Neuropsychological outcome from blast versus non-blast: mild traumatic brain injury in U.S. military service members

Effects of mTBI with loss of consciousness on neurobehavioral symptoms, depression, and insomnia in former collegiate and NFL football athletes

OBJECTIVE

Considering that diagnostic decisions about mTBI are often predicated on clinical symptom criteria, it is imperative to determine which initial presentation features of mTBI have prognostic significance for identifying those at high risk for long-term functional impairment.

SETTING

Zoom interview Participants: Male, former NCAA Division I, and professional-level National Football League (NFL) athletes (n = 177) between the ages of 27 and 85 (M = 54.1, SD = 14.7).

DESIGN

Cross-sectional case-control. Main Measures: History of mild TBI, history of loss of consciousness (LOC), depression symptoms, insomnia, neurobehavioral symptoms.

RESULTS

Number of mTBI exposures did not predict neurobehavioral symptoms (B = 0.21, SE = 0.18, p = 0.23), but number of mTBI + LOC events did (B = 2.27, SE = 0.64, p = <.001). Further analysis revealed that the number of mTBI + LOC events predicted neurobehavioral symptoms indirectly through both depression (B = 0.85, 95% CI = [0.27, 1.52) and insomnia (B = 0.81, 95% CI = [0.3, 1.4]). Further, the direct effect of mTBI + LOC events on neurobehavioral symptoms became non-significant when depression and insomnia were added to the model (B = 0.78, SE = 0.45, p = 0.08).

CONCLUSIONS

Findings support LOC at time of injury as an important predictor of long-term outcomes. Additionally, results suggest depression and insomnia as potential mediators in the association between mTBI + LOC and neurobehavioral symptoms. These findings provide justification for early depression and insomnia symptom monitoring following mTBI + LOC.

Head Injury Due to Intimate Partner Violence: Injury Characteristics, Subacute Symptoms, and Receipt of Care

Women survivors of intimate partner violence (IPV) have increased risk of repetitive neurotrauma in their lifetime but have received less research focus compared with populations of athletes, veterans, and emergency department patients. The current study examined the importance of IPV as a contextual mechanism of injury, by comparing women survivors of IPV based on whether they experienced a head injury due to IPV or a head injury not due to IPV. The analyses involved archival data from in-person interviews conducted with women who received a protective order against an intimate partner in Kentucky from 2001 to 2004 (n = 641). Women were excluded if they reported no head injury history (n = 268), resulting in two groups compared based on a retrospective cohort design: 255 women with at least one self-reported IPV-related head injury (M = 33.8 ± 9.0 years old, range: 19-65; 87.5% White) and 118 women with self-reported head injuries due to reasons other than IPV (M = 32.2 ± 9.1 years old, range: 18-62; 89.0% White). Participants were compared on injury characteristics, lifetime physical and sexual IPV severity, subacute symptoms of head injury, and receipt of care for head injury. Compared with women with head injuries unrelated to IPV, women with IPV-related head injuries reported a higher number of lifetime head injuries (Mdn[range]: IPV-related = 3[1-515] vs. non-IPV-related = 1[1-13], p < 0.001, r = 0.51) and a higher number of head injuries involving loss of consciousness (Mdn[range]: IPV-related = 1[1-35] vs. non-IPV-related = 1[1-4], p < 0.001, r = 0.27), but lower rates of hospitalization (IPV-related = 56.1% vs. non-IPV-related = 73.7%, p = 0.001, odds ratio [OR] = 2.20 [95% confidence interval (CI): 1.36, 3.55]) and formal rehabilitation (IPV-related = 3.2% vs. non-IPV-related = 9.4%, p = 0.011, OR = 3.18 [1.24, 8.13]) following head injury. Women with IPV-related head injuries had greater lifetime severity of physical IPV (p < 0.001, d = 0.64 [0.41, 0.86]) and sexual IPV (p < 0.001, d = 0.38 [0.16, 0.60]). Women with IPV-related head injuries endorsed all symptoms at greater rates than women with non-IPV-related head injuries (ps < 0.001), including physical (e.g., headaches: OR = 3.15 [1.81, 5.47]; dizziness: OR = 2.65 [1.68, 4.16]), cognitive (e.g., trouble problem solving: OR = 2.66 [1.53, 4.64]; inattention: OR = 2.39 [1.52, 3.78]), and emotional symptoms (e.g., depression: OR = 7.39 [4.48, 12.20]; anxiety: OR = 4.60 [2.82, 7.51]). The total count of symptoms endorsed was higher for women with IPV-related head injury than women with head injuries unrelated to IPV (p < 0.001, d = 0.71 [0.49, 0.94]). When controlling for lifetime physical and sexual IPV, IPV-related head injury was independently associated with symptom count (β = 0.261, p < 0.001) and accounted for additional variance in symptom count (ΔR2 = 0.06, p < 0.001). Among women survivors of IPV, those reporting IPV-related head injuries reported greater subacute symptoms, but a lower likelihood of being hospitalized or receiving rehabilitative care. Women with self-reported IPV-related head injuries represent an underserved population that is often unevaluated following injury and may have many unmet care needs. Future studies should examine persistent symptoms following IPV-related head injuries and interventions that would be most beneficial for this population.

Field assessment of acute auditory responses to environmental exposures in close quarters tactics training

OBJECTIVE

The purpose of this study was to evaluate auditory performance of military instructors as part of a training course involving noise and blast exposure. Boothless audiometry was used to estimate the test-retest reliability of the auditory measures under realistic field conditions and to determine risk of acute auditory injury during standard training practices.

DESIGN AND STUDY SAMPLE

Thirteen U.S. Marine instructors participated in study activities. An audiologic testing suite embedded in a noise-attenuating headset was used to test various tone detection tasks on subjects after exposure. Acoustic exposures were captured with sound level meters.

RESULTS

Boothless audiometry provide highly repeatable results for various tests of auditory performance in the field environment. In this test population, changes in auditory performance pre- and post-noise exposure were minimal for most measures. The notable exception was binaural (NoSπ) tone detection, which showed significant degradations both as a function of pre- and post-noise exposure on the same day and as a result of cumulative noise exposure over the period of the study.

CONCLUSIONS

Study outcomes are consistent with prior laboratory and epidemiological work and suggest a link between the binaural processes required for NoSπ detection and the hearing-related issues reported by blast-exposed service members.

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

OBJECTIVE

Blast related characteristics may contribute to the diversity of findings on whether mild traumatic brain injury sustained during war zone deployment has lasting cognitive effects. This study aims to evaluate whether a history of blast exposure at close proximity, defined as exposure within 30 feet, has long-term or lasting influences on cognitive outcomes among current and former military personnel.

