Effects of hours of sleep on ImPACT concussion testing: comparing baseline with postinjury scores

OBJECTIVE

The influence of sleep on baseline and postconcussion neurocognitive performance prior to Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) is poorly understood. Since ImPACT is widely used in youth sport to assess neurocognitive performance before and after head injury, it is important to delineate factors that affect testing performance. While some have reported correlations between fewer hours of sleep and lower scores on baseline tests, others have not observed any such associations. Therefore, the authors sought to compare the relationship between sleep and neurocognitive performance on ImPACT at both baseline and postinjury.

METHODS

The authors queried a database of 25,815 ImPACT tests taken from 2009 to 2019 by athletes aged 12-22 years. There were 11,564 baseline concussion tests and 7446 postinjury concussion ImPACT tests used in the analysis. Linear regression was used to model the effect of sleep on baseline and postconcussion ImPACT scores adjusting for sex, age, learning disability, attention-deficit/hyperactivity disorder, number of prior concussions, number of games missed, and strenuous exercise before testing.

RESULTS

Mean composite scores expectedly were all significantly lower in the post-head injury group compared with the baseline group. In the multivariable analysis, at baseline, hours of sleep significantly affected symptom scores (β = -1.050, 95% CI -1.187 to -0.9138; p < 0.0001). In the postinjury multivariable analysis, verbal memory (β = 0.4595, 95% CI 0.2080-0.7110; p = 0.0003), visual memory (β = 0.3111, 95% CI 0.04463-0.5777; p = 0.0221), impulse control (β = -0.2321, 95% CI -0.3581 to -0.1062; p = 0.0003), and symptom scores (β = -0.9168, 95% CI -1.259 to -0.5750; p < 0.0001) were all affected by hours of sleep.

CONCLUSIONS

Hours of sleep did not alter neurocognitive metrics at baseline but did have an impact on post-head injury metrics. These findings suggest that individuals may be able to compensate for lack of sleep at baseline but not immediately after concussion. Concussions may reduce cognitive reserve or detract from the brain's resources, making sleep even more important for proper neurocognitive functioning postconcussion. Future work will analyze the effects of sleep on postconcussion test performance.

Multidisciplinary care for patients with persistent symptoms following concussion: a systematic review

PURPOSE

To systematically characterize and assess the effectiveness of multidisciplinary care for patients with persistent post-concussion symptoms (PPCS).

MATERIALS AND METHODS

Only studies describing multidisciplinary treatment, defined as intervention provided by no less than 2 healthcare disciplines, each with independent scopes of practice, for patients with PPCS were considered.

RESULTS

A total of 8 of the 1357 studies identified were included. The studies were comprised of heterogenous patient populations, care delivery systems, healthcare providers, treatment approaches, and outcomes.

CONCLUSIONS

Findings suggest multidisciplinary care, using a needs-based approach with individual- or group-based interventions, may be more beneficial than usual care to; 1) immediately reduce concussion-related symptom complaints and improve mood and quality of life in adolescents following sports-related concussion (SRC) and, 2) may produce immediate and lasting improvements in symptom complaints of young, primarily female, adults following a non-SRC. Future studies should clearly describe the decision-making processes used to deliver care through a needs-based approach and prioritize the inclusion of objective, performance-based measures to assess outcomes.

Phenotyping Depression After Mild Traumatic Brain Injury: Evaluating the Impact of Multiple Injury, Gender, and Injury Context

The chronic mental health consequences of mild traumatic brain injury (TBI) are a leading cause of disability. This is surprising given the expectation of significant recovery after mild TBI, which suggests that other injury-related factors may contribute to long-term adverse outcomes. The objective of this study was to determine how number of prior injuries, gender, and environment/context of injury may contribute to depressive symptoms after mild TBI among deployed United States service members and veterans (SMVs). Data from the Long-term Impact of Military-Relevant Brain Injury Consortium Prospective Longitudinal Study was used to assess TBI injury characteristics and depression scores previously measured on the Patient Health Questionnaire-9 (PHQ-9) among a sample of 1456 deployed SMVs. Clinical diagnosis of mild TBI was defined via a multi-step process centered on a structured face-to-face interview. Logistical and linear regressions stratified by gender and environment of injury were used to model depressive symptoms controlling for sociodemographic and combat deployment covariates. Relative to controls with no history of mild TBI (n = 280), the odds ratios (OR) for moderate/severe depression (PHQ-9 ≥ 10) were higher for SMVs with one mild TBI (n = 358) OR: 1.62 (95% confidence interval [CI] 1.09-2.40, p = 0.016) and two or more mild TBIs (n = 818) OR: 1.84 (95% CI 1.31-2.59, p < 0.001). Risk differences across groups were assessed in stratified linear models, which found that depression symptoms were elevated in those with a history of multiple mild TBIs compared with those who had a single mild TBI (p < 0.001). Combat deployment-related injuries were also associated with higher depression scores than injuries occurring in non-combat or civilian settings (p < 0.001). Increased rates of depression after mild TBI persisted in the absence of post-traumatic stress disorder. Both men and women SMVs separately exhibited significantly increased depressive symptom scores if they had had combat-related mild TBI. These results suggest that contextual information, gender, and prior injury history may influence long-term mental health outcomes among SMVs with mild TBI exposure.

Longitudinal Biochemical and Behavioral Alterations in a Gyrencephalic Model of Blast-Related Mild Traumatic Brain Injury

Blast-related traumatic brain injury (bTBI) is a major cause of neurological disorders in the U.S. military that can adversely impact some civilian populations as well and can lead to lifelong deficits and diminished quality of life. Among these types of injuries, the long-term sequelae are poorly understood because of variability in intensity and number of the blast exposure, as well as the range of subsequent symptoms that can overlap with those resulting from other traumatic events (e.g., post-traumatic stress disorder). Despite the valuable insights that rodent models have provided, there is a growing interest in using injury models using species with neuroanatomical features that more closely resemble the human brain. With this purpose, we established a gyrencephalic model of blast injury in ferrets, which underwent blast exposure applying conditions that closely mimic those associated with primary blast injuries to warfighters. In this study, we evaluated brain biochemical, microstructural, and behavioral profiles after blast exposure using in vivo longitudinal magnetic resonance imaging, histology, and behavioral assessments. In ferrets subjected to blast, the following alterations were found: 1) heightened impulsivity in decision making associated with pre-frontal cortex/amygdalar axis dysfunction; 2) transiently increased glutamate levels that are consistent with earlier findings during subacute stages post-TBI and may be involved in concomitant behavioral deficits; 3) abnormally high brain N-acetylaspartate levels that potentially reveal disrupted lipid synthesis and/or energy metabolism; and 4) dysfunction of pre-frontal cortex/auditory cortex signaling cascades that may reflect similar perturbations underlying secondary psychiatric disorders observed in warfighters after blast exposure.

The game changer: UCH-L1 and GFAP-based blood test as the first marketed in vitro diagnostic test for mild traumatic brain injury

INTRODUCTION

Major organ-based in vitro diagnostic (IVD) tests like ALT/AST for the liver and cardiac troponins for the heart are established, but an approved IVD blood test for the brain has been missing, highlighting a gap in medical diagnostics.

AREAS COVERED

In response to this need, Abbott Diagnostics secured FDA clearance in 2021 for the i-STAT Alinity™, a point-of-care plasma blood test for mild traumatic brain injury (TBI). BioMerieux VIDAS, also approved in Europe, utilizes two brain-derived protein biomarkers: neuronal ubiquitin C-terminal hydrolase-L1 (UCH-L1) and glial fibrillary acidic protein (GFAP). These biomarkers, which are typically present in minimal amounts in healthy individuals, are instrumental in diagnosing mild TBI with potential brain lesions. The study explores how UCH-L1 and GFAP levels increase significantly in the bloodstream following traumatic brain injury, aiding in early and accurate diagnosis.

