Epidemiology, patterns of care and outcomes of traumatic brain injury in deployed military settings: implications for future military operations

Traumatic brain injury: Symptoms to systems in the 21st century

Severe traumatic brain injury (TBI) is a devastating injury with a mortality of ∼ 25-30 %. Despite decades of high-quality research, no drug therapy has reduced mortality. Why is this so? We argue two contributing factors for the lack of effective drug therapies include the use of specific-pathogen free (SPF) animals for translational research and the flawed practice of single-nodal targeting for drug design. A revolution is required to better understand how the whole body responds to TBI, identify new markers of its progression, and discover new system-acting drugs to treat it. In this review, we present a brief history of TBI, discuss its system's pathophysiology and propose a new research strategy for the 21st century. TBI progression develops from injury signals radiating from the primary impact, which can cause local ischemia, hemorrhage, excitotoxicity, cellular depolarization, immune dysfunction, sympathetic hyperactivity, blood-brain barrier breach, coagulopathy and whole-body dysfunction. Metabolic reprograming of immune cells drives neuroinflammation and secondary injury processes. We propose if sympathetic hyperactivity and immune cell activation can be corrected early, cardiovascular function and endothelial-glycocalyx-mitochondrial coupling can be restored, and secondary injury minimized with improved patient outcomes. The therapeutic goal is to switch the injury phenotype to a healing phenotype by restoring homeostasis and maintaining sufficient tissue O2 delivery. We have been developing a small-volume fluid therapy comprising adenosine, lidocaine and magnesium (ALM) to treat TBI and have shown that it blunts the CNS-stress response, supports cardiovascular function and reduces secondary injury. Future research will investigate its suitability for human translation.

Disease and Non-Battle Injury in Deployed Military: A Systematic Review and Meta-analysis

INTRODUCTION

Disease and non-battle injury (DNBI) has historically been the leading casualty type among service members in warfare and a leading health problem confronting military personnel, resulting in significant loss of manpower. Studies show a significant increase in disease burden for DNBI when compared to combat-related injuries. Understanding the causes of and trends in DNBI may help guide efforts to develop preventive measures and help increase medical readiness and resiliency. However, despite its significant disease burden within the military population, DNBI remains less studied than battle injury. In this review, we aimed to evaluate the recently published literature on DNBI and to describe the characteristics of these recently published studies.

MATERIALS AND METHODS

This systematic review is reported in the Prospective Register of Systematic Reviews database. The systematic search for published articles was conducted through July 21, 2022, in Cumulative Index of Nursing and Allied Health, Cochrane Library, Defense Technical Information Center, Embase, and PubMed. Guided by the Preferred Reporting Items for Systematic Reviews and Meta-analyses, the investigators independently screened the reference lists on the Covidence website (covidence.org). An article was excluded if it met any of the following criteria: (1) Published not in English; (2) published before 2010; (3) data used before 2001; (4) case reports, commentaries, and editorial letters; (5) systematic reviews or narrative reviews; (6) used animal models; (7) mechanical or biomechanical studies; (8) outcome was combat injury or non-specified; (9) sample was veterans, DoD civilians, contractors, local nationals, foreign military, and others; (10) sample was U.S. Military academy; (11) sample was non-deployed; (12) bioterrorism study; (13) qualitative study. The full-text review of 2 independent investigators reached 96% overall agreement (166 of 173 articles; κ = 0.89). Disagreements were resolved by a third reviewer. Study characteristics and outcomes were extracted from each article. Risk of bias was assessed using the Newcastle-Ottawa Scale. Meta-analysis of pooled estimates of incidence rates for disease (D), non-battle injury (NBI), and combined DNBI was created using random-effects models.