METHOD

One hundred participants were assigned to one of three groups based on a self-report history of blast exposure during combat deployments: 47 close blast, 14 non-close blast, and 39 comparison participants without blast exposure. Working memory, processing speed, verbal learning/memory, and cognitive flexibility were evaluated using standard neuropsychological tests. In addition, assessment of combat exposure and current post-concussive, posttraumatic stress, and depressive symptoms, and headache was performed via self-report measures. Variables that differed between groups were controlled as covariates.

RESULTS

No group differences survived Bonferroni correction for family-wise error rate; the close blast group did not differ from non-close blast and comparison groups on measures of working memory, processing speed, verbal learning/memory, or cognitive flexibility. Controlling for covariates did not alter these results.

CONCLUSION

No evidence emerged to suggest that a history of close blast exposure was associated with decreased cognitive performance when comparisons were made with the other groups. Limited characterization of blast contexts experienced, self-report of blast distance, and heterogeneity of injury severity within the groups are the main limitations of this study.

Independent and Synergistic Associations Between TBI Characteristics and PTSD Symptom Clusters on Cognitive Performance and Postconcussive Symptoms in Iraq and Afghanistan Veterans

OBJECTIVE

The investigators sought to evaluate the independent and interactive associations between mild traumatic brain injury (mTBI) characteristics and posttraumatic stress disorder (PTSD) symptoms with regard to postconcussive symptoms and cognition among treatment-seeking veterans of the U.S. conflicts in Iraq and Afghanistan.

METHODS

Sixty-seven Iraq and Afghanistan veterans who had a history of mTBI and comorbid PTSD were grouped based on injury mechanism (blast versus nonblast) and number of lifetime mTBIs (one to two versus three or more). Independent associations between mTBI characteristics and PTSD symptom clusters were evaluated with regard to cognition and postconcussive symptoms. Follow-up analyses were conducted to determine any interactive associations between TBI characteristics and PTSD symptom clusters.

RESULTS

Higher PTSD symptoms, particularly hyperarousal, were associated with poorer executive functioning and higher postconcussive symptoms. No direct relationships were observed between PTSD symptom clusters and memory or processing speed. The relationship between hyperarousal and processing speed was moderated by lifetime mTBIs, such that those with a history of at least three mTBIs demonstrated a negative association between hyperarousal and processing speed. Blast-related mTBI history was associated with reduced processing speed, compared with non-blast-related mTBI. However, an interaction was observed such that among those with blast-related mTBI history, higher re-experiencing symptoms were associated with poorer processing speed, whereas veterans without history of blast-related mTBI did not demonstrate an association between processing speed and re-experiencing symptoms.

CONCLUSIONS

Higher hyperarousal and re-experiencing symptoms were associated with reduced processing speed among veterans with repetitive and blast-related mTBI history, respectively. PTSD symptoms, specifically hyperarousal, were associated with poorer executive functioning and higher postconcussive symptoms. Limited associations were found between injury characteristics and cognition chronically following mTBI. However, these results support synergistic effects of specific PTSD symptom clusters and TBI characteristics.

Chronic Effects of Breaching Blast Exposure on Sensory Organization and Postural Limits of Stability

OBJECTIVE

The goal of this effort to investigate if experienced breachers, professionals with a career history of exposure to repeated low-level blasts, exhibited postural instability.

METHODS

Postural data were examined using traditional tests of means and compared to normative data.

RESULTS

Breachers had significantly lower NeuroCom Sensory Organization Test (SOT) visual scores (within normative limits), prolonged Limits of Stability (LOS) test reaction time (30% of breachers and 7% of controls testing abnormal), and slower LOS movement velocity (21% of breachers and 0% of controls testing abnormal) compared to controls.

CONCLUSION

Our LOS test findings are like those previously reported for students in the military breacher training course and seem to indicate that while acute effects of blasts on sensory control of balance fade away, effects on postural LOS persist over time.

Investigation of the Relationship Between Frequency of Blast Exposure, mTBI History, and Post-traumatic Stress Symptoms

INTRODUCTION

Post-traumatic stress disorder (PTSD) and mild traumatic brain injury (mTBI) are common conditions among military personnel that frequently co-occur. This study investigated relationships between self-reported blast exposure, mTBI history, and current post-traumatic stress (PTS) symptoms in a population of active duty service members (n = 202) from the Intensive Outpatient Program at the National Intrepid Center of Excellence.

MATERIALS AND METHODS

Participants were divided into four mTBI groups (0, 1, 2, and 3+) and four blast exposure groups (0-10, 11-100, 101-1,000, and 1,000+). Self-reported lifetime mTBI and blast history were obtained via the Ohio State University TBI Identification Method. PTSS severity was obtained via the PTSD Checklist-Civilian version (PCL-C). Several secondary measures of depression, anxiety, chronic mTBI symptoms, and sleep were also assessed.

RESULTS

The total PCL-C scores differed significantly between mTBI groups, with significant differences detected between the 0/1 mTBI groups and the 3+ mTBI groups. Similar group differences were noted across the three PCL-C subgroup scores (avoidance, re-experiencing, and hyperarousal); however, when comparing the proportion of group participants meeting DSM-IV criteria for each symptom cluster, significant differences between mTBI groups were only noted for avoidance (P = .002). No group differences were noted in PTS symptom severity or distribution between blast groups.

CONCLUSIONS

This study demonstrates an association between lifetime mTBI history and PTS symptom severity and distribution but failed to identify the significant group in self-reported symptoms between the blast exposure groups. Results suggest that additional research is needed to understand the neurobiological mechanism behind these associations and the need for the development of precise assessment tools that are able to more accurately quantify significant lifetime sub-concussive and blast exposures experienced by service members in training and combat operations.

Neuropsychological, Neurocognitive, Vestibular, and Neuroimaging Correlates of Exposure to Repetitive Low-Level Blast Waves: Evidence From Four Nonoverlapping Samples of Canadian Breachers

INTRODUCTION

We assessed the utility of a battery of neuropsychological, neurocognitive, physiological (balance, ataxia, postural tremor), and neuroimaging measures for studying the effects of blast waves in breachers-a population repeatedly exposed to low-level blast during military training and operations.