EXPERT OPINION

The introduction of the i-STAT Alinity™ and the Biomerieux VIDAS TBI blood tests mark a groundbreaking development in TBI diagnosis. It paves the way for the integration of TBI biomarker tools into clinical practice and therapeutic trials, enhancing the precision medicine approach by generating valuable data. This advancement is a critical step in addressing the long-standing gap in brain-related diagnostics and promises to revolutionize the management and treatment of mild TBI.

Subjective cognitive complaints and objective cognitive functioning in combat veterans: Effects of PTSD and deployment mild TBI

OBJECTIVES

(1) Examine the relationship between subjective cognitive complaints and objective cognitive functioning in combat veterans; and (2) evaluate conditional effects of posttraumatic stress disorder (PTSD) and deployment-related mild traumatic brain injury (TBI) within that relationship.

METHOD

Combat veterans (N = 225, 86.22% male) completed a lifetime TBI interview, a structured interview assessing PTSD symptoms, a neuropsychological assessment battery, and a self-report measure of cognitive symptoms.

RESULTS

All correlations between subjective cognitive complaints and objective cognitive measures were not statistically significant. Hierarchical linear regression indicated that cognitive performance was not significantly related to cognitive complaints, but both PTSD diagnosis and history of deployment mild TBI explained a significant amount of unique variance in self-reported cognitive symptoms. Interactions between the studied variables were not significant.

CONCLUSIONS

PTSD and history of deployment mild TBI were uniquely related to cognitive complaints, but cognitive test performance was not. No confounding effects of PTSD or deployment mild TBI were observed in the relationship between cognitive performance and cognitive complaints. This provides support that symptom distress may be a better explanatory factor for perception of lower cognitive functioning than actual cognitive performance.

Levels of Arachidonic Acid-Derived Oxylipins and Anandamide Are Elevated Among Military APOE ɛ4 Carriers With a History of Mild Traumatic Brain Injury and Post-Traumatic Stress Disorder Symptoms

Currently approved blood biomarkers detect intracranial lesions in adult patients with mild to moderate traumatic brain injury (TBI) acutely post-injury. However, blood biomarkers are still needed to help with a differential diagnosis of mild TBI (mTBI) and post-traumatic stress disorder (PTSD) at chronic post-injury time points. Owing to the association between phospholipid (PL) dysfunction and chronic consequences of TBI, we hypothesized that examining bioactive PL metabolites (oxylipins and ethanolamides) would help identify long-term lipid changes associated with mTBI and PTSD. Lipid extracts of plasma from active-duty soldiers deployed to the Iraq/Afghanistan wars (control = 52, mTBI = 21, PTSD = 34, and TBI + PTSD = 13) were subjected to liquid chromatography/mass spectrometry analysis to examine oxylipins and ethanolamides. Linear regression analyses followed by post hoc comparisons were performed to assess the association of these lipids with diagnostic classifications. Significant differences were found in oxylipins derived from arachidonic acid (AA) between controls and mTBI, PTSD, and mTBI + PTSD groups. Levels of AA-derived oxylipins through the cytochrome P450 pathways and anandamide were significantly elevated among mTBI + PTSD patients who were carriers of the apolipoprotein E E4 allele. These studies demonstrate that AA-derived oxylipins and anandamide may be unique blood biomarkers of PTSD and mTBI + PTSD. Further, these AA metabolites may be indicative of an underlying inflammatory process that warrants further investigation. Future validation studies in larger cohorts are required to determine a potential application of this approach in providing a differential diagnosis of mTBI and PTSD in a clinical setting.

The Toronto Concussion Study: a prospective investigation of characteristics in a cohort of adults from the general population seeking care following acute concussion, 2016-2020

Purpose

There is limited research regarding the characteristics of those from the general population who seek care following acute concussion.

Methods

To address this gap, a large cohort of 473 adults diagnosed with an acute concussion (female participants = 287; male participants = 186) was followed using objective measures prospectively over 16 weeks beginning at a mean of 5.1 days post-injury.

Results

Falls were the most common mechanism of injury (MOI) (n = 137, 29.0%), followed by sports-related recreation (n = 119, 25.2%). Male participants were more likely to be injured playing recreational sports or in a violence-related incident; female participants were more likely to be injured by falling. Post-traumatic amnesia (PTA) was reported by 80 participants (16.9 %), and loss of consciousness (LOC) was reported by 110 (23.3%). In total, 54 participants (11.4%) reported both PTA and LOC. Male participants had significantly higher rates of PTA and LOC after their injury compared to their female counterparts. Higher initial symptom burden was associated with a longer duration of recovery for both male and female participants. Female participants had more symptoms and higher severity of symptoms at presentation compared to male participants. Female participants were identified to have a longer recovery duration, with a mean survival time of 6.50 weeks compared to 5.45 weeks in male participants (p < 0.0001). A relatively high proportion of female and male participants in this study reported premorbid diagnoses of depression and anxiety compared to general population characteristics.

Conclusion

Although premorbid diagnoses of depression and/or anxiety were associated with higher symptom burden at the initial visit, the duration of symptoms was not directly associated with a pre-injury history of psychological/psychiatric disturbance. This cohort of adults, from the general population, seeking care for their acute concussion attained clinical and functional recovery over a period of 4-12 weeks.

Persistence of Hyper-Ramified Microglia in Porcine Cortical Gray Matter after Mild Traumatic Brain Injury

Traumatic brain injury (TBI) is a major contributor to morbidity and mortality in the United States as several million people visit the emergency department every year due to TBI exposures. Unfortunately, there is still no consensus on the pathology underlying mild TBI, the most common severity sub-type of TBI. Previous preclinical and post-mortem human studies have detailed the presence of diffuse axonal injury following TBI, suggesting that white matter pathology is the predominant pathology of diffuse brain injury. However, the inertial loading produced by TBI results in strain fields in both gray and white matter. In order to further characterize gray matter pathology in mild TBI, our lab used a pig model (n = 25) of closed-head rotational acceleration-induced TBI to evaluate blood-brain barrier disruptions, neurodegeneration, astrogliosis, and microglial reactivity in the cerebral cortex out to 1 year post-injury. Immunohistochemical staining revealed the presence of a hyper-ramified microglial phenotype-more branches, junctions, endpoints, and longer summed process length-at 30 days post injury (DPI) out to 1 year post injury in the cingulate gyrus (p < 0.05), and at acute and subacute timepoints in the inferior temporal gyrus (p < 0.05). Interestingly, we did not find neuronal loss or astroglial reactivity paired with these chronic microglia changes. However, we observed an increase in fibrinogen reactivity-a measure of blood-brain barrier disruption-predominately in the gray matter at 3 DPI (p = 0.0003) which resolved to sham levels by 7 DPI out to chronic timepoints. Future studies should employ gene expression assays, neuroimaging, and behavioral assays to elucidate the effects of these hyper-ramified microglia, particularly related to neuroplasticity and responses to potential subsequent insults. Further understanding of the brain's inflammatory activity after mild TBI will hopefully provide understanding of pathophysiology that translates to clinical treatment for TBI.

Mature and Myelinating Oligodendrocytes Are Specifically Vulnerable to Mild Fluid Percussion Injury in Mice

Myelin loss and oligodendrocyte death are well documented in patients with traumatic brain injury (TBI), as well as in experimental animal models after moderate-to-severe TBI. In comparison, mild TBI (mTBI) does not necessarily result in myelin loss or oligodendrocyte death, but causes structural alterations in the myelin. To gain more insight into the impact of mTBI on oligodendrocyte lineage in the adult brain, we subjected mice to mild lateral fluid percussion injury (mFPI) and characterized the early impact (1 and 3 days post-injury) on oligodendrocytes in the corpus callosum using multiple oligodendrocyte lineage markers (platelet-derived growth factor receptor [PDGFR]-α, glutathione S-transferase [GST]-π, CC1, breast carcinoma-amplified sequence 1 [BCAS1], myelin basic protein [MBP], myelin-associated glycoprotein [MAG], proteolipid protein [PLP], and FluoroMyelin™). Two regions of the corpus callosum in relation to the impact site were analyzed: areas near (focal) and anterior (distal) to the impact site. mFPI did not result in oligodendrocyte death in either the focal or distal corpus callosum, nor impact on oligodendrocyte precursors (PDGFR-α+) and GST-π+ oligodendrocyte numbers. In the focal but not distal corpus callosum, mFPI caused a decrease in CC1+ as well as BCAS1+ actively myelinating oligodendrocytes and reduced FluoroMyelin intensity without altering myelin protein expression (MBP, PLP, and MAG). Disruption in node-paranode organization and loss of Nav1.6+ nodes were observed in both the focal and distal regions, even in areas without obvious axonal damage. Altogether, our study shows regional differences in mature and myelinating oligodendrocyte in response to mFPI. Further, mFPI elicits a widespread impact on node-paranode organization that affects regions both close to and remotely located from the site of injury.