RESULTS

Of the 3,401 articles, 173 were included for the full review and 29 (16.8%) met all inclusion criteria. Of the 29 studies included, 21 (72.4%) were retrospective designs, 5 (17.2%) were prospective designs, and 3 (10.3%) were surveys. Across all studies, the median number of total cases reported was 1,626 (interquartile range: 619.5-10,203). The results of meta-analyses for 8 studies with reported incidence rates (per 1,000 person-years) for D (n = 3), NBI (n = 7), and DNBI (n = 5) showed pooled incidence rates of 22.18 per 1,000 person-years for D, 19.86 per 1,000 person-years for NBI, and 50.97 per 1,000 person-years for combined DNBI. Among 3 studies with incidence rates for D, NBI, and battle injury, the incidence rates were 20.32 per 1,000 person-years for D, 6.88 per 1,000 person-years for NBI, and 6.83 per 1,000 person-years for battle injury.

CONCLUSIONS

DNBI remains the leading cause of morbidity in conflicts involving the U.S. Military over the last 20 years. More research with stronger designs and consistent measurement is needed to improve medical readiness and maintain force lethality.

LEVEL OF EVIDENCE

Systematic Review and Meta-Analysis, Level III.

Military Traumatic Brain Injury

Traumatic brain injury (TBI) in the military can involve distinct injury mechanisms, diagnostic challenges, treatments, and course of recovery. TBI has played a prominent role in recent conflicts, causing significant morbidity and mortality. Blast-related TBI in combat settings is often accompanied by other physical injuries. Military TBIs of all severities can lead to prolonged recoveries and persistent sequelae. The complex interplay between TBI, pain, and mental health conditions can significantly complicate diagnosis and recovery. Military and veteran health settings and programs provide comprehensive care along the continuum of TBI recovery rehabilitation with the goal of optimizing recovery and function.

Quantitative Pupillometry Predicts Return to Play and Tracks the Clinical Evolution of Mild Traumatic Brain Injury in US Military Academy Cadets: A Military Traumatic Brain Injury Initiative Study

BACKGROUND AND OBJECTIVES

The objective of this study was to determine the utility of the pupillary light reflex use as a biomarker of mild traumatic brain injury (mTBI).

METHODS

This prospective cohort study was conducted at The US Military Academy at West Point. Cadets underwent a standard battery of tests including Balance Error Scoring System, Sports Concussion Assessment Tool Fifth Edition Symptom Survey, Standard Assessment of Concussion, and measure of pupillary responses. Cadets who sustained an mTBI during training events or sports were evaluated with the same battery of tests and pupillometry within 48 hours of the injury (T1), at the initiation of a graded return to activity protocol (T2), and at unrestricted return to activity (T3).

RESULTS

Pupillary light reflex metrics were obtained in 1300 cadets at baseline. During the study period, 68 cadets sustained mTBIs. At T1 (<48 hours), cadets manifested significant postconcussion symptoms (Sports Concussion Assessment Tool Fifth Edition P < .001), and they had decreased cognitive performance (Standardized Assessment of Concussion P < .001) and higher balance error scores (Balance Error Scoring System P < .001) in comparison with their baseline assessment (T0). The clinical parameters showed normalization at time points T2 and T3. The pupillary responses demonstrated a pattern of significant change that returned to normal for several measures, including the difference between the constricted and initial pupillary diameter (T1 P < .001, T2 P < .05), dilation velocity (T1 P < .01, T2 P < .001), and percent of pupillary constriction (T1 P < .05). In addition, a combination of dilation velocity and maximum constriction velocity demonstrates moderate prediction ability regarding who can return to duty before or after 21 days (area under the curve = 0.71, 95% CI [0.56-0.86]).

CONCLUSION

This study's findings indicate that quantitative pupillometry has the potential to assist with injury identification and prediction of symptom severity and duration.

A Narrative Review of Existing and Developing Biomarkers in Acute Traumatic Brain Injury for Potential Military Deployed Use

INTRODUCTION

Traumatic brain injury (TBI) is a leading cause of morbidity and mortality in both adult civilian and military populations. Currently, diagnostic and prognostic methods are limited to imaging and clinical findings. Biomarker measurements offer a potential method to assess head injuries and help predict outcomes, which has a potential benefit to the military, particularly in the deployed setting where imaging modalities are limited. We determine how biomarkers such as ubiquitin C-terminal hydrolase-L1 (UCH-L1), glial fibrillary acidic protein (GFAP), S100B, neurofilament light chain (NFL), and tau proteins can offer important information to guide the diagnosis, acute management, and prognosis of TBI, specifically in military personnel.

