Bomb blast, mild traumatic brain injury and psychiatric morbidity: a review

Assessing neuro-systemic & behavioral components in the pathophysiology of blast-related brain injury

Among the U.S. military personnel, blast injury is among the leading causes of brain injury. During the past decade, it has become apparent that even blast injury as a form of mild traumatic brain injury (mTBI) may lead to multiple different adverse outcomes, such as neuropsychiatric symptoms and long-term cognitive disability. Blast injury is characterized by blast overpressure, blast duration, and blast impulse. While the blast injuries of a victim close to the explosion will be severe, majority of victims are usually at a distance leading to milder form described as mild blast TBI (mbTBI). A major feature of mbTBI is its complex manifestation occurring in concert at different organ levels involving systemic, cerebral, neuronal, and neuropsychiatric responses; some of which are shared with other forms of brain trauma such as acute brain injury and other neuropsychiatric disorders such as post-traumatic stress disorder. The pathophysiology of blast injury exposure involves complex cascades of chronic psychological stress, autonomic dysfunction, and neuro/systemic inflammation. These factors render blast injury as an arduous challenge in terms of diagnosis and treatment as well as identification of sensitive and specific biomarkers distinguishing mTBI from other non-TBI pathologies and from neuropsychiatric disorders with similar symptoms. This is due to the “distinct” but shared and partially identified biochemical pathways and neuro-histopathological changes that might be linked to behavioral deficits observed. Taken together, this article aims to provide an overview of the current status of the cellular and pathological mechanisms involved in blast overpressure injury and argues for the urgent need to identify potential biomarkers that can hint at the different mechanisms involved.

Traumatic brain injury: oxidative stress and neuroprotection

SIGNIFICANCE

A vast amount of circumstantial evidence implicates high energy oxidants and oxidative stress as mediators of secondary damage associated with traumatic brain injury. The excessive production of reactive oxygen species due to excitotoxicity and exhaustion of the endogenous antioxidant system induces peroxidation of cellular and vascular structures, protein oxidation, cleavage of DNA, and inhibition of the mitochondrial electron transport chain.

RECENT ADVANCES

Different integrated responses exist in the brain to detect oxidative stress, which is controlled by several genes termed vitagens. Vitagens encode for cytoprotective heat shock proteins, and thioredoxin and sirtuins.

CRITICAL ISSUES AND FUTURE DIRECTIONS

This article discusses selected aspects of secondary brain injury after trauma and outlines key mechanisms associated with toxicity, oxidative stress, inflammation, and necrosis. Finally, this review discusses the role of different oxidants and presents potential clinically relevant molecular targets that could be harnessed to treat secondary injury associated with brain trauma.

Blast-related traumatic brain injury

A bomb blast may cause the full severity range of traumatic brain injury (TBI), from mild concussion to severe, penetrating injury. The pathophysiology of blast-related TBI is distinctive, with injury magnitude dependent on several factors, including blast energy and distance from the blast epicentre. The prevalence of blast-related mild TBI in modern war zones has varied widely, but detection is optimised by battlefield assessment of concussion and follow-up screening of all personnel with potential concussive events. There is substantial overlap between post-concussive syndrome and post-traumatic stress disorder, and blast-related mild TBI seems to increase the risk of post-traumatic stress disorder. Post-concussive syndrome, post-traumatic stress disorder, and chronic pain are a clinical triad in this patient group. Persistent impairment after blast-related mild TBI might be largely attributable to psychological factors, although a causative link between repeated mild TBIs caused by blasts and chronic traumatic encephalopathy has not been established. The application of advanced neuroimaging and the identification of specific molecular biomarkers in serum for diagnosis and prognosis are rapidly advancing, and might help to further categorise these injuries.