Behaviour outcomes three months after mild TBI in preschool children

This study examined parents' report of behaviour in preschoolers after a mild traumatic brain injury (mTBI), compared the proportion of preschoolers with elevated behaviour ratings between the mTBI and limb injury (LI) groups, and explored injury, premorbid child, and parent variables that may be associated with parents' report of behaviour at three months post-injury. Children aged 2-5 years with a mTBI (n = 13) or mild LI (n = 6) were recruited from the emergency department. Behaviour was assessed using the Child Behaviour Checklist. Preliminary findings showed that post-injury behaviour ratings remained in the normal range. The mTBI group had higher scores than the LI group at three months post-injury in terms of sleep; however, this may have been pre-existing. Two children with mTBI received borderline-clinically significant ratings on diagnostic-level anxiety problems at the three-month follow-up, while none of the limb-injured controls obtained elevated behaviour ratings. Parent-rated post-injury behaviour was significantly associated with premorbid child functioning and parental stress, which needs to be explored in greater detail using larger preschool mTBI samples.

Prevalence of comorbidities post mild traumatic brain injuries: a traumatic brain injury model systems study

Traumatic brain injury (TBI) is associated with an increased risk of long-lasting health-related complications. Survivors of brain trauma often experience comorbidities which could further dampen functional recovery and severely interfere with their day-to-day functioning after injury. Of the three TBI severity types, mild TBI constitutes a significant proportion of total TBI cases, yet a comprehensive study on medical and psychiatric complications experienced by mild TBI subjects at a particular time point is missing in the field. In this study, we aim to quantify the prevalence of psychiatric and medical comorbidities post mild TBI and understand how these comorbidities are influenced by demographic factors (age, and sex) through secondary analysis of patient data from the TBI Model Systems (TBIMS) national database. Utilizing self-reported information from National Health and Nutrition Examination Survey (NHANES), we have performed this analysis on subjects who received inpatient rehabilitation at 5 years post mild TBI. Our analysis revealed that psychiatric comorbidities (anxiety, depression, and post-traumatic stress disorder (PTSD)), chronic pain, and cardiovascular comorbidities were common among survivors with mild TBI. Furthermore, depression exhibits an increased prevalence in the younger compared to an older cohort of subjects whereas the prevalence of rheumatologic, ophthalmological, and cardiovascular comorbidities was higher in the older cohort. Lastly, female survivors of mild TBI demonstrated increased odds of developing PTSD compared to male subjects. The findings of this study would motivate additional analysis and research in the field and could have broader implications for the management of comorbidities after mild TBI.

Barriers and facilitators to the uptake of the Concussion Awareness Training Tool as continuing medical education in primary care

Aim

Continuing medical education (CME) informs physicians on current research. The Concussion Awareness Training Tool (CATT) provides education on concussion diagnosis and treatment. The aims of this study were to explore physician CME practices and preferences, understand barriers and facilitators to implementing the CATT as CME, and provide recommendations.

Materials & methods

Physicians in British Columbia, Canada participated in an online survey and telephone interview. Descriptive analysis of quantitative data, and text-based data analysis were undertaken to identify themes.

Results

Barriers included lack of time and awareness of the resource. Facilitators were its ease of use, accessibility, conciseness and comprehensiveness.

Conclusion

The perceptions of barriers and facilitators reported by physicians are important to understand and better promote the use of the CATT.

Beyond symptomatic diagnosis of mild traumatic brain injury

It is commonly assumed that there is no brain injury if there are no noticeable symptoms following a head impact. There is growing evidence that traumatic brain injuries can occur with no outward symptoms and that the damage from these injuries can accumulate over time resulting in disease and impairment later in life. It is time to rethink the role that symptoms play in traumatic brain injury and adopt a quantitative understanding of brain health at the cellular level to improve the way we diagnose, prevent, and ultimately heal brain injury.

Utility of Person-Environment-Occupation model in exploring sex-specific causes of work-related traumatic brain injury: a retrospective chart review

BACKGROUND

Work-related traumatic brain injury (wr-TBI) is on the rise. The pre-injury period, a significant consideration for preventive initiatives, is largely unexplored.

OBJECTIVES

To identify Person-Environment-Occupation (PEO) variables associated with wr-TBI to inform sex-specific primary prevention.

METHODS

Retrospective chart review data were analyses. Two-tailed t-test and chi-squared tests were used to study sex differences. Multivariate logistic regression models of wr-TBI were fit with a priori defined PEO variables.

RESULTS

The sample comprised 330 consecutive workers with wr-TBI (40.8 ± 11.1 years old, 71% male). Sex differences were observed across PEO variables. In multivariable logistic regression analyses the odds of sustaining a wr-TBI from a fall increased with the presence of a mood disorder and participation in non-labourer occupations (odds ratio (OR) 2.89 (95% CI 1.06-7.89) and OR 2.89 (95% CI 1.06-7.89), respectively) and decreased being a male (OR 0.31 (95% CI 0.17-0.54)). The odds of sustaining a wr-TBI from being striken by an object was greater in workers with prior head injury (OR 2.8 (95% CI 1.24-6.45)). None of the variables studied were associated with wr-TBI sustained from being striken against an object.

CONCLUSIONS

Workers' health status pre-injury is associated with external causes of wr-TBI. Sex differences across PEO categories warrant further study.

Computed Tomography Lesions and Their Association with Global Outcome in Young People with Mild Traumatic Brain Injury

Mild traumatic brain injury (mTBI) can be accompanied by structural damage to the brain. Here, we investigated how the presence of intracranial traumatic computed tomography (CT) pathologies relates to the global functional outcome in young patients one year after mTBI. All patients with mTBI (Glasgow Coma Scale: 13-15) ≤24 years in the multi-center, prospective, observational Collaborative European NeuroTrauma Effectiveness Research in TBI (CENTER-TBI) study were included. Patient demographics and CT findings were assessed at admission, and the Glasgow Outcome Scale Extended (GOSE) was evaluated at 12 months follow-up. The association between a "positive CT" (at least one of the following: epidural hematoma, subdural hematoma, traumatic subarachnoid hemorrhage (tSAH), intraventricular hemorrhage, subdural collection mixed density, contusion, traumatic axonal injury) and functional outcome (GOSE) was assessed using multi-variable mixed ordinal and logistic regression models. A total of 462 patients with mTBI and initial brain CT from 46 study centers were included. The median age was 19 (17-22) years, and 322 (70%) were males. CT imaging showed a traumatic intracranial pathology in 171 patients (37%), most commonly tSAH (48%), contusions (40%), and epidural hematomas (37%). Patients with a positive CT scan were less likely to achieve a complete recovery 12 months post-injury. The presence of any CT abnormality was associated with both lower GOSE scores (odds ratio [OR]: 0.39 [0.24-0.63]) and incomplete recovery (GOSE <8; OR: 0.41 [0.25-0.68]), also when adjusted for demographical and clinical baseline factors. The presence of intracranial traumatic CT pathologies was predictive of outcome 12 months after mTBI in young patients, which might help to identify candidates for early follow-up and additional care.