MATERIALS AND METHODS

Data were collected from four nonoverlapping samples, in the course of similarly structured 4-day breacher training exercises in successive years involving a combination of indoor and outdoor blast events. In all cases, self-report and neuropsychological measures were administered once at baseline (i.e., 1 day before the start of training). In years 1-2, neurocognitive and physiological measures were administered daily before and after training. In years 3-4, neurocognitive data were collected once at baseline. In Year 4, we introduced 3 modifications to our design. First, in addition to breachers, we also collected data from sex-and age-matched military controls at the same time points. Second, we assessed balance, ataxia, and postural tremor immediately following blast exposure "in the field," enabling us to quantify its acute effects. Third, structural magnetic resonance imaging (MRI) scans were acquired before and after the 4-day training exercise to explore differences between breachers and controls at baseline, as well as possible training-related changes using voxel-based morphometry. These design modifications were made to enable us to test additional hypotheses in the context of the same training exercise.

RESULTS

At baseline, scores on the "Rivermead Post Concussion Symptoms Questionnaire," "RAND SF-36" (physical functioning, role limitation due to physical health, social functioning, energy/fatigue, general health), and "Short Musculoskeletal Function Questionnaire" distinguished breachers from controls. Also at baseline, the MRI data revealed that there was greater regional gray matter volume in controls compared to breachers in the right superior frontal gyrus. Balance, ataxia, and postural tremor did not exhibit sensitivity to the acute effects of blast in the field, nor did neurocognitive measures to its cumulative or daily effects.

CONCLUSION

Our exploratory results suggest that self-report neuropsychological measures and structural MRI hold promise as sensitive measures for quantifying the long-term, cumulative effects of blast exposure in breachers. We discuss the limitations of our study and the need for prospective longitudinal data for drawing causal inferences regarding the impact of blast exposure on breachers' health and performance.

Post-traumatic Headache and Mild Traumatic Brain Injury: Brain Networks and Connectivity

PURPOSE OF REVIEW

Post-traumatic headache (PTH) consequent to mild traumatic brain injury (mTBI) is a complex, multidimensional, chronic neurological disorder. The purpose of this review is to evaluate the current neuroimaging studies on mTBI and PTH with a specific focus on brain networks and connectivity patterns.

RECENT FINDINGS

We present findings on PTH incidence and prevalence, as well as the latest neuroimaging research findings on mTBI and PTH. Additionally, we propose a new strategy in studying PTH following mTBI. The diversity and heterogeneity of pathophysiological mechanisms underlying mild traumatic brain injury pose unique challenges on how we interpret neuroimaging findings in PTH. Evaluating alterations in the intrinsic brain network connectivity patterns using novel imaging and analytical techniques may provide additional insights into PTH disease state and therefore inform effective treatment strategies.

Understanding Traumatic Brain Injury in Females: A State-of-the-Art Summary and Future Directions

In this report, we identify existing issues and challenges related to research on traumatic brain injury (TBI) in females and provide future directions for research. In 2017, the National Institutes of Health, in partnership with the Center for Neuroscience and Regenerative Medicine and the Defense and Veterans Brain Injury Center, hosted a workshop that focused on the unique challenges facing researchers, clinicians, patients, and other stakeholders regarding TBI in women. The goal of this "Understanding TBI in Women" workshop was to bring together researchers and clinicians to identify knowledge gaps, best practices, and target populations in research on females and/or sex differences within the field of TBI. The workshop, and the current literature, clearly highlighted that females have been underrepresented in TBI studies and clinical trials and have often been excluded (or ovariectomized) in preclinical studies. Such an absence in research on females has led to an incomplete, and perhaps inaccurate, understanding of TBI in females. The presentations and discussions centered on the existing knowledge regarding sex differences in TBI research and how these differences could be incorporated in preclinical and clinical efforts going forward. Now, a little over 2 years later, we summarize the issues and state of the science that emerged from the "Understanding TBI in Women" workshop while incorporating updates where they exist. Overall, despite some progress, there remains an abundance of research focused on males and relatively little explicitly on females.

Blast in Context: The Neuropsychological and Neurocognitive Effects of Long-Term Occupational Exposure to Repeated Low-Level Explosives on Canadian Armed Forces' Breaching Instructors and Range Staff

Currently, there is strong interest within the military to better understand the effects of long-term occupational exposure to repeated low-level blast on health and performance. To gain traction on the chronic sequelae of blast, we focused on breaching—a tactical technique for gaining entry into closed/blocked spaces by placing explosives and maintaining a calculated safe distance from the detonation. Using a cross-sectional design, we compared the neuropsychological and neurocognitive profiles of breaching instructors and range staff to sex- and age-matched Canadian Armed Forces (CAF) controls. Univariate tests demonstrated that breaching was associated with greater post-concussive symptoms (Rivermead Post Concussion Symptoms Questionnaire) and lower levels of energy (RAND SF-36). In addition, breaching instructors and range staff were slower on a test that requires moving and thinking simultaneously (i.e., cognitive-motor integration). Next, using a multivariate approach, we explored the impact of other possible sources of injury, including concussion and prior war-zone deployment on the same outcomes. Concussion history was associated with higher post-concussive scores and musculoskeletal problems, whereas deployment was associated with higher post-concussive scores, but lower energy and greater PTSD symptomatology (using PCL-5). Our results indicate that although breaching, concussion, and deployment were similarly correlated with greater post-concussive symptoms, concussion history appears to be uniquely associated with altered musculoskeletal function, whereas deployment history appears to be uniquely associated with lower energy and risk of PTSD. We argue that the broader injury context must, therefore, be considered when studying the impact of repetitive low-level explosives on health and performance in military members.

Characteristics and Impact of U.S. Military Blast-Related Mild Traumatic Brain Injury: A Systematic Review

As a result of armed conflict, head trauma from exposure to blasts is an increasing critical health issue, particularly among military service members. Whilst numerous studies examined the burden of blast-related brain injuries on service members', few systematic reviews have been published. This work provides a comprehensive summary of the evidence on blast-related mild traumatic brain injury (mTBI) burden in active U.S. military service members and inactive Veterans, describing characteristics and outcomes. Records published up to April 2017 were identified through a search of PubMed, Web of Science, Scopus, Ovid MEDLINE, and Cochrane Library. Records-based and original research reporting on U.S. military service members and Veterans with mild blast TBI were included. Data on subject characteristics, exposure, diagnostic criterion, and outcomes were extracted from included studies using a standardized extraction form and were presented narratively. Of the 2,290 references identified by the search, 106 studies with a total of 37,515 participants met inclusion criteria for blast-related mTBI. All but nine studies were based out of military or Veteran medical facilities. Unsurprisingly, men were over-represented (75–100%). The criteria used to define blast-related mTBI were consistent; however, the methodology used to ascertain whether individuals met those criteria for diagnosis were inconsistent. The diagnosis, most prevalent among the Army, heavily relied on self-reported histories. Commonly reported adverse outcomes included hearing disturbances and headaches. The most frequently associated comorbidities were post-traumatic stress disorder, depression, anxiety, sleep disorders, attention disorders, and cognitive disorders. The primary objective of this review was to provide a summary of descriptive data on blast-related mTBI in a U.S. military population. Low standardization of the methods for reaching diagnosis and problems in the study reporting emphasize the importance to collect high-quality data to fill knowledge gaps pertaining to blast-related mTBI.