MATERIALS AND METHODS

We performed a narrative review of peer-reviewed literature using online databases of Google Scholar and PubMed. We included articles published between 1988 and 2022.

RESULTS

We screened a total of 73 sources finding a total of 39 original research studies that met inclusion for this review. We found five studies that focused on GFAP, four studies that focused on UCH-L1, eight studies that focused on tau proteins, six studies that focused on NFL, and eight studies that focused on S100B. The remainder of the studies included more than one of the biomarkers of interest.

CONCLUSIONS

TBI occurs frequently in the military and civilian settings with limited methods to diagnose and prognosticate outcomes. We highlighted several promising biomarkers for these purposes including S100B, UCH-L1, NFL, GFAP, and tau proteins. S100B and UCH-L1 appear to have the strongest data to date, but further research is necessary. The robust data that explain the optimal timing and, more importantly, trending of these biomarker measurements are necessary before widespread application.

Traumatic brain injury and occupational risk of low-level blast exposure on adverse career outcomes: an examination of administrative and medical separations from Service (2005-2015)

Introduction

Although traumatic brain injury (TBI) has been linked with adverse long-term health, less research has examined whether TBI is linked with non-clinical outcomes including involuntary job loss. Symptoms associated with TBI may influence one's ability to maintain gainful employment including employment in the U.S. military. That influence may impact military service members with exposure to repetitive low-level blast (LLB). Understanding the association between TBI and involuntary job loss outcomes among military populations is particularly important as it may be associated with differences in eligibility for post-service benefits. The purpose of the present research was to determine whether (1) TBI and related conditions are associated with involuntary job loss (i.e., medical and administrative separations from service) among military personnel, and (2) occupational risk of LLB is associated with involuntary job loss in both the presence and absence of clinical diagnoses of TBI and related conditions.

Method

This research leveraged population-level data from the Career History Archival Medical and Personnel System for enlisted personnel who served on active duty between 2005-2015. Risk of LLB exposure was categorized using military occupational specialty as a proxy. Medical diagnoses were identified using ICD-9 codes. Separations for medical and administrative reasons were identified.

Results

Risk for administrative separation differed across medical diagnoses of interest, but those who worked in high-risk occupations were more likely to be administratively separated than those working in low-risk occupations. Risk for medical separation was associated with occupational risk of LLB and each of the diagnoses of interest, though significant interactions suggested that the effects of certain diagnoses of interest (e.g., concussion, cognitive problems, postconcussive syndrome, migraines) on medical separations was greater among those working in high-risk occupations.

Discussion

Taken together, the present research suggests that TBI and associated medical conditions, as well as occupational risk of LLB, are associated with long-term involuntary job loss for medical reasons. This study is the first to demonstrate involuntary military job loss outcomes associated with TBI, mental health conditions, and conditions associated with blast exposure using both inpatient and outpatient population-level data and may have important implications for civilian employment and post-service benefits.

A Review of Electrolyte, Mineral, and Vitamin Changes After Traumatic Brain Injury

INTRODUCTION

Despite the prevalence of traumatic brain injury (TBI) in both civilian and military populations, the management guidelines developed by the Joint Trauma System involve minimal recommendations for electrolyte physiology optimization during the acute phase of TBI recovery. This narrative review aims to assess the current state of the science for electrolyte and mineral derangements found after TBI.

MATERIALS AND METHODS

We used Google Scholar and PubMed to identify literature on electrolyte derangements caused by TBI and supplements that may mitigate secondary injuries after TBI between 1991 and 2022.

RESULTS

We screened 94 sources, of which 26 met all inclusion criteria. Most were retrospective studies (n = 9), followed by clinical trials (n = 7), observational studies (n = 7), and case reports (n = 2). Of those, 29% covered the use of some type of supplement to support recovery after TBI, 28% covered electrolyte or mineral derangements after TBI, 16% covered the mechanisms of secondary injury after TBI and how they are related to mineral and electrolyte derangements, 14% covered current management of TBI, and 13% covered the potential toxic effects of the supplements during TBI recovery.