The Role of Reported Affective Symptoms and Anxiety in Recovery Trajectories After Sport-Related Concussion

BACKGROUND

There is growing awareness and clinical interest in athletes with affective symptoms after sport-related concussion (SRC), as these symptoms may contribute to overall symptoms and represent a modifiable risk factor of longer recovery. However, evidence of their effects on the entire return-to-play (RTP) trajectory, particularly among women and men, is limited.

PURPOSE/HYPOTHESIS

To examine the relationship between affective symptom reporting and RTP progression after SRC among a cohort of Division 1 student-athletes. We hypothesized that those endorsing affective symptoms, specifically nervous-anxious symptoms, spend more time in RTP progression and recovery.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

Using SRC data from the Ivy League-Big Ten Epidemiology of Concussion Study among varsity athletes through February 2020, we identified the 4 affective symptoms from the Sport Concussion Assessment Tool symptom inventory. We modeled the relationship between a 4-category affective symptom variable and time to symptom resolution, RTP, and RTP progression, adjusting for nonaffective symptom prevalence and concussion history. Cox regressions were used to estimate hazard ratios for time to event outcomes, and linear regressions were used to evaluate mean differences for continuous outcomes.

RESULTS

Among 2077 student-athletes (men, 63.5%) with SRC symptoms, affective symptom prevalence was 47.6% and 44.3% in women and men, respectively, and nervous-anxious prevalence was 24.2% and 22.5%, respectively. When comparing women with and without co-occurring affective symptoms, rates of symptom resolution and RTP were significantly lower in those with affective symptoms, and women with nervous-anxious symptoms spent significantly longer in RTP progression. When comparing men with and without co-occurring affective symptoms, rates of symptom resolution and RTP were significantly lower in those with co-occurring affective symptoms, and affective symptoms were not associated with time in RTP progression.

CONCLUSION

Student-athletes with affective symptoms and nervous-anxious symptoms exhibited delayed clinical recovery and RTP timelines, particularly for time in RTP. Symptom prevalence and concussion history contributed to this; however, unmeasured confounding remains, as indicated by the poor model fit. This study motivates future work to explore affective symptoms and RTP timelines, considering anxiety and risk/protective factors over time.

Classification Criteria and Rates of Persistent Postconcussive Symptoms in Children: A Systematic Review and Meta-Analysis

OBJECTIVE

To provide a systematic review of studies examining the proportion of children with persistent postconcussive symptoms (PPCS) and to examine potential moderators of prevalence.

STUDY DESIGN

Searches were conducted in MEDLINE, Embase, PsycINFO, Scopus, and Cochrane Central Register of Controlled Trials on April 16, 2020. Criteria for study inclusion were children aged <18 years with concussion or mild traumatic brain injury, operational definition of PPCS, assessment of postconcussive symptoms at least 4 weeks postinjury, sample sizes and proportion with PPCS available, and study published in English. Definition of PPCS, sample size, proportion of participants identified with PPCS, child sex and age at injury, time postinjury, premorbid symptoms, diagnosis (concussion or mild traumatic brain injury), and study publication year were extracted from each article. Study quality was assessed using the Newcastle-Ottawa Scale.

RESULTS

Thirteen studies, with a total of 5307 participants, were included in our analysis. The proportion of children identified with PPCS was 35.1% (weighted average; 95% CI, 26.3%-45.0%). The prevalence of PPCS was higher in older and female children who presented for care at concussion clinics, and in more recent publications.

CONCLUSIONS

Approximately one-third of children with concussion/mild traumatic brain injury will experience PPCS. Age, sex, and point of care could help identify children at high risk for PPCS.

Updated Review of the Evidence Supporting the Medical and Legal Use of NeuroQuant® and NeuroGage® in Patients With Traumatic Brain Injury

Over 40 years of research have shown that traumatic brain injury affects brain volume. However, technical and practical limitations made it difficult to detect brain volume abnormalities in patients suffering from chronic effects of mild or moderate traumatic brain injury. This situation improved in 2006 with the FDA clearance of NeuroQuant®, a commercially available, computer-automated software program for measuring MRI brain volume in human subjects. More recent strides were made with the introduction of NeuroGage®, commercially available software that is based on NeuroQuant® and extends its utility in several ways. Studies using these and similar methods have found that most patients with chronic mild or moderate traumatic brain injury have brain volume abnormalities, and several of these studies found-surprisingly-more abnormal enlargement than atrophy. More generally, 102 peer-reviewed studies have supported the reliability and validity of NeuroQuant® and NeuroGage®. Furthermore, this updated version of a previous review addresses whether NeuroQuant® and NeuroGage® meet the Daubert standard for admissibility in court. It concludes that NeuroQuant® and NeuroGage® meet the Daubert standard based on their reliability, validity, and objectivity. Due to the improvements in technology over the years, these brain volumetric techniques are practical and readily available for clinical or forensic use, and thus they are important tools for detecting signs of brain injury.

Epilepsy Due to Mild TBI in Children: An Experience at a Tertiary Referral Center

Rationale: Posttraumatic epilepsy (PTE) is a common cause of morbidity in children after a traumatic brain injury (TBI), occurring in 10–20% of children following severe TBI. PTE is diagnosed after two or more unprovoked seizures occurring 1-week post TBI. More often, studies have focused on children with epilepsy due to severe TBI. We aim to understand the utility of head computed tomography (HCT), EEG, and the risk of developing drug-resistant epilepsy in children after mild TBI. Method: We retrospectively studied 321 children with TBI at a tertiary pediatric referral center during a 10-year period. Mild TBI was defined as loss of consciousness (LOC) or amnesia < 30 min, moderate TBI as LOC or amnesia between 30 min and 1 day, and severe TBI as LOC or amnesia > 1 day, subdural hemorrhage, or contusion. Multiple clinical variables were reviewed, including past and present antiepileptic drug(s), seizure control, and mode of injury. First and subsequent post-TBI EEGs/prolonged video-EEGs were obtained acutely, subacutely, and/or chronically (range, day 1–3 years, median 1 month). Descriptive analyses were conducted using medians and ranges for continuous data. Categorical data were reported using frequencies and percentages, while comparisons between groups were made using Fisher’s exact test for small sample sizes. Results: Forty-seven children were diagnosed with posttraumatic epilepsy: eight children (17%) due to mild TBI, 39 children (83%) due to severe TBI. For the eight children with mild TBI whom all had an accidental trauma (non-inflicted), the median follow-up time was 25 months (range 1.5 months–84 months). The median age was 10 years (range 4–18 years), and the median age at the time of injury was seven years (range: 23 months–13 years). No relevant previous medical history was present for six patients (80%), and two patients’ (20%) relevant previous medical histories were unknown. Seven patients (88%) had no history of seizures, and patient #6 (12%) had unknown seizure history. Six patients (75%) had normal routine EEG(s). Patient #6 (13%) had an abnormal VEEG 3 months after the initial normal routine EEG, while patient #1 (13%) had an initial prolonged EEG 8 months after TBI. Compared to the 39 patients with severe TBI, 31 (79%) of whom had abnormal EEGs (routine and/or prolonged with video), mild TBI patients were more likely to have normal EEGs, p = 0.005. Head CT scans were obtained acutely for seven patients (90%), all of which were normal. One patient only had brain magnetic resonance imaging (MRI) 8 months after the injury. Compared to the 39 patients with severe TBI, all of whom had abnormal HCTs, mild TBI patients were less likely to have abnormal HCTs, p < 0.0001. In patients with mild TBI, no patient had both abnormal EEG/VEEG and HCT, and no one was on more than one Antiepileptic drug (AED), p < 0.005. Six patients (75%) had MRIs, of which five (63%) were normal. Two patients (#1, 7) did not have MRIs, while one patient’s (#4) MRI was unavailable. Five patients (63%) had a seizure <24 h post TBI, while the rest had seizures after the first week of injury. Conclusion: Children with epilepsy due to mild TBI, loss of consciousness, or amnesia < 30 min are more likely to have normal HCT and EEG and to be on 0–1 AED. Limitations of our study include the small sample size and retrospective design. The current findings add to the paucity of data in children who suffer from epilepsy due to mild TBI.