Blast exposure predisposes the brain to increased neurological deficits in a model of blast plus blunt traumatic brain injury

Soldiers are often exposed to more than one traumatic brain injury (TBI) over the course of their service. In recent years, more attention has been drawn to the increased risk of neurological deficits caused by the 'blast plus' polytrauma, which typically is a blast trauma combined with other forms of TBI. In this study, we investigated the behavioral and neuronal deficits resulting from a blast plus injury involving a mild-moderate blast followed by a mild blunt trauma using the fluid percussion injury model. We identified that the blast injury predisposed the brain to increased cognitive deficits, chronic ventricular enlargement, increased neurodegeneration at acute time points and chronic neuronal loss. Interestingly, a single blast and single blunt injury differed in their onset and manifestation of cognitive and regional neuronal loss. We also identified the presence of cleaved RIP1 from caspase 8 mediated apoptosis in the blunt injury while the blast injury did not activate immediate apoptosis but led to decreased hilar neuronal survival over time.

Blast concussion and posttraumatic stress as predictors of postcombat neuropsychological functioning in OEF/OIF/OND veterans

OBJECTIVES

Many combat veterans exhibit cognitive limitations of uncertain origin. In this study, we examined factors that predict cognitive functioning by considering effects of blast-related concussion (BRC), non-blast-related concussion (NBRC), and posttraumatic stress disorder (PTSD) symptoms. Analyses specifically tested whether (a) BRC and NBRC were distinct in their prediction of cognitive performance; (b) a dose-response relationship existed between recurrent concussion (BRC and NBRC) and cognitive impairment; and (c) PTSD symptoms mediated the relationship between BRC and cognitive performance.

METHOD

Two hundred eighty veterans with combat zone deployment histories completed semistructured clinical interviews to define BRC and NBRC histories, current and past mental health disorders, and dimensional ratings of PTSD symptomatology. Participants were also administered a number of neuropsychological measures to appraise cognitive functioning.

RESULTS

A structural equation model (SEM) suggested that BRC and NBRC were not distinct in their prediction of cognitive performance, and there was no evidence that recurrent concussion (blast or nonblast) was directly associated with cognitive performance. BRC was significantly associated with PTSD symptoms (r = .24), PTSD symptoms were significantly associated with cognitive performance in the SEM (r = -.27), and PTSD symptoms significantly mediated the link between BRC and cognitive performance (p = .03).

CONCLUSIONS

These results suggest that concussion history fails to directly contribute to cognitive performance, regardless of mechanism (blast or nonblast) and recurrence. BRC is nonetheless unique in its contribution to PTSD and PTSD-related cognitive deficits. Results support interventions specific to PTSD management in the interest of promoting neuropsychological functioning among war veterans. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Neurocognitive Performance Deficits Related to Immediate and Acute Blast Overpressure Exposure

Addressing the concerns surrounding blast injury for the military community is a pressing matter. Specifically, sub-concussive blast effects, or those blast effects which do not yield a medical diagnosis but can result in symptom reporting and negative self-reported outcomes, are becoming increasingly important. This work evaluates explosive blast overpressure and impulse effects at the sub-concussive level on neurocognitive performance assessed with the Defense Automated Neurobehavioral Assessment (DANA) across seven breacher training courses conducted by the US Military. The results reported here come from 202 healthy, male military volunteer participants. Findings indicate that the neurocognitive task appearing most sensitive to identifying performance change is the DANA Procedural Reaction Time (PRT) subtask which may involve a sufficient level of challenge to reliably detect a small, transient cognitive impairment among a healthy undiagnosed population. The blast characteristic that was consistently associated with performance change was peak overpressure. Overall, this study provides evidence that increasing blast overpressure, defined as peak overpressure experienced in a training day, can lead to transient degradations in neurocognitive performance as seen on the DANA PRT subtask, which may generalize to other capabilities.

Outcomes Associated With Blast Versus Nonblast-Related Traumatic Brain Injury in US Military Service Members and Veterans: A Systematic Review

OBJECTIVES

To systematically review the literature on comparative clinical and functional outcomes following blast-related versus nonblast-related traumatic brain injury (TBI) among US service members and Veterans.

DESIGN

MEDLINE search (January 2001 to June 2016) supplemented with hand search of reference lists and input from peer reviewers.

RESULTS

Thirty-one studies (in 33 articles) reported on health outcomes; only 2 were rated low risk of bias. There was variation in outcomes reported and methods of assessment. Blast and nonblast TBI groups had similar rates of depression, sleep disorders, alcohol misuse, vision loss, vestibular dysfunction, and functional status. Comparative outcomes were inconsistent with regard to posttraumatic stress disorder diagnosis or symptoms, headache, hearing loss, and neurocognitive function. Mortality, burn, limb loss, and quality of life were each reported in few studies, most with small sample sizes. Only 4 studies reported outcomes by blast injury mechanism.

CONCLUSIONS

Most clinical and functional outcomes appeared comparable in military service members and Veterans with TBI, regardless of blast exposure. Inconsistent findings and limited outcomes reporting indicate that more research is needed to determine whether there is a distinct pattern of impairments and comorbidities associated with blast-related TBI.

Blast-Exposed Veterans With Mild Traumatic Brain Injury Show Greater Frontal Cortical Thinning and Poorer Executive Functioning