Time-dependent changes of protein biomarker levels in the cerebrospinal fluid after blast traumatic brain injury

Time-dependent changes of protein biomarkers in the cerebrospinal fluid (CSF) can be used to identify the pathological processes in traumatic brain injury (TBI) as well as to follow the progression of the disease. We obtained CSF from a large animal model (swine) of blast-induced traumatic brain injury prior to and at 6, 24, 72 h, and 2 wk after a single exposure to blast overpressure, and determined changes in the CSF levels of neurofilament-heavy chain, neuron-specific enolase, brain-specific creatine kinase, glial fibrillary acidic protein, calcium-binding protein β (S100β), Claudin-5, vascular endothelial growth factor, and von Willebrand factor using reverse phase protein microarray. We detected biphasic temporal patterns in the CSF concentrations of all tested protein markers except S100β. The CSF levels of all markers were significantly increased 6 h after the injury compared to preinjury levels. Values were then decreased at 24 h, prior to a second increase in all markers but S100β at 72 h. At 2 wk postinjury, the CSF concentrations of all biomarkers were decreased once again; brain-specific creatine kinase, Claudin-5, von Willebrand factor, and S100β levels were no longer significantly higher than their preinjury values while neurofilament-heavy chain, neuron-specific enolase, vascular endothelial growth factor, and glial fibrillary acidic protein levels remained significantly elevated compared to baseline. Our findings implicate neuronal and glial cell damage, compromised vascular permeability, and inflammation in blast-induced traumatic brain injury, as well as demonstrate the value of determining the temporal pattern of biomarker changes that may be of diagnostic value.

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.

Effects of blast-induced neurotrauma on the nucleus accumbens

Blast-induced neurotrauma (BINT) leads to deterioration at the cellular level, with adverse cognitive and behavioral outcomes. The nucleus accumbens (NAC) plays an important role in reward, addiction, aggression, and fear pathways. To identify the molecular changes and pathways affected at an acute stage in the NAC, this study focused on a time course analysis to determine the effects of blast on neurochemical and apoptotic pathways. By using a rodent model of BINT, acute damage to the NAC was assessed by proton magnetic resonance spectroscopy (¹H-MRS), high-performance liquid chromatography, immunohistochemistry, and Western blotting. The results demonstrated ongoing neuroprotective effects from elevated levels of Bcl-2, an antiapoptotic marker, at 24 hr and N-acetyl aspartate glutamate at 48 hr following blast exposure. Selective loss of serotonin levels at 24 hr, increased levels of inflammation (elevated glycerophosphocholine at 48 and 72 hr), and increased levels of glial fibrillary acidic protein were also observed at 24 and 48 hr, leading to disruptive energy status. Furthermore, active cell death was indicated by the increased levels of the apoptotic marker Bax, decreased actin levels, and signs excitotoxicity (glutamate/creatine). In addition, increased levels of caspase-3, an apoptotic marker, confirm active cell death in NAC. It is hypothesized that blast overpressure causes inflammation and neurochemical changes that trigger apoptosis in NAC. This cascade of events may lead to stress-related behavioral outcomes and psychiatric sequelae.

Sleep disturbances among soldiers with combat-related traumatic brain injury

BACKGROUND

Sleep complaints are common among patients with traumatic brain injury. Evaluation of this population is confounded by polypharmacy and comorbid disease, with few studies addressing combat-related injuries. The aim of this study was to assess the prevalence of sleep disorders among soldiers who sustained combat-related traumatic brain injury.

METHODS

The study design was a retrospective review of soldiers returning from combat with mild to moderate traumatic brain injury. All underwent comprehensive sleep evaluations. We determined the prevalence of sleep complaints and disorders in this population and assessed demographics, mechanism of injury, medication use, comorbid psychiatric disease, and polysomnographic findings to identify variables that correlated with the development of specific sleep disorders.

RESULTS

Of 116 consecutive patients, 96.6% were men (mean age, 31.1 ± 9.8 years; mean BMI, 27.8 ± 4.1 kg/m²), and 29.5% and 70.5% sustained blunt and blast injuries, respectively. Nearly all (97.4%) reported sleep complaints. Hypersomnia and sleep fragmentation were reported in 85.2% and 54.3%, respectively. Obstructive sleep apnea syndrome (OSAS) was found in 34.5%, and 55.2% had insomnia. Patients with blast injuries developed more anxiety (50.6% vs 20.0%, P = .002) and insomnia (63% vs 40%, P = .02), whereas patients with blunt trauma had significantly more OSAS (54.3% vs 25.9%, P = .003). In multivariate analysis, blunt trauma was a significant predictor of OSAS (OR, 3.09; 95% CI, 1.02-9.38; P = .047).