Characterizing Sleep and Wakefulness in the Acute Phase of Concussion in the General Population: A Naturalistic Cohort from the Toronto Concussion Study

Growing literature links concussion to changes in sleep and wakefulness in humans and in rodent models. Sleep has been linked with synaptic reorganization under other conditions; however, the characterization and role of sleep after acute concussion remains poorly understood. While much research has focused on insomnia among patients with chronic or persistent concussion symptoms, there is limited understanding of sleep and acute concussion, its potential role in recovery, and associated risk factors for the development of chronic sleep disturbance. Studies to date are limited by small sample sizes of primarily athlete or military populations. Additional studies among the general population are critical to inform best practice guidelines. We examined the sleep and daytime wakefulness of 472 adults from a naturalistic general population cohort (mean age, 33.3 years, females = 60.8%) within seven days of diagnosed concussion, using a validated, condition-specific measure, the Sleep and Concussion Questionnaire. Participants identified immediate changes in sleep characterized by hypersomnia and difficulty maintaining daytime wakefulness; 35% considered these changes as moderate to severe and 79% required monitoring or follow-up. Females experienced significantly greater severity of changes in sleep compared with males. Positive correlations between severity of sleep and pain and headache were identified. Differences by sex are an important consideration for early intervention and long-term monitoring. Because sleep was compromised by pain, pain management is also an integral part of early intervention. Our findings suggest that assessment of sleep beginning in the acute stage is a critical component of concussion management in the general population.

Relationships between injury kinematics, neurological recovery, and pathology following concussion

Mild traumatic brain injury affects millions of individuals annually primarily through falls, traffic collisions, or blunt trauma and can generate symptoms that persist for years. Closed-head rotational loading is the most common cause of mild traumatic brain injury and is defined by a rapid rotational acceleration of brain tissue within an intact skull. Injury kinematics-the mechanical descriptors of injury-inducing motion-explain movement of the head, which govern energy transfer, and, therefore, determine injury severity. However, the relationship between closed-head rotational injury kinematics-such as angular velocity, angular acceleration, and injury duration-and outcome after mild traumatic brain injury is not completely understood. To address this gap in knowledge, we analysed archived surgical records of 24 swine experiencing a diffuse closed-head rotational acceleration mild traumatic brain injury against 12 sham animals. Kinematics were contrasted against acute recovery outcomes, specifically apnea time, extubation time, standing time, and recovery duration. Compared to controls, animals experiencing a mild traumatic brain injury were far more likely to have apnea (P < 0.001), shorter time to extubation (P = 0.023), and longer time from extubation to standing (P = 0.006). Using least absolute shrinkage and selection operator-based regressions, kinematic parameters, including maximum negative angular velocity and time from peak angular velocity to maximum angular deceleration, were selected to explain variation in apnea time, standing time, and recovery duration. Simplified linear models employing the least absolute shrinkage and selection operator-selected variables explained a modest degree of variation in apnea time (adjusted R 2 = 0.18), standing time (adjusted R 2 = 0.19), and recovery duration (adjusted R 2 = 0.27). Neuropathology was correlated with multiple injury kinematics, with maximum angular acceleration exhibiting the strongest correlation (R 2 = 0.66). Together, these data suggest the interplay between multiple injury kinematics, including maximum negative angular velocity (immediately preceding cessation of head motion) and time from peak angular velocity to maximum angular deceleration, best explain acute recovery metrics and neuropathology after mild traumatic brain injury in swine. Future experiments that independently manipulate individual kinematic parameters could be instrumental in developing translational diagnostics for clinical mild traumatic brain injury.

Association between white matter organization and cognitive performance in athletes with a history of sport-related concussion

INTRODUCTION

Impairments in cognitive performance after sport-related concussion (SRC) typically resolve within weeks of the injury, whereas alterations to white matter (WM) organization have been found to persist longer into the chronic injury stage. However, longer-term associations between cognition and WM organization following SRC have not been studied. The objective of this study was to compare WM organization and cognitive performance in collegiate athletes an average of almost 4 years post-SRC to athletes with no history of SRC.

METHOD

National Collegiate Athletic Association Division III athletes (n = 71, age = 19.3 ± 1.2; 14 with self-reported SRC) completed a neurocognitive assessment and diffusion tensor imaging (DTI). WM organization was assessed by extracting measures of fractional anisotropy (FA), mean diffusivity (MD), and radial diffusivity (RD) from 20 WM regions of interest (ROIs). Multivariate partial least squares analyses were used to compare athletes with and without a history of SRC and assess relationships between DTI-derived metrics of WM organization and cognitive measures.

RESULTS

Cognitive performance and ROI metrics did not differ between athletes with and without prior SRC. However, among athletes with a history of SRC, better executive function, processing speed, and memory but worse choice reaction time were associated with higher FA and lower MD and RD in several WM tracts.

CONCLUSION

Athletes with a history of SRC demonstrated greater associations between cognitive performance and WM organization, but also variability in the domains showing associations. Taken together, the findings demonstrate the importance of examining brain-behavior relationships several years after SRC to better gauge how WM organization supports cognition.

Deterioration After Mild Traumatic Brain Injury: A Single-Center Experience With Cost Analysis

Background: Most traumatic brain injuries (TBIs) are mild (GCS score of 13–15). Patients with mild TBI (mTBI) are generally in good condition. In some cases, a neurological deterioration (manifested by a drop of ≥1 point in GCS score) can occur and neurosurgical intervention (NI) may be needed. Because of that, these patients are frequently admitted to a hospital for observation. The aim of our study was to determine the number of patients with mTBI that deteriorate or need NI. We also considered an economic aspect of hospital admissions of these patients.

Methods: The study group consisted of 186 adult patients admitted to the neurosurgical department due to mTBI. Patients were divided into three groups according to an initial GCS score. The occurrence of deterioration, need for NI, length of stay (LOS), cost of stay and occurrence of death were analyzed.

Results: The deterioration was observed in 7 (3.76%) out of all cases. In 3 (1.61%) of them, the NI was needed. The average LOS was 7.96 days and it was closely linked with an initial GCS score (p < 0.001). The total cost of stay of all patients included in this study was about 1,188,668 PLN (306,357 USD).

Conclusion: The deterioration occurred in a small number of patients with mTBI, the need for NI was even less common. Hospitalization of these patients is expensive. Further studies with prognostic model helping decide on admission/discharge are necessary.

Invariance of the Bifactor Structure of Mild Traumatic Brain Injury (mTBI) Symptoms on the Rivermead Postconcussion Symptoms Questionnaire Across Time, Demographic Characteristics, and Clinical Groups: A TRACK-TBI Study

This study aimed to elucidate the structure of the Rivermead Postconcussion Symptoms Questionnaire (RPQ) and evaluate its longitudinal and group variance. Factor structures were developed and compared in 1,011 patients with mild traumatic brain injury (mTBI; i.e., Glasgow Coma Scale score 13-15) from the Transforming Research and Clinical Knowledge in TBI study, using RPQ data collected at 2 weeks, and 3, 6, and 12 months postinjury. A bifactor model specifying a general factor and emotional, cognitive, and visual symptom factors best represented the latent structure of the RPQ. The model evinced strict measurement invariance over time and across sex, age, race, psychiatric history, and mTBI severity groups, indicating that differences in symptom endorsement were completely accounted for by these latent dimensions. While highly unidimensional, the RPQ has multidimensional features observable through a bifactor model, which may help differentiate symptom expression patterns in the future.

Neuroradiologic Evaluation of MRI in High-Contact Sports

Background and Purpose: Athletes participating in high-contact sports experience repeated head trauma. Anatomical findings, such as a cavum septum pellucidum, prominent CSF spaces, and hippocampal volume reductions, have been observed in cases of mild traumatic brain injury. The extent to which these neuroanatomical findings are associated with high-contact sports is unknown. The purpose of this study was to determine whether there are subtle neuroanatomic differences between athletes participating in high-contact sports compared to low-contact athletic controls.