Objective: Blast exposure (BE) and mild traumatic brain injury (mTBI) have been independently linked to pathological brain changes. However, the combined effects of BE and mTBI on brain structure have yet to be characterized. Therefore, we investigated whether regional differences in cortical thickness exist between mTBI Veterans with and without BE while on deployment. We also examined whether cortical thickness (CT) and cognitive performance differed among mTBI Veterans with low vs. high levels of cumulative BE. Methods: 80 Veterans with mTBI underwent neuroimaging and completed neuropsychological testing and self-report symptom rating scales. Analyses of covariance (ANCOVA) were used to compare blast-exposed Veterans (mTBI+BE, n = 51) to those without BE (mTBI-BE, n = 29) on CT of frontal and temporal a priori regions of interest (ROIs). Next, multiple regression analyses were used to examine whether CT and performance on an executive functions composite differed among mTBI Veterans with low (mTBI+BE Low, n = 22) vs. high (mTBI+BE High, n = 26) levels of cumulative BE. Results: Adjusting for age, numer of TBIs, and PTSD symptoms, the mTBI+BE group showed significant cortical thinning in frontal regions (i.e., left orbitofrontal cortex [p = 0.045], left middle frontal gyrus [p = 0.023], and right inferior frontal gyrus [p = 0.034]) compared to the mTBI-BE group. No significant group differences in CT were observed for temporal regions (p's > 0.05). Multiple regression analyses revealed a significant cumulative BE × CT interaction for the left orbitofrontal cortex (p = 0.001) and left middle frontal gyrus (p = 0.020); reduced CT was associated with worse cognitive performance in the mTBI+BE High group but not the mTBI+BE Low group. Conclusions: Findings show that Veterans with mTBI and BE may be at risk for cortical thinning post-deployment. Moreover, our results demonstrate that reductions in CT are associated with worse executive functioning among Veterans with high levels of cumulative BE. Future longitudinal studies are needed to determine whether BE exacerbates mTBI-related cortical thinning or independently negatively influences gray matter structure.

Blast-induced "PTSD": Evidence from an animal model

A striking observation among veterans returning from the recent conflicts in Iraq and Afghanistan has been the co-occurrence of blast-related mild traumatic brain injury (mTBI) and post-traumatic stress disorder (PTSD). PTSD and mTBI might coexist due to additive effects of independent psychological and physical traumas experienced in a war zone. Alternatively blast injury might induce PTSD-related traits or damage brain structures that mediate responses to psychological stressors, increasing the likelihood that PTSD will develop following a subsequent psychological stressor. Rats exposed to repetitive low-level blasts consisting of three 74.5 kPa exposures delivered once daily for three consecutive days develop a variety of anxiety and PTSD-related behavioral traits that are present for at least 9 months after blast exposure. A single predator scent challenge delivered 8 months after the last blast exposure induces additional anxiety-related changes that are still present 45 days later. Because the blast injuries occur under general anesthesia, it appears that blast exposure in the absence of a psychological stressor can induce chronic PTSD-related traits. The reaction to a predator scent challenge delivered many months after blast exposure suggests that blast exposure in addition sensitizes the brain to react abnormally to subsequent psychological stressors. The development of PTSD-related behavioral traits in the absence of a psychological stressor suggests the existence of blast-induced "PTSD". Findings that PTSD-related behavioral traits can be reversed by BCI-838, a group II metabotropic glutamate receptor antagonist offers insight into pathogenesis and possible treatment options for blast-related brain injury. This article is part of the Special Issue entitled "Novel Treatments for Traumatic Brain Injury".

Longitudinal changes in neuroimaging and neuropsychiatric status of post-deployment veterans: a CENC pilot study

PRIMARY OBJECTIVE

The purpose of this study was to evaluate preliminary data on longitudinal changes in psychiatric, neurobehavioural, and neuroimaging findings in Iraq and Afghanistan combat veterans following blast exposure.

RESEARCH DESIGN

Longitudinal observational analysis.

METHODS AND PROCEDURES

Participants were invited to participate in two research projects approximately 7 years apart. For each project, veterans completed the Structured Clinical Interview for DSM-IV Disorders and/or the Clinician-Administered PTSD Scale, Neurobehavioral Symptom Inventory, and magnetic resonance imaging (MRI).

MAIN OUTCOMES AND RESULTS

Chi-squared tests indicated no significant changes in current psychiatric diagnoses, traumatic brain injury (TBI) history, or blast exposure history between assessment visits. Wilcoxon signed-rank tests indicated significant increases in median neurobehavioural symptoms, total number of white matter hyperintensities (WMH), and total WMH volume between assessment visits. Spearman rank correlations indicated no significant associations between change in psychiatric diagnoses, TBI history, blast exposure history, or neurobehavioural symptoms and change in WMH.

CONCLUSION

MRI WMH changes were not associated with changes in psychiatric diagnoses or symptom burden, but were associated with severity of blast exposure. Future, larger studies might further evaluate presence and aetiology of long-term neuropsychiatric symptoms and MRI findings in blast-exposed populations.

Unique Aspects of Traumatic Brain Injury in Military and Veteran Populations

Traumatic brain injury (TBI), in particular mild TBI (mTBI), is a relatively common injury experienced by service members across both deployed and nondeployed environments. Although many of the principles and practices used by civilian health care providers for identifying and treating this injury apply to military settings, there are unique factors that impact mTBI-related care in service members and Veterans. This article reviews several of these factors, including the epidemiology of TBI in the military/Veteran population, the influence of military culture on this condition, and identification and treatment of mTBI in the war zone.

Impact & Blast Traumatic Brain Injury: Implications for Therapy

Traumatic brain injury (TBI) is one of the most frequent causes of combat casualties in Operations Iraqi Freedom (OIF), Enduring Freedom (OEF), and New Dawn (OND). Although less common than combat-related blast exposure, there have been significant numbers of blast injuries in civilian populations in the United States. Current United States Department of Defense (DoD) ICD-9 derived diagnoses of TBI in the DoD Health Care System show that, for 2016, severe and moderate TBIs accounted for just 0.7% and 12.9%, respectively, of the total of 13,634 brain injuries, while mild TBIs (mTBIs) accounted for 86% of the total. Although there is a report that there are differences in the frequency of long-term complications in mTBI between blast and non-blast TBIs, clinical presentation is classified by severity score rather than mechanism because severity scoring is associated with prognosis in clinical practice. Blast TBI (bTBI) is unique in its pathology and mechanism, but there is no treatment specific for bTBIs-these patients are treated similarly to TBIs in general and therapy is tailored on an individual basis. Currently there is no neuroprotective drug recommended by the clinical guidelines based on evidence.

Diminished supraspinal pain modulation in patients with mild traumatic brain injury

Background

Chronic pain conditions are highly prevalent in patients with mild traumatic brain injury. Supraspinal diffuse axonal injury is known to dissociate brain functional connectivity in these patients. The effect of this dissociated state on supraspinal pain network is largely unknown. A functional magnetic resonance imaging study was conducted to compare the supraspinal pain network in patients with mild traumatic brain injury to the gender and age-matched healthy controls with the hypothesis that the functional connectivities of the medial prefrontal cortices, a supraspinal pain modulatory region to other pain-related sensory discriminatory and affective regions in the mild traumatic brain injury subjects are significantly reduced in comparison to healthy controls.