CONCLUSIONS

Sleep disruption is common following traumatic brain injury, and the majority of patients develop a chronic sleep disorder. It appears that sleep disturbances may be influenced by the mechanism of injury in those with combat-related traumatic brain injury, with blunt injury potentially predicting the development of OSAS.

Blast-induced neurotrauma leads to neurochemical changes and neuronal degeneration in the rat hippocampus

Blast-induced neurotrauma is a major concern because of the complex expression of neuropsychiatric disorders after exposure. Disruptions in neuronal function, proximal in time to blast exposure, may eventually contribute to the late emergence of clinical deficits. Using magic angle spinning ¹H MRS and a rodent model of blast-induced neurotrauma, we found acute (24-48 h) decreases in succinate, glutathione, glutamate, phosphorylethanolamine and γ-aminobutyric acid, no change in N-acetylaspartate and increased glycerophosphorylcholine, alterations consistent with mitochondrial distress, altered neurochemical transmission and increased membrane turnover. Increased levels of the apoptotic markers Bax and caspase-3 suggested active cell death, consistent with increased FluoroJade B staining in the hippocampus. Elevated levels of glial fibrillary acidic protein suggested ongoing inflammation without diffuse axonal injury measured by no change in β-amyloid precursor protein. In conclusion, blast-induced neurotrauma induces a metabolic cascade associated with neuronal loss in the hippocampus in the acute period following exposure.

Introduction to the brain imaging and behavior special issue on neuroimaging findings in mild traumatic brain injury

Contemporary neuroimaging methods and research findings in mild traumatic brain injury (mTBI) are reviewed in this special issue. Topics covered include structural and functional neuroimaging techniques with a particular emphasis on the most contemporary research involving magnetic resonance imaging (MRI). Future research directions as well as applied applications of using neuroimaging techniques to define biomarkers of brain injury are covered.

Posttraumatic stress disorder and traumatic brain injury in current military populations: a critical analysis

BACKGROUND

The use of unconventional weaponry combined with decreased mortality rates and servicemembers being exposed to intense ground combat during multiple deployments has increased the risk of servicemembers living with the consequences of traumatic brain injuries (TBI) and combat operational stress.

OBJECTIVE

The purpose of this article is to perform a critical analysis of the literature to identify current rates of comorbid posttraumatic stress disorder (PTSD) and TBI in military and veteran populations who have served in Iraq or Afghanistan and their combined effects on persistent postconcussive symptoms.

DESIGN

A search of the literature with military and veteran populations published after 2001 in Pubmed, OVID/Medline, Cochran Database, Embase, Scopus, CINAHL, and PsychInfo was conducted using keywords.

RESULTS

Twenty studies met inclusion criteria. The literature search yielded mixed results for rates of PTSD, TBI, and comorbid conditions.

CONCLUSIONS

There is some evidence that comorbid PTSD and TBI result in greater reports of postconcussive symptomology than either condition alone. Limitations include lack of consistency of measurements, sampling biases, and lack of experimental design, and these warrant further exploration. Future research is needed to decrease variability in study findings and elucidate relationships between these disorders and their effects on persistent postconcussive symptomology.

Chronic traumatic encephalopathy in an Iraqi war veteran with posttraumatic stress disorder who committed suicide