Materials and Methods: We performed longitudinal structural brain MRI scans in 63 football (high-contact) and 34 volleyball (low-contact control) male collegiate athletes with up to 4 years of follow-up, evaluating a total of 315 MRI scans. Board-certified neuroradiologists performed semi-quantitative visual analysis of neuroanatomic findings, including: cavum septum pellucidum type and size, extent of perivascular spaces, prominence of CSF spaces, white matter hyperintensities, arterial spin labeling perfusion asymmetries, fractional anisotropy holes, and hippocampal size.

Results: At baseline, cavum septum pellucidum length was greater in football compared to volleyball controls (p = 0.02). All other comparisons were statistically equivalent after multiple comparison correction. Within football at baseline, the following trends that did not survive multiple comparison correction were observed: more years of prior football exposure exhibited a trend toward more perivascular spaces (p = 0.03 uncorrected), and lower baseline Standardized Concussion Assessment Tool scores toward more perivascular spaces (p = 0.02 uncorrected) and a smaller right hippocampal size (p = 0.02 uncorrected).

Conclusion: Head impacts in high-contact sport (football) athletes may be associated with increased cavum septum pellucidum length compared to low-contact sport (volleyball) athletic controls. Other investigated neuroradiology metrics were generally equivalent between sports.

Blood-Brain Barrier Breakdown and Astrocyte Reactivity Evident in the Absence of Behavioral Changes after Repeated Traumatic Brain Injury

Repeated traumatic brain injuries (TBIs) cause debilitating effects. Without understanding the acute effects of repeated TBIs, treatment options to halt further degeneration and damage cannot be developed. This study sought to examine the acute effects of blood-brain barrier (BBB) dysfunction, edema, inflammation and behavioral changes after either a single or double TBI using a C57BL/6 mouse model. We examined the effects of one or two TBIs, of either a mild or moderate severity. Double injuries were spaced 7 days apart, and all analysis was performed 24 h post-injury. To examine edema and inflammation, protein levels of glial fibrillary acidic protein (GFAP), S100 calcium-binding protein B, interleukin-6, and matrix metallopeptidase 9 (MMP9) were analyzed. Aquaporin-4 (AQP4) and zonula occludens-1 (ZO-1) were analyzed to observe BBB dysfunction. Ionized calcium-binding adapter molecule 1 (IBA1) was analyzed to observe microglial activation. Rotarod, beam walking, and grip strength tests were used to measure changes in physical behavior post-injury. A sample size of ≥5 was used for all analysis. Double injuries led to an increase in BBB breakdown, as indicated by altered MMP-9, AQP4, and ZO-1 protein expression. Single injuries showed an increase in microglial activation, astrocyte activation, and BBB breakdown. Behavioral tasks showed no significant differences between injured and control groups. Based on our findings, we suggest that behavioral studies should not be used as the sole clinical indicator on brain tissue recovery. Analysis of markers such as IBA1, GFAP, MMP-9, AQP4, and ZO-1 provide valuable insight on pathophysiological response to injury.

The Savage Organizational Scoring System for the Rey-Osterrieth Complex Figure Test: Norms and New Data From Veterans in a Traumatic Brain Injury Clinic

The Rey-Osterrieth Complex Figure Test (RCFT) permits quantifying diverse cognitive abilities, including executive function (EF). We evaluated the psychometric properties of a scoring procedure for the RCFT, the Savage Organizational Scoring System (SOSS), that awards points for drawing the largest structural elements of the figures as continuous wholes. This was a two-phase study: first, we conducted a systematic literature search for studies using the SOSS, and aggregated previously published data for healthy controls to create a normative database; second, we observed performances from veterans evaluated for traumatic brain injury (TBI), examining the reliability of their SOSS scores, the SOSS correlations with two EF measures and the participants' self-reported cognitive functioning, and then compared their mean scores to normative expectations. Across our literature-derived normative database, the aggregated mean SOSS score was 4.12 (SD = 1.72), which was marginally higher than that of our veteran participants evaluated for TBI, 3.72 (SD = 1.79). The SOSS had modest internal consistency (α = .59). Unlike the criterion EF measures, the SOSS was not significantly related to self-reported cognitive functioning. The SOSS shared a small, significant correlation with Trails B and Shipley Abstraction; but RCFT Copy scores were more strongly related to these tests, and the SOSS added no significant incremental predictive value beyond the RCFT Copy score. However, SOSS scores did predict RCFT Recall beyond RCFT Copy scores. We conclude that the SOSS has modest reliability and is predictive of RCFT Recall scores, but it is not strongly correlated with other EF measures, and it is only minimally affected by mild TBI.

Mental Fatigue after Mild Traumatic Brain Injury in Relation to Cognitive Tests and Brain Imaging Methods

Most people recover within months after a mild traumatic brain injury (TBI) or concussion, but some will suffer from long-term fatigue with a reduced quality of life and the inability to maintain their employment status or education. For many people, mental fatigue is one of the most distressing and long-lasting symptoms following an mTBI. No efficient treatment options can be offered. The best method for measuring fatigue today is with fatigue self-assessment scales, there being no objective clinical tests available for mental fatigue. The aim here is to provide a narrative review and identify fatigue in relation to cognitive tests and brain imaging methods. Suggestions for future research are presented.

Insular Connectivity Is Associated With Self-Appraisal of Cognitive Function After a Concussion

Concussion is associated with acute cognitive impairments, with declines in processing speed and reaction time being common. In the clinical setting, these issues are identified via symptom assessments and neurocognitive test (NCT) batteries. Practice guidelines recommend integrating both symptoms and NCTs into clinical decision-making, but correlations between these measures are often poor. This suggests that many patients experience difficulties in the self-appraisal of cognitive issues. It is presently unclear what neural mechanisms give rise to appraisal mismatch after a concussion. One promising target is the insula, which regulates aspects of cognition, particularly interoception and self-monitoring. The present study tested the hypothesis that appraisal mismatch is due to altered functional connectivity of the insula to frontal and midline structures, with hypo-connectivity leading to under-reporting of cognitive issues and hyper-connectivity leading to over-reporting. Data were collected from 59 acutely concussed individuals and 136 normative controls, including symptom assessments, NCTs and magnetic resonance imaging (MRI) data. Analysis of resting-state functional MRI supported the hypothesis, identifying insular networks that were associated with appraisal mismatch in concussed athletes that included frontal, sensorimotor, and cingulate connections. Subsequent analysis of diffusion tensor imaging also determined that symptom over-reporting was associated with reduced fractional anisotropy and increased mean diffusivity of posterior white matter. These findings provide new insights into the mechanisms of cognitive appraisal mismatch after a concussion. They are of particular interest given the central role of symptom assessments in the diagnosis and clinical management of concussion.

Pediatric mild head trauma: is outpatient follow-up imaging necessary or beneficial?

OBJECTIVE

Pediatric traumatic brain injury (TBI) is the leading cause of death among children and is a significant cause of morbidity. However, the majority of injuries are mild (Glasgow Coma Scale score 13-15) without any need for neurosurgical intervention, and clinically significant neurological decline rarely occurs. Although the question of repeat imaging within the first 24 hours has been discussed in the past, the yield of short-term follow-up imaging has never been thoroughly described. In this paper, the authors focus on the yield of routine repeat imaging for pediatric mild TBI (mTBI) at the first clinic visit following hospital discharge.

METHODS

The authors conducted a retrospective review of patients with pediatric brain trauma who had been admitted to Johns Hopkins All Children's Hospital (JHACH). Patients with mTBI were identified, and their presentation, hospital course, and imaging results were reviewed. Those pediatric patients with mTBI who had undergone no procedure during their initial admission (only conservative treatment) were eligible for inclusion in the study. Two distinct groups were identified: patients who underwent repeated imaging at their follow-up clinic visit and those who underwent only clinical evaluation. Each case was assessed on whether the follow-up imaging had changed the follow-up course.