Results

The mild traumatic brain injury group (N = 15) demonstrated significantly (P < 0.01, cluster threshold > 150 voxels) less activities in the thalamus, pons, anterior cingulate cortex, insula, dorsolateral prefrontal cortex, and medial prefrontal cortices than the healthy control group (N = 15). Granger Causality Analyses (GCA) indicated while the left medial prefrontal cortices of the healthy control group cast a noticeable degree of outward (to affect) causality inference to multiple pain processing related regions, this outward inference pattern was not observed in the mild traumatic brain injury group. On the other hand, only patients’ bilateral anterior cingulate cortex received multiple inward (to be affected) causality inferences from regions including the primary and secondary somatosensory cortices and the inferior parietal lobe. Resting state functional connectivity analyses indicated that the medial prefrontal cortices of the mild traumatic brain injury group demonstrated a significantly (P < 0.01, F = 3.6, cluster size > 150 voxels) higher degree of functional connectivity to the inferior parietal lobe, premotor and secondary somatosensory cortex than the controls. Conversely, the anterior cingulate cortex of the healthy group demonstrated significantly (P < 0.01, F = 3.84, cluster size > 150 voxels) less degree of functional connectivities to the inferior parietal lobe and secondary somatosensory cortex than their mild traumatic brain injury counterparts.

Conclusions

In short, the current study demonstrates that patients with mild traumatic brain injury and headaches appear to have an altered state of supraspinal modulatory and affective functions related to pain perception.

Female Service Members and Symptom Reporting after Combat and Non-Combat-Related Mild Traumatic Brain Injury

Females are often excluded from military-related mild traumatic brain injury (mTBI) research because of its relatively low prevalence in this population. The purpose of this study was to focus on outcome from mTBI in female service members, compared with males. Participants were 172 United States military service members selected from a larger sample that had sustained an mTBI, and were evaluated within 24 months of injury (Age: mean = 28.9, SD = 8.1) at one of six military medical centers. Eighty-six women were matched to 86 men on nine key variables: TBI severity, mechanism of injury, bodily injury severity, days post-injury, age, number of deployments, theater where wounded, branch of service, and rank. Participants completed the Neurobehavioral Symptom Inventory (NSI) and the Posttraumatic Stress Disorder Checklist (PCL-C). There were no meaningful gender differences across all demographic and injury-related variables (p > 0.05). There were significant group differences and medium effect sizes for the NSI total score and all four NSI cluster scores. Symptoms most affected related to nausea, sensitivity to light, change in taste/smell, change in appetite, fatigue, and poor sleep. There were significant group differences and small-medium effect sizes for the PCL-C total score and two of the three PCL-C cluster scores. Symptoms most affected related to poor concentration, trouble remembering a stressful event, and disturbing memories/thoughts/images. Females consistently experienced more symptoms than males. As females become more active in combat-related deployments, it is critical that future studies place more emphasis on this important military population.

Assessing Quantitative Changes in Intrinsic Thalamic Networks in Blast and Nonblast Mild Traumatic Brain Injury: Implications for Mechanisms of Injury

In the global war on terror, the increased use of improvised explosive devices has resulted in increased incidence of blast-related mild traumatic brain injury (mTBI). Diagnosing mTBI is both challenging and controversial due to heterogeneity of injury location, trauma intensity, transient symptoms, and absence of focal biomarkers on standard clinical imaging modalities. The goal of this study is to identify a brain biomarker that is sensitive to mTBI injury. Research suggests the thalamus may be sensitive to changes induced by mTBI. A significant number of connections to and from various brain regions converge at the thalamus. In addition, the thalamus is involved in information processing, integration, and regulation of specific behaviors and mood. In this study, changes in task-free thalamic networks as quantified by graph theory measures in mTBI blast (N = 186), mTBI nonblast (N = 80), and controls (N = 21) were compared. Results show that the blast mTBI group had significant hyper-connectivity compared with the controls and nonblast mTBI group. However, after controlling for post-traumatic stress symptoms (PTSS), the blast mTBI group was not different from the controls, but the nonblast mTBI group showed significant hypo-connectivity. The results suggest that there are differences in the mechanisms of injury related to mTBI as reflected in the architecture of the thalamic networks. However, the effect of PTSS and its relationship to mTBI is difficult to distinguish and warrants more research.

Comparing the Neuropsychological Test Performance of Operation Enduring Freedom/Operation Iraqi Freedom (OEF/OIF) Veterans with and without Blast Exposure, Mild Traumatic Brain Injury, and Posttraumatic Stress Symptoms

To compare neuropsychological test performance of Veterans with and without mild traumatic brain injury (MTBI), blast exposure, and posttraumatic stress disorder (PTSD) symptoms. We compared the neuropsychological test performance of 49 Operation Enduring Freedom/Operation Iraqi Freedom (OEF/OIF) Veterans diagnosed with MTBI resulting from combat blast-exposure to that of 20 blast-exposed OEF/OIF Veterans without history of MTBI, 23 OEF/OIF Veterans with no blast exposure or MTBI history, and 40 matched civilian controls. Comparison of neuropsychological test performance across all four participant groups showed a complex pattern of mixed significant and mostly nonsignificant results, with omnibus tests significant for measures of attention, spatial abilities, and executive function. The most consistent pattern was the absence of significant differences between blast-exposed Veterans with MTBI history and blast-exposed Veterans without MTBI history. When blast-exposed Veteran groups with and without MTBI history were aggregated and compared to non-blast-exposed Veterans, there were significant differences for some measures of learning and memory, spatial abilities, and executive function. However, covariation for severity of PTSD symptoms eliminated all significant omnibus neuropsychological differences between Veteran groups. Our results suggest that, although some mild neurocognitive effects were associated with blast exposure, these neurocognitive effects might be better explained by PTSD symptom severity rather than blast exposure or MTBI history alone.

No Significant Acute and Subacute Differences between Blast and Blunt Concussions across Multiple Neurocognitive Measures and Symptoms in Deployed Soldiers

Seventy-one deployed U.S. Army soldiers who presented for concussion care due to either blast or blunt mechanisms within 72 h of injury were assessed using the Military Acute Concussion Evaluation, the Automated Neuropsychological Assessment Metrics (ANAM), traditional neuropsychological tests, and health status questionnaires. Follow-up ANAM testing was performed 10 d after initial testing (±5 d). Twenty-one soldiers were excluded: two for poor effort and 19 who had combined blast/blunt injuries. Of the remaining 50 male participants, 34 had blast injuries and 16 had blunt injuries. There were no statistically significant differences between blast injury and blunt injury participants in demographic, physical, or psychological health factors, concussive symptoms, or automated and traditional neurocognitive testing scores within 72 h post-injury. In addition, follow-up ANAM scores up to 15 d post-injury were not significantly different (available on 21 blast-injured and 13 blunt-injured subjects). Pre-injury baseline ANAM scores were compared where available, and revealed no statistically significant differences between 22 blast injury and eight blunt injury participants. These findings suggest there are no significant differences between mechanisms of injury during both the acute and subacute periods in neurobehavioral concussion sequelae while deployed in a combat environment. The current study supports the use of sports/mechanical concussion models for early concussion management in the deployed setting and exploration of variability in potential long-term outcomes.

