associated with TBI SCD percentage but was associated with higher compensation ($46; 95% CI 40, 53).

CONCLUSION

TBI severity was significantly associated with TBI SCD determination and TBI SCD rating percentage, in addition to overall SCD compensation. Although deployment was significantly associated with TBI SCD determination, non-deployment was associated with higher TBI SCD percent ratings. These results may be explained by TBI occurring in non-deployment military settings, such as training. This highlights the need to study risk for TBI in the general military environment to ensure that all military-related TBI exposures are recognized and that any related disability is appropriately compensated.

Gut Microbial Composition Is Associated with Symptom Self-Report in Trauma-Exposed Iraq and Afghanistan Veterans

Iraq and Afghanistan War-era Veterans are at elevated risk for physical injuries and psychiatric illnesses, in particular the polytrauma triad of mild traumatic brain injury (mTBI), post-traumatic stress disorder (PTSD), and chronic pain. The gut microbiome has been implicated in modulation of critical processes beyond digestion, including immune system functioning and stress responsivity, and may be an important factor in understanding physical and mental health outcomes following deployment and trauma exposure. However, minimal research to date has sought to characterize gut microbiome composition in this population. Male Veterans of the conflicts in Iraq and Afghanistan who previously completed a Veterans Affairs' comprehensive TBI evaluation were enrolled in the current study. Participants completed self-report measures of PTSD symptom severity, pain intensity and interference, fatigue, cognitive symptoms, substance use, and sleep quality. They also submitted fecal samples, and metagenomic sequencing was used to calculate alpha and beta diversity and taxonomic microbial composition. Associations between microbiome data and clinical variables were then examined. Alpha and beta diversity measures were not significantly correlated with clinical outcomes. Fatigue, post-concussive symptoms, executive function symptoms, and cannabis use were associated with differences in gut microbial composition, specifically Verrucomicrobiota. Together, results suggest that altered gut microbiome composition is associated with psychiatric and cognitive symptoms in Veterans and highlight a potential new therapeutic target of interest. Future research is needed to examine whether probiotic treatment is effective for reducing symptoms common in this clinical population.

Reduction of epinephrine in the lumbar spinal cord following repetitive blast-induced traumatic brain injury in rats

Traumatic brain injury-induced unfavorable outcomes in human patients have independently been associated with dysregulated levels of monoamines, especially epinephrine, although few preclinical studies have examined the epinephrine level in the central nervous system after traumatic brain injury. Epinephrine has been shown to regulate the activities of spinal motoneurons as well as increase the heart rate, blood pressure, and blood flow to the hindlimb muscles. Therefore, the purpose of the present study was to determine the impact of repeated blast-induced traumatic brain injury on the epinephrine levels in several function-specific central nervous system regions in rats. Following three repeated blast injuries at 3-day intervals, the hippocampus, motor cortex, locus coeruleus, vestibular nuclei, and lumbar spinal cord were harvested at post-injury day eight and processed for epinephrine assays using a high-sensitive electrochemical detector coupled with high-performance liquid chromatography. Our results showed that the epinephrine levels were significantly decreased in the lumbar spinal cord tissues of blast-induced traumatic brain injury animals compared to the levels detected in age- and sex-matched sham controls. In other function-specific central nervous system regions, although the epinephrine levels were slightly altered following blast-induced traumatic brain injury, they were not statistically significant. These results suggest that blast injury-induced significant downregulation of epinephrine in the lumbar spinal cord could negatively impact the motor and cardiovascular function. This is the first report to show altered epinephrine levels in the spinal cord following repetitive mild blast-induced traumatic brain injury.

Prospective memory performance in veterans with and without histories of mild traumatic brain injury: effect of the apolipoprotein E (APOE) ε4 genotype

OBJECTIVE

Identifying factors that moderate cognitive outcomes following mild traumatic brain injury (mTBI) is crucial. Prospective memory (PM) is a cognitive domain of interest in mTBI recovery as it may be especially sensitive to TBI-related changes. Since studies show that genetic status - particularly possession of the apolipoprotein E (APOE) ε4 allele - can modify PM performance, we investigated associations between mTBI status and APOE-ε4 genotype on PM performance in a well-characterized sample of Veterans with neurotrauma histories.

METHODS

59 Veterans (mTBI = 33, Military Controls [MCs] = 26; age range: 24-50; average years post-injury = 10.41) underwent a structured clinical interview, neuropsychological assessment, and genotyping. The Memory for Intentions Test (MIST) measured PM across multiple subscales. ANCOVAs, adjusting for age and posttraumatic stress symptoms, tested the effects of mTBI status (mTBI vs. MC) and ε4 status (ε4+ vs. ε4-) on MIST scores.