RESULTS

Between 2010 and 2015, 725 patients with TBI were admitted to JHACH. Of those, 548 patients qualified for analysis (i.e., those with mTBI who received conservative treatment without any procedure and were seen in the clinic for follow-up evaluation within 8 weeks after the trauma). A total of 392 patients had only clinic follow-up, without any diagnostic imaging study conducted as part of their clinic visit, whereas the other 156 patients underwent repeat MRI. Only 1 patient had a symptomatic change and was admitted after undergoing imaging. For 30 patients (19.2%), it was decided after imaging to continue the neurosurgical follow-up, which is a change from the institutional paradigm after mTBI. None of these patients had a change in neurological status, and all had a good functional status. All of these patients had one more follow-up in the clinic with new MRI, and none of them required further follow-up.

CONCLUSIONS

Children with mTBI are commonly followed up in the ambulatory clinic setting. The authors believe that for children with mTBI, normal clinical examination, and no new symptoms, there is no need for routine ambulatory imaging since the clinical yield of such is relatively low.

Single-Item Versus Multiple-Item Headache Ratings in Service Members Seeking Treatment for Brain Injury

INTRODUCTION

Headaches are the most common complaint after traumatic brain injury (TBI) and a significant cause of morbidity and disability among military personnel. Currently, there are a several measures which can assess headache disability, but there is a significant burden to assess each individual symptom given this heterogeneous polymorbid population. The objective of this proposed study was to validate the single headache item from the Neurobehavioral Symptom Inventory (NSI) compared to the 6-item Headache Impact Test (HIT-6).

MATERIALS AND METHODS

Participants included consecutive treatment-seeking outpatients at the Brain Injury Rehabilitation Service at the Brooke Army Medical Center from August 2007 to January 2010 who were administered a battery of assessment measures at initial intake, as part of usual care. Archival record review was conducted using procedures approved by the local Institutional Review Board. Inclusionary criteria included completion of both the HIT-6 and NSI. Participants with a cut-off score of >22 on the NSI Validity-10 were excluded in a post hoc analysis to validate findings among those who passed validity screen.

RESULTS

The Pearson correlation between the single-item NSI headache measure and the HIT-6 revealed at least 64% shared variance in this military sample (r = 0.8, p < 0.001), indication a high association between the two measures.

CONCLUSION

The NSI single-item headache measure adequately captured headache severity in this military cohort. Use of the single-item NSI headache measure may minimize survey burden on participants whose primary complaint is not headaches, or who present with multiple symptoms. Future studies are needed to validate the single-item headache measure in other samples.

A Role for the Amygdala in Impairments of Affective Behaviors Following Mild Traumatic Brain Injury

Mild traumatic brain injury (TBI) results in chronic affective disorders such as depression, anxiety, and fear that persist up to years following injury and significantly impair the quality of life for patients. Although a great deal of research has contributed to defining symptoms of mild TBI, there are no adequate drug therapies for brain-injured individuals. Preclinical studies have modeled these deficits in affective behaviors post-injury to understand the underlying mechanisms with a view to developing appropriate treatment strategies. These studies have also unveiled sex differences that contribute to the varying phenotypes associated with each behavior. Although clinical and preclinical studies have viewed these behavioral deficits as separate entities with unique neurobiological mechanisms, mechanistic similarities suggest that a novel approach is needed to advance research on drug therapy. This review will discuss the circuitry involved in the expression of deficits in affective behaviors following mild TBI in humans and animals and provide evidence that the manifestation of impairment in these behaviors stems from an amygdala-dependent emotional processing deficit. It will highlight mechanistic similarities between these different types of affective behaviors that can potentially advance mild TBI drug therapy by investigating treatments for the deficits in affective behaviors as one entity, requiring the same treatment.

Differential Leukocyte and Platelet Profiles in Distinct Models of Traumatic Brain Injury

Traumatic brain injury (TBI) affects over 3 million individuals every year in the U.S. There is growing appreciation that TBI can produce systemic modifications, which are in part propagated through blood–brain barrier (BBB) dysfunction and blood–brain cell interactions. As such, platelets and leukocytes contribute to mechanisms of thromboinflammation after TBI. While these mechanisms have been investigated in experimental models of contusion brain injury, less is known regarding acute alterations following mild closed head injury. To investigate the role of platelet dynamics and bioenergetics after TBI, we employed two distinct, well-established models of TBI in mice: the controlled cortical impact (CCI) model of contusion brain injury and the closed head injury (CHI) model of mild diffuse brain injury. Hematology parameters, platelet-neutrophil aggregation, and platelet respirometry were assessed acutely after injury. CCI resulted in an early drop in blood leukocyte counts, while CHI increased blood leukocyte counts early after injury. Platelet-neutrophil aggregation was altered acutely after CCI compared to sham. Furthermore, platelet bioenergetic coupling efficiency was transiently reduced at 6 h and increased at 24 h post-CCI. After CHI, oxidative phosphorylation in intact platelets was reduced at 6 h and increased at 24 h compared to sham. Taken together, these data demonstrate that brain trauma initiates alterations in platelet-leukocyte dynamics and platelet metabolism, which may be time- and injury-dependent, providing evidence that platelets carry a peripheral signature of brain injury. The unique trend of platelet bioenergetics after two distinct types of TBI suggests the potential for utilization in prognosis.

The Immune System's Role in the Consequences of Mild Traumatic Brain Injury (Concussion)

Mild traumatic brain injury (mild TBI), often referred to as concussion, is the most common form of TBI and affects millions of people each year. A history of mild TBI increases the risk of developing emotional and neurocognitive disorders later in life that can impact on day to day living. These include anxiety and depression, as well as neurodegenerative conditions such as chronic traumatic encephalopathy (CTE) and Alzheimer's disease (AD). Actions of brain resident or peripherally recruited immune cells are proposed to be key regulators across these diseases and mood disorders. Here, we will assess the impact of mild TBI on brain and patient health, and evaluate the recent evidence for immune cell involvement in its pathogenesis.

Plasma miR-9-3p and miR-136-3p as Potential Novel Diagnostic Biomarkers for Experimental and Human Mild Traumatic Brain Injury

Noninvasive, affordable circulating biomarkers for difficult-to-diagnose mild traumatic brain injury (mTBI) are an unmet medical need. Although blood microRNA (miRNA) levels are reportedly altered after traumatic brain injury (TBI), their diagnostic potential for mTBI remains inconclusive. We hypothesized that acutely altered plasma miRNAs could serve as diagnostic biomarkers both in the lateral fluid percussion injury (FPI) model and clinical mTBI. We performed plasma small RNA-sequencing from adult male Sprague-Dawley rats (n = 31) at 2 days post-TBI, followed by polymerase chain reaction (PCR)-based validation of selected candidates. miR-9a-3p, miR-136-3p, and miR-434-3p were identified as the most promising candidates at 2 days after lateral FPI. Digital droplet PCR (ddPCR) revealed 4.2-, 2.8-, and 4.6-fold elevations in miR-9a-3p, miR-136-3p, and miR-434-3p levels (p < 0.01 for all), respectively, distinguishing rats with mTBI from naïve rats with 100% sensitivity and specificity. DdPCR further identified a subpopulation of mTBI patients with plasma miR-9-3p (n = 7/15) and miR-136-3p (n = 5/15) levels higher than one standard deviation above the control mean at <2 days postinjury. In sTBI patients, plasma miR-9-3p levels were 6.5- and 9.2-fold in comparison to the mTBI and control groups, respectively. Thus, plasma miR-9-3p and miR-136-3p were identified as promising biomarker candidates for mTBI requiring further evaluation in a larger patient population.