Cognitive changes and dementia risk after traumatic brain injury: implications for aging military personnel

Traumatic brain injury (TBI) is recognized as an important risk factor for the long-term cognitive health of military personnel, particularly in light of growing evidence that TBI increases risk for Alzheimer's disease and other dementias. In this article, we review the neurocognitive and neuropathologic changes after TBI with particular focus on the potential risk for cognitive decline across the life span in military service members. Implications for monitoring and surveillance of cognition in the aging military population are discussed. Additional studies are needed to clarify the factors that increase risk for later life cognitive decline, define the mechanistic link between these factors and dementia, and provide empirically supported interventions to mitigate the impact of TBI on cognition across the life span.

Effects of low-level blast exposure on the nervous system: is there really a controversy?

High-pressure blast waves can cause extensive CNS injury in human beings. However, in combat settings, such as Iraq and Afghanistan, lower level exposures associated with mild traumatic brain injury (mTBI) or subclinical exposure have been much more common. Yet controversy exists concerning what traits can be attributed to low-level blast, in large part due to the difficulty of distinguishing blast-related mTBI from post-traumatic stress disorder (PTSD). We describe how TBI is defined in human beings and the problems posed in using current definitions to recognize blast-related mTBI. We next consider the problem of applying definitions of human mTBI to animal models, in particular that TBI severity in human beings is defined in relation to alteration of consciousness at the time of injury, which typically cannot be assessed in animals. However, based on outcome assessments, a condition of "low-level" blast exposure can be defined in animals that likely approximates human mTBI or subclinical exposure. We review blast injury modeling in animals noting that inconsistencies in experimental approach have contributed to uncertainty over the effects of low-level blast. Yet, animal studies show that low-level blast pressure waves are transmitted to the brain. In brain, low-level blast exposures cause behavioral, biochemical, pathological, and physiological effects on the nervous system including the induction of PTSD-related behavioral traits in the absence of a psychological stressor. We review the relationship of blast exposure to chronic neurodegenerative diseases noting the paradoxical lowering of Abeta by blast, which along with other observations suggest that blast-related TBI is pathophysiologically distinct from non-blast TBI. Human neuroimaging studies show that blast-related mTBI is associated with a variety of chronic effects that are unlikely to be explained by co-morbid PTSD. We conclude that abundant evidence supports low-level blast as having long-term effects on the nervous system.

Functional magnetic resonance imaging of mild traumatic brain injury

Functional magnetic resonance imaging (fMRI) offers great promise for elucidating the neuropathology associated with a single or repetitive mild traumatic brain injury (mTBI). The current review discusses the physiological underpinnings of the blood-oxygen level dependent response and how trauma affects the signal. Methodological challenges associated with fMRI data analyses are considered next, followed by a review of current mTBI findings. The majority of evoked studies have examined working memory and attentional functioning, with results suggesting a complex relationship between cognitive load/attentional demand and neuronal activation. Researchers have more recently investigated how brain trauma affects functional connectivity, and the benefits/drawbacks of evoked and functional connectivity studies are also discussed. The review concludes by discussing the major clinical challenges associated with fMRI studies of brain-injured patients, including patient heterogeneity and variations in scan-time post-injury. We conclude that the fMRI signal represents a complex filter through which researchers can measure the physiological correlates of concussive symptoms, an important goal for the burgeoning field of mTBI research.

Deployment-related mild traumatic brain injury, mental health problems, and post-concussive symptoms in Canadian Armed Forces personnel

BACKGROUND

Up to 20% of US military personnel deployed to Iraq or Afghanistan experience mild traumatic brain injury (mTBI) while deployed; up to one-third will experience persistent post-concussive symptoms (PCS). The objective of this study was to examine the epidemiology of deployment-related mTBI and its relationship to PCS and mental health problems (MHPs) in Canadian Armed Forces (CAF) personnel.

METHODS

Participants were 16153 personnel who underwent post-deployment screening (median =136 days after return) following deployment in support of the mission in Afghanistan from 2009 - 2012. The screening questionnaire assessed mTBI and other injuries while deployed, using the Brief Traumatic Brain Injury Screening Tool. Current MHPs and PCS were assessed using items from the Patient Health Questionnaire, the Patient Checklist for PTSD, and the Cognitive Failures Questionnaire. Log-binomial regression explored the association of mTBI, other injuries, and MHPs with PCS, using the presence of 3 or more of 7 PCS as the outcome. Results are expressed as adjusted prevalence ratios (PR).

RESULTS

mTBI while deployed was reported in 843 respondents (5.2%). Less severe forms of mTBI (associated only with having been dazed or confused or having "seen stars") predominated. Blast was reported as a mechanism of injury in half of those with mTBI. Multiple PCS were present in 21% of those with less severe forms of mTBI and in 27% of those with more severe forms of mTBI (i.e., mTBI associated with loss of consciousness or post-traumatic amnesia). After adjustment for confounding, mTBI had no statistically significant association with PCS relative to non-TBI injury. In contrast, MHPs had a strong association with reporting 3 or more PCS (adjusted prevalence ratio (PR) =7.77).

CONCLUSION

Deployment-related mTBI prevalence was lower than in many US reports; most of those who had had mTBI were free of multiple PCS. PCS was strongly associated with MHPs but not with mTBI. Careful assessment of MHPs is essential in personnel with a history of combat-related mTBI and PCS.