RESULTS

Veterans with mTBI history performed more poorly compared to MCs on the MIST 15-min delay (p=.002, ηp2 =.160), Time Cue (p = .003, ηp2 =.157), and PM Total (p = .016, ηp2 =.102). Those with at least one copy of the ε4 allele performed more poorly compared to ε4- Veterans on the MIST 15-min delay (p = .011, ηp2 =.113) and PM Total (p = .048, ηp2 = .071). No significant interactions were observed between mTBI and APOE-ε4 status on MIST outcomes (ps>.25). Within the mTBI group, APOE-ε4+ Veterans performed worse than APOE-ε4- Veterans on the MIST 15-min delay subscale (p = .031, ηp2 = .150).

CONCLUSIONS

mTBI history and APOE-ε4 genotype status were independently associated with worse PM performance compared to those without head injury histories or possession of the APOE-e4 genotype. Performance on the MIST 15-min delay was worse in Veterans with both risk factors (mTBI history and APOE-ε4 positivity). Findings suggest that genetic status may modify outcomes even in relatively young Veterans with mTBI histories. Future research examining longitudinal associations and links to neuroimaging and biomarker data are needed.

Blast-related mild TBI: LIMBIC-CENC focused review with implications commentary

BACKGROUND

A significant factor for the high prevalence of traumatic brain injury (TBI) among U.S. service members is their exposure to explosive munitions leading to blast-related TBI. Our understanding of the specific clinical effects of mild TBI having a component of blast mechanism remains limited compared to pure blunt mechanisms.

OBJECTIVE

The purpose of this review is to provide a synopsis of clinical research findings on the long-term effects of blast-related mild TBI derived to date from the Long-Term Impact of Military-Relevant Brain Injury Consortium - Chronic Effects of Neurotrauma Consortium (LIMBIC-CENC).

METHODS

Publications on blast-related mild TBI from LIMBIC-CENC and the LIMBIC-CENC prospective longitudinal study (PLS) cohort were reviewed and their findings summarized. Findings from the broader literature on blast-related mild TBI that evaluate similar outcomes are additionally reviewed for a perspective on the state of the literature.

RESULTS

The most consistent and compelling evidence for long-term effects of blast-related TBI is for poorer psychological health, greater healthcare utilization and disability levels, neuroimaging impacts on brain structure and function, and greater headache impact on daily life. To date, evidence for chronic cognitive performance deficits from blast-related mild TBI is limited, but futher research including crucial longitudinal data is needed.

CONCLUSION

Commentary is provided on: how LIMBIC-CENC findings assimilate with the broader literature; ongoing research gaps alongside future research needs and priorities; how the scientific community can utilize the LIMBIC-CENC database for independent or collaborative research; and how the evidence from the clinical research should be assimilated into clinical practice.

Blast-Induced Neurotrauma Results in Spatially Distinct Gray Matter Alteration Alongside Hormonal Alteration: A Preliminary Investigation

Blast-induced neurotrauma (BINT) frequently occurs during military training and deployment and has been linked to long-term neuropsychological and neurocognitive changes, and changes in brain structure. As military personnel experience frequent exposures to stress, BINT may negatively influence stress coping abilities. This study aimed to determine the effects of BINT on gray matter volume and hormonal alteration. Participants were Canadian Armed Forces personnel and veterans with a history of BINT (n = 12), and first responder controls (n = 8), recruited due to their characteristic occupational stress professions. Whole saliva was collected via passive drool on the morning of testing and analyzed for testosterone (pg/mL), cortisol (μg/dL), and testosterone/cortisol (T/C) ratio. Voxel-based morphometry was performed to compare gray matter (GM) volume, alongside measurement of cortical thickness and subcortical volumes. Saliva analyses revealed distinct alterations following BINT, with significantly elevated testosterone and T/C ratio. Widespread and largely symmetric loci of reduced GM were found specific to BINT, particularly in the temporal gyrus, precuneus, and thalamus. These findings suggest that BINT affects hypothalamic-pituitary-adrenal and -gonadal axis function, and causes anatomically-specific GM loss, which were not observed in a comparator group with similar occupational stressors. These findings support BINT as a unique injury with distinct structural and endocrine consequences.

Surveying the Landscape: A Review of Longitudinal TBI Studies in Service Member and Veteran Populations

Traumatic brain injury (TBI) is known to be a signature wound of the post-9/11 conflicts. In response, the U.S. Department of Defense (DOD) and other federal organizations have directed significant investments toward TBI research on characterizing injury populations and understanding long-term outcomes. To address legislative requirements and research gaps, several observational, longitudinal TBI studies were initiated as an effective means of investigating TBI clinical management, outcomes, and recovery. This review synthesizes the landscape (i.e., requirements and gaps, infrastructure, geography, timelines, TBI severity definitions, military and injury populations of interest, and measures) of DOD-funded longitudinal TBI studies being conducted in service member and veteran (SMV) populations. Based on the landscape described here, we present recommended actions and solutions that would allow a consolidated and cooperative future state of longitudinal TBI research, optimized continued investments, and advances in the state of the science without redundancy.