Following his discovery of chronic traumatic encephalopathy (CTE) in football players in 2002, Dr. Bennet Omalu hypothesized that posttraumatic stress disorder (PTSD) in military veterans may belong to the CTE spectrum of diseases. The CTE surveillance at the Brain Injury Research Institute was therefore expanded to include deceased military veterans diagnosed with PTSD. The authors report the case of a 27-year-old United States Marine Corps (USMC) Iraqi war veteran, an amphibious assault vehicle crewman, who committed suicide by hanging after two deployments to Fallujah and Ramadi. He experienced combat and was exposed to mortar blasts and improvised explosive device blasts less than 50 m away. Following his second deployment he developed a progressive history of cognitive impairment, impaired memory, behavioral and mood disorders, and alcohol abuse. Neuropsychiatric assessment revealed a diagnosis of PTSD with hyperarousal (irritability and insomnia) and numbing. He committed suicide approximately 8 months after his honorable discharge from the USMC. His brain at autopsy appeared grossly unremarkable except for congestive brain swelling. There was no atrophy or remote focal traumatic brain injury such as contusional necrosis or hemorrhage. Histochemical and immunohistochemical brain tissue analysis revealed CTE changes comprising multifocal, neocortical, and subcortical neurofibrillary tangles and neuritic threads (ranging from none, to sparse, to frequent) with the skip phenomenon, accentuated in the depths of sulci and in the frontal cortex. The subcortical white matter showed mild rarefaction, sparse perivascular and neuropil infiltration by histiocytes, and mild fibrillary astrogliosis. Apolipoprotein E genotype was 3/4. The authors report this case as a sentinel case of CTE in an Iraqi war veteran diagnosed with PTSD to possibly stimulate new lines of thought and research in the possible pathoetiology and pathogenesis of PTSD in military veterans as part of the CTE spectrum of diseases, and as chronic sequelae and outcomes of repetitive traumatic brain injuries.

Serum-based protein biomarkers in blast-induced traumatic brain injury spectrum disorder

The biological consequences of exposure to explosive blast are extremely complex. Serum protein biomarkers in blast-induced traumatic brain injury (bTBI) can aid in determining injury severity, monitoring progress, and predicting outcome. Exposure to blast results in varying degrees of physical injury. Explosive blast can also induce psychological stress that can contribute to or amplify the extent of physical damage. Given the complexity, scale of injury, and variety of symptoms, bTBI may be best described as a spectrum disorder. In this focused review, we summarize the status of serum protein biomarkers in bTBI in the context of the classification and pathological changes of other forms of TBI. Finally, we recommend specific and easily implementable measures to accelerate serum protein biomarker discovery and validation in bTBI.

Neuropsychological sequelae of PTSD and TBI following war deployment among OEF/OIF veterans

Posttraumatic stress disorder (PTSD) and mild traumatic brain injury (mTBI) are highly prevalent among Veterans of the conflicts in Iraq and Afghanistan. These conditions are associated with common and unique neuropsychological and neuroanatomical changes. This review synthesizes neuropsychological and neuroimaging studies for both of these disorders and studies examining their co-occurrence. Recommendations for future research, including use of combined neuropsychological and advanced neuroimaging techniques to study these disorders alone and in concert, are presented. It is clear from the dearth of literature that addiitonal studies are required to examine and understand the impact of specific factors on neurocognitive outcome. Of particular relevance are temporal relationships between PTSD and mTBI, risk and resilience factors associated with both disorders and their co-occurrence, and mTBI-specific factors such as time since injury and severity of injury, utilizing comprehensive, yet targeted cognitive tasks.

Neuropsychological and neuroimaging findings in traumatic brain injury and post-traumatic stress disorder

Advances in imaging technology, coupled with military personnel returning home from Iraq and Afghanistan with traumatic brain injury (TBI) and/or post-traumatic stress disorder (PTSD), have increased interest in the neuropsychology and neurobiology of these two conditions. There has been a particular focus on differential diagnosis. This paper provides an overview of findings regarding the neuropsychological and neurobiological underpinnings of TBI and for PTSD. A specific focus is on assessment using neuropsychological measures and imaging techniques. Challenges associated with the assessment of individuals with one or both conditions are also discussed. Although use of neuropsychological and neuroimaging test results may assist with diagnosis and treatment planning, further work is needed to identify objective biomarkers for each condition. Such advances would be expected to facilitate differential diagnosis and implementation of best treatment practices.