Preliminary findings of cortical thickness abnormalities in blast injured service members and their relationship to clinical findings

Though cortical abnormalities have been demonstrated in moderate and severe traumatic brain injured (TBI) patients, there have been no studies examining cortical changes following blast related mild TBI (mTBI). The purpose of this study was to determine the effects and functional relevance of blast mTBI on cortical thickness in a small cohort of carefully screened blast injured US Service Members (SM). Twelve SM with mTBI acquired through blast injury were compared to 11 demographically matched control SM without TBI. Both mTBI and control participants were active duty and had completed a combat deployment. Subjects underwent MRI examination and the T1 weighted anatomic images were processed using the FreeSurfer suite of tools. Cortical thickness maps were compared between groups and examined for relationships with time since injury (TSI). Utilizing a large database of functional imaging results (BrainMap), significant regions of interest (ROI) were used to determine the behavioral profiles most consistently associated with the specific ROI. In addition, clinical variables were examined as part of post-hoc analysis of functional relevance. Group comparisons controlling for age demonstrated several significant clusters of cortical thinning for the blast injured SM. After multiple comparisons correction (False Discovery Rate (FDR)), two left hemisphere clusters remained significant (left superior temporal (STG) and frontal (SFG) gyri). No clusters were significantly correlated with TSI after FDR correction. Behavioral analysis for the STG and SFG clusters demonstrated three significant behavioral/cognitive sub-domains, each associated with audition and language. Blast injured SMs demonstrated distinct areas of cortical thinning in the STG and SFG. These areas have been previously shown to be associated with audition and language. Post-hoc analyses of clinical records demonstrated significant abnormal audiology reports for the blast injured SM suggesting that the thinning in these ROIs might be related to injury to the external auditory system rather than direct injury to the brain from the blast. It is clear that additional replication is needed in much larger cohorts. Importantly, the combination of imaging tools and methods in this study successfully demonstrated the potential to define unique ROIs and functional correlates that can be used to design future studies.

The Boston Assessment of Traumatic Brain Injury-Lifetime (BAT-L) semistructured interview: evidence of research utility and validity

OBJECTIVE

Report the prevalence of lifetime and military-related traumatic brain injuries (TBIs) in Operation Enduring Freedom and Operation Iraqi Freedom (OEF/OIF) veterans and validate the Boston Assessment of TBI-Lifetime (BAT-L).

SETTING

The BAT-L is the first validated, postcombat, semistructured clinical interview to characterize head injuries and diagnose TBIs throughout the life span.

PARTICIPANTS

Community-dwelling convenience sample of 131 OEF/OIF veterans.

DESIGN

TBI criteria (alteration of mental status, posttraumatic amnesia, and loss of consciousness) were evaluated for all possible TBIs, including a novel evaluation of blast exposure.

MAIN MEASURES

BAT-L, Ohio State University TBI Identification Method (OSU-TBI-ID).

RESULTS

About 67% of veterans incurred a TBI in their lifetime. Almost 35% of veterans experienced at least 1 military-related TBI; all were mild in severity, 40% of them were due to blast, 50% were due to some other (ie, blunt) mechanism, and 10% were due to both types of injuries. Predeployment TBIs were frequent (45% of veterans). There was strong correspondence between the BAT-L and the OSU-TBI-ID (Cohen κ = 0.89; Kendall τ-b = 0.95). Interrater reliability of the BAT-L was strong (κs >0.80).

CONCLUSIONS

The BAT-L is a valid instrument with which to assess TBI across a service member's lifetime and captures the varied and complex nature of brain injuries across OEF/OIF veterans' life span.

Perfusion deficits in patients with mild traumatic brain injury characterized by dynamic susceptibility contrast MRI

Perfusion deficits in patients with mild traumatic brain injury (TBI) from a military population were characterized by dynamic susceptibility contrast perfusion imaging. Relative cerebral blood flow (rCBF) was calculated by a model-independent deconvolution approach from the tracer concentration curves following a bolus injection of gadolinium diethylenetriaminepentaacetate (Gd-DTPA) using both manually and automatically selected arterial input functions (AIFs). Linear regression analysis of the mean values of rCBF from selected regions of interest showed a very good agreement between the two approaches, with a regression coefficient of R = 0.88 and a slope of 0.88. The Bland-Altman plot also illustrated the good agreement between the two approaches, with a mean difference of 0.6 ± 12.4 mL/100 g/min. Voxelwise analysis of rCBF maps from both approaches demonstrated multiple clusters of decreased perfusion (p < 0.01) in the cerebellum, cuneus, cingulate and temporal gyrus in the group with mild TBI relative to the controls. MRI perfusion deficits in the cerebellum and anterior cingulate also correlated (p < 0.01) with neurocognitive results, including the mean reaction time in the Automated Neuropsychological Assessment Metrics and commission error and detection T-scores in the Continuous Performance Test, as well as neurobehavioral scores in the Post-traumatic Stress Disorder Checklist-Civilian Version. In conclusion, rCBF calculated using AIFs selected from an automated approach demonstrated a good agreement with the corresponding results using manually selected AIFs. Group analysis of patients with mild TBI from a military population demonstrated scattered perfusion deficits, which showed significant correlations with measures of verbal memory, speed of reaction time and self-report of stress symptoms.

Functional MRI in the investigation of blast-related traumatic brain injury

This review focuses on the application of functional magnetic resonance imaging (fMRI) to the investigation of blast-related traumatic brain injury (bTBI). Relatively little is known about the exact mechanisms of neurophysiological injury and pathological and functional sequelae of bTBI. Furthermore, in mild bTBI, standard anatomical imaging techniques (MRI and computed tomography) generally fail to show focal lesions and most of the symptoms present as subjective clinical functional deficits. Therefore, an objective test of brain functionality has great potential to aid in patient diagnosis and provide a sensitive measurement to monitor disease progression and treatment. The goal of this review is to highlight the relevant body of blast-related TBI literature and present suggestions and considerations in the development of fMRI studies for the investigation of bTBI. The review begins with a summary of recent bTBI publications followed by discussions of various elements of blast-related injury. Brief reviews of some fMRI techniques that focus on mental processes commonly disrupted by bTBI, including working memory, selective attention, and emotional processing, are presented in addition to a short review of resting state fMRI. Potential strengths and weaknesses of these approaches as regards bTBI are discussed. Finally, this review presents considerations that must be made when designing fMRI studies for bTBI populations, given the heterogeneous nature of bTBI and its high rate of comorbidity with other physical and psychological injuries.

Understanding and treating blast traumatic brain injury in the combat theater

OBJECTIVES

Blast injury is a frequent cause of traumatic brain injury (TBI) in the modern combat theater. We sought to explain the research and treatment associated with this injury.

METHODS

We reviewed literature on the prevalence of blast TBI (bTBI), blast injury mechanisms, research, and perspectives on the neurosurgical experience treating bTBI.

RESULTS

A majority of combat-related casualties in recent wars are due to blast. A majority of survivors of blast injuries are diagnosed with TBI. Blast injury may induce changes in the brain not seen with non-blast-related mechanisms. However, long-term symptoms are not significantly different from non-blast mechanisms. Aggressive decompressive craniectomies are commonly performed in the combat theater.

DISCUSSION

Due to the prevalence and debilitating nature of bTBI, understanding injury mechanisms is crucial in treating the injury before symptoms become permanent. Treatment is currently limited to decompressive craniectomies, which are the most effective treatment for a relatively young and fit military population.