CONCLUSIONS

Knowledge of mechanisms and subsequent derangements of electrolyte, mineral, and vitamin physiology after TBI remains incomplete. Sodium and potassium tended to be the most well-studied derangements after TBI. Overall, data involving human subjects were limited and mostly involved observational studies. The data on vitamin and mineral effects were limited, and targeted research is needed before further recommendations can be made. Data on electrolyte derangements were stronger, but interventional studies are needed to assess causation.

Application of a Near-infrared Spectroscope by an Extreme Forward Medical Team for the Triage of Casualties With Traumatic Brain Injury

BACKGROUND

During deployment of military medical teams similarly to prehospital practice, without immediate computed tomography scan access, identifying patients requiring neuro-specific care to manage pragmatic triage proves crucial. We assessed the contribution of this portable near-infrared spectroscope (NIRS) handheld device, Infrascanner Model 2000 (InfraScan Inc.; Philadelphia, PA), to screen patients suspected to require specific neurosurgical care.

MATERIALS AND METHODS

This single-center retrospective analysis was based on the data from the medical records of the traumatic brain injured patients. We analyzed all the patients strictly over 18 years old presenting a clinical history of traumatic brain injury (TBI) with a Glasgow Coma Scale (GCS) < 15.

RESULTS

Thirty-seven medical records of patients admitted for TBI met the inclusion criteria for our analysis. The median GCS was 9 [3-14]. Eight patients (21.6%) underwent neurosurgery and 25 (67.6%) required intensive care unit (ICU) admission, after initial assessment and resuscitation. The NIRS was the most sensible to detect intracranial hematoma (n = 21), intracranial hematoma leading to surgery (n = 8), and intracranial hematoma leading to admission in ICU (n = 25). Its negative predictive value was 100% regarding hematomas leading to surgery. False-positive results were encountered in 10 cases (27.0%). Excluding cases harboring confounding extracranial hematomas, parietal area was still the most represented (n = 3).

CONCLUSION

The NIRS was relevant to detect hematoma leading to prompt surgery in our study. The lack of specificity in a nonselected cohort of patients underlines the need to associate simple clinical feature such as neurological deficit and NIRS results to perform rational triage.

Association of Traumatic Brain Injury Severity and Self-Reported Neuropsychiatric Symptoms in Wounded Military Service Members

The impact of traumatic brain injury (TBI) severity and loss of consciousness (LOC) on the development of neuropsychiatric symptoms was studied in injured service members (SMs; n = 1278) evacuated from combat settings between 2003 and 2012. TBI diagnoses of mild TBI (mTBI) or moderate-to-severe TBI (MS-TBI) along with LOC status were identified using International Classification of Diseases, Ninth Revision (ICD-9) codes and the Defense and Veterans Brain Injury Center Standard Surveillance Case Definition for TBI. Self-reported psychiatric symptoms were evaluated for post-traumatic stress disorder (PTSD) with the PTSD Checklist, Civilian Version for PTSD, the Patient Health Questionnaire-9 for major depressive disorder (MDD), and the Patient Health Questionnaire-15 for somatic symptom disorder (SSD) in two time periods post-injury: Assessment Period 1 (AP1, 0.0-2.5 months) and Assessment Period 2 (AP2, 3-12 months). mTBI, but not MS-TBI, was associated with increased neuropsychiatric symptoms: PTSD in AP1 and AP2; MDD in AP1; and SSD in AP2. A subgroup analysis of mTBI with and without LOC revealed that mTBI with LOC, but not mTBI without LOC, was associated with increased symptoms as compared to non-TBI: PTSD in AP1 and AP2; MDD in AP1; and SSD in AP1 and AP2. Moreover, mTBI with LOC was associated with increased MDD symptoms in AP2, and SSD symptoms in AP1 and AP2, compared to mTBI without LOC. These findings reinforce the need for the accurate characterization of TBI severity and a multi-disciplinary approach to address the devastating impacts of TBI in injured SMs.