Effect of blast exposure on the brain structure and cognition in Macaca fascicularis

Blast injury to the brain is one of the major causes of death and can also significantly affect cognition and physical and psychological skills in survivors of blast. The complex mechanisms via which blast injury causes impairment of cognition and other symptoms are poorly understood. In this study, we investigated the effects of varying degrees of primary blast overpressure (BOP; 80 and 200 kPa) on the pathophysiological and magnetic resonance imaging (MRI) changes and neurocognitive performance as assessed by the monkey Cambridge Neuropsychological Test Automated Battery (mCANTAB) in non-human primates (NHP). The study aimed to examine the effects of neurobehavioral and histopathological changes in NHP. MRI and histopathology revealed ultrastructural changes in the brain, notably in the Purkinje neurons in the cerebellum and pyramidal neurons in the hippocampus, which were most vulnerable to the blast. The results correlated well with the behavioral changes and changes in motor coordination and working memory of the affected monkeys. In addition, there was white matter damage affecting myelinated axons, astrocytic hypertrophy, and increased aquaporin-4 (AQP-4) expression in astrocytes, suggesting cerebral edema. Increased apoptosis appeared to involve astrocytes and oligodendrocytes in the animals following blast exposure. The small sample size could have contributed to the non-significant outcome in cognitive performance post-blast and limited quantitative analyses. Nevertheless, the study has provided initial descriptive changes for establishing a primary BOP threshold for brain injury to serve as a useful platform for future investigations that aim to estimate brain injury potential and set safe limits of exposure.

Posttraumatic stress disorder in hospitalized terrorist bombing attack victims

BACKGROUND

Posttraumatic stress disorder (PTSD) is a psychiatric disorder that results from exposure to a traumatic event and consists of intrusive and unwanted recollections; avoidance followed by emotional withdrawal; and heightened physiologic arousal. Hospitalized victims of suicide bombing attacks (SBAs) are unique because of the circumstances and severity of their injuries, which could affect the occurrence and delay the recognition of PTSD. Our objectives were to evaluate the prevalence and severity of PTSD among hospitalized SBA victims and to assess variables of physical injury as risk factors for the development of PTSD.

METHODS

Forty-six hospitalized SBA victims were evaluated for PTSD using the PTSD symptom scale self-report questionnaire by phone. Demographic and medical data regarding the severity and type of injury and medical treatment were collected from medical files. Injury Severity Score was used to assess severity of physical injury.

RESULTS

Twenty-four of 46 (52.2%) hospitalized SBA victims developed PTSD. Presence of blast lung injury was significantly higher in the PTSD group compared with the non-PTSD group (37.5% versus 9.1%, respectively; p < 0.04). There was no significant difference in Injury Severity Score between PTSD and non-PTSD groups. Blast lung injury and intracranial injury were found to be positive predictors of PTSD (odds ratio, 125 and 25, respectively). No correlation was found between the length of stay, length of intensive care unit stay, or severity of physical injuries and the severity of PTSD.

CONCLUSIONS

Hospitalized victims of SBA are considerably vulnerable to develop PTSD. Victims should be monitored closely and treated in conjunction with their physical treatment. Blast lung injury and intracranial injury are predictors of PTSD.

Validation of the Abbreviated Westmead Post-traumatic Amnesia Scale: a brief measure to identify acute cognitive impairment in mild traumatic brain injury

OBJECTIVE

To validate the use of the Abbreviated Westmead Post-traumatic Amnesia Scale (A-WPTAS) in the assessment of acute cognitive impairment in mild traumatic brain injury (mTBI).

METHODS

Data previously collected from 82 mTBI and 88 control participants using the Revised Westmead Post-traumatic Amnesia Scale (R-WPTAS) was converted to A-WPTAS scores and pass/fail classifications were calculated for both scales.

RESULTS

The proportion of failures on the R-WPTAS and the A-WPTAS did not differ and a similar number of mTBIs were classified on each. For mTBIs the relationship between the independent memory test and a pass/fail classification was the same for both scales. Bivariate logistic regressions revealed that mTBIs, relative to controls, were around 8 times more likely to fail the assessment (R-WPTAS: 95% CI: 3.70-18.87; A-WPTAS: 95% CI: 3.70-20.14). As verbal learning improved the likelihood of failure was reduced. Greater education was associated with a decreased likelihood of failure. The relationship between education and a fail performance was not sustained when education was adjusted for the effect of age, prior mTBI, blood alcohol level, injury status, verbal learning, and morphine administration.

CONCLUSIONS

The A-WPTAS is a valid measure. The A-WPTAS may reduce the risk of failing to classify patients with mTBI by identifying and documenting acute cognitive impairment.