Repetitive mTBI is associated with age-related reductions in cerebral blood flow but not cortical thickness

Mild traumatic brain injury (mTBI) is a risk factor for Alzheimer's disease (AD), and evidence suggests cerebrovascular dysregulation initiates deleterious neurodegenerative cascades. We examined whether mTBI history alters cerebral blood flow (CBF) and cortical thickness in regions vulnerable to early AD-related changes. Seventy-four young to middle-aged Veterans (mean age = 34, range = 23-48) underwent brain scans. Participants were divided into: (1) Veteran Controls (n = 27), (2) 1-2 mTBIs (n = 26), and (2) 3+ mTBIs (n = 21) groups. Resting CBF was measured using MP-PCASL. T1 structural scans were processed with FreeSurfer. CBF and cortical thickness estimates were extracted from nine AD-vulnerable regions. Regression analyses examined whether mTBI moderated the association between age, CBF, and cortical thickness. Regressions adjusting for sex and posttraumatic stress revealed mTBI moderated the association between age and CBF of the precuneus as well as superior and inferior parietal cortices (p's < .05); increasing age was associated with lower CBF in the 3+ mTBIs group, but not in the VCs or 1-2 mTBIs groups. mTBI did not moderate associations between age and cortical thickness (p's >.05). Repetitive mTBI is associated with cerebrovascular dysfunction in AD-vulnerable regions and may accelerate pathological aging trajectories.

Relationships between injury kinematics, neurological recovery, and pathology following concussion

Mild traumatic brain injury affects millions of individuals annually primarily through falls, traffic collisions, or blunt trauma and can generate symptoms that persist for years. Closed-head rotational loading is the most common cause of mild traumatic brain injury and is defined by a rapid rotational acceleration of brain tissue within an intact skull. Injury kinematics-the mechanical descriptors of injury-inducing motion-explain movement of the head, which govern energy transfer, and, therefore, determine injury severity. However, the relationship between closed-head rotational injury kinematics-such as angular velocity, angular acceleration, and injury duration-and outcome after mild traumatic brain injury is not completely understood. To address this gap in knowledge, we analysed archived surgical records of 24 swine experiencing a diffuse closed-head rotational acceleration mild traumatic brain injury against 12 sham animals. Kinematics were contrasted against acute recovery outcomes, specifically apnea time, extubation time, standing time, and recovery duration. Compared to controls, animals experiencing a mild traumatic brain injury were far more likely to have apnea (P < 0.001), shorter time to extubation (P = 0.023), and longer time from extubation to standing (P = 0.006). Using least absolute shrinkage and selection operator-based regressions, kinematic parameters, including maximum negative angular velocity and time from peak angular velocity to maximum angular deceleration, were selected to explain variation in apnea time, standing time, and recovery duration. Simplified linear models employing the least absolute shrinkage and selection operator-selected variables explained a modest degree of variation in apnea time (adjusted R ² = 0.18), standing time (adjusted R ² = 0.19), and recovery duration (adjusted R ² = 0.27). Neuropathology was correlated with multiple injury kinematics, with maximum angular acceleration exhibiting the strongest correlation (R ² = 0.66). Together, these data suggest the interplay between multiple injury kinematics, including maximum negative angular velocity (immediately preceding cessation of head motion) and time from peak angular velocity to maximum angular deceleration, best explain acute recovery metrics and neuropathology after mild traumatic brain injury in swine. Future experiments that independently manipulate individual kinematic parameters could be instrumental in developing translational diagnostics for clinical mild traumatic brain injury.

Predicting military readiness using objective and subjective indices of neuropsychological impairment in service members with mild traumatic brain injury

The military is interested in identifying factors to improve the readiness of service members with traumatic brain injury (TBI). TBI outcome studies have primarily used objective neuropsychological data interpreted using the absolute level of functioning (i.e., high average, average, low average), though research suggests it is also important to consider other objective indices of the relative degree of decline (e.g., mild, moderate, severe) and subjective complaints. The current study determined the predictive ability of objective indices of neuropsychological functioning (i.e., absolute level and the relative degree of decline) and subjective complaints (i.e., Neurobehavioral Symptom Inventory) in terms of military work status (i.e., return to duty, medically disabled, retired) for 113 service members with mild TBI. ANOVAs and post-hoc tests indicated individuals who were able to return to duty had higher absolute indices and lower relative decline scores in working memory and overall intelligence, as well as lower subjective neuropsychological complaints when compared to those who were disabled or retired. Multinomial logistic regression models generally supported these findings, except relative decline scores were not predictive of military work status likely due to issues of collinearity (i.e., relative decline scores are calculated using absolute scores). In conclusion, indices of absolute functioning and subjective neuropsychological impairments appear to be predictors of the ability to return to duty post-TBI in military populations, emphasizing the need to focus on cognitive reserve and emotional resilience as potential interventions.

Cognitive Training for Mild Traumatic Brain Injury and Posttraumatic Stress Disorder

Although there is evidence of mild cognitive impairments for many individuals with mild traumatic brain injury (mTBI) and posttraumatic stress disorder (PTSD), little research evaluating the effectiveness of cognitive training interventions has been conducted. This randomized controlled trial examined the effectiveness of a 9-h group cognitive training targeting higher-order functions, Strategic Memory Advanced Reasoning Training (SMART), compared to a 9-h psychoeducational control group in improving neurocognitive functioning in adults with mTBI and PTSD. A sample of 124 adults with histories of mild TBI (n = 117) and/or current diagnoses of PTSD (n = 84) were randomized into SMART (n = 66) or Brain Health Workshop (BHW; n = 58) and assessed at three time points: baseline, following training, and 6 months later. Participants completed a battery of neurocognitive tests, including a test of gist reasoning (a function directly targeted by SMART) as well as tests of verbal, visual, and working memory and executive functioning, functions commonly found to be mildly impaired in mTBI and PTSD. The two groups were compared on trajectories of change over time using linear mixed-effects models with restricted maximum likelihood (LMM). Contrary to our hypothesis that SMART would result in superior improvements compared to BHW, both groups displayed statistically and clinically significant improvements on measures of memory, executive functioning, and gist reasoning. Over 60% of the sample showed clinically significant improvements, indicating that gains can be found through psychoeducation alone. A longer SMART protocol may be warranted for clinical samples in order to observe gains over the comparison group.

The role of AT-SLP collaborations in return to academics following mTBI: A scoping review

Return-to-academics (RTA) for student-athletes with mild traumatic brain injury (mTBI) is crucial, but relatively understudied compared to return-to-play (RTP). The transient and unpredictable nature of symptoms surrounding mTBI often results in underreporting of neurocognitive symptoms, leading to a greater susceptibility for repeated TBIs, as well as posing impediments to the process of RTA. Athletic Trainers (ATs) and Speech-Language Pathologists (SLPs) are in a unique position to help student-athletes achieve a safe, timely, and effective RTA following mTBI. They typically work in middle/high schools and collegiate-level academic settings and often serve as members of concussion management teams. Compared to other allied health professions, ATs and SLPs are relatively new professions with evolving scopes of practice. Despite established guidelines and recommendations for their scope of practice in treating student-athletes with mTBI, there is a lacuna in research regarding their individual and collaborative roles in achieving RTA. The current scoping review was conducted with the main goal of exploring published literature pertaining to the roles of ATs and SLPs in achieving RTA for student-athletes with mTBI. Current implications, recommendations for integrating pre-service interprofessional education (IPE) experiences, and future directions for AT-SLP collaborations are discussed.

Serum Protein Biomarker Findings Reflective of Oxidative Stress and Vascular Abnormalities in Male, but Not Female, Collision Sport Athletes

Studies have indicated that concussive and sub-concussive brain injuries that are frequent during collision sports may lead to long-term neurological abnormalities, however there is a knowledge gap on how biological sex modifies outcomes. Blood-based biomarkers can help to identify the molecular pathology induced by brain injuries and to better understand how biological sex affects the molecular changes. We therefore analyzed serum protein biomarkers in male (n = 50) and female (n = 33) amateur Australian rules footballers (i.e., Australia's most participated collision sport), both with a history of concussion (HoC) and without a history of concussion (NoHoC). These profiles were compared to those of age-matched control male (n = 24) and female (n = 20) athletes with no history of neurotrauma or participation in collision sports. Serum levels of protein markers indicative of neuronal, axonal and glial injury (UCH-L1, NfL, tau, p-tau, GFAP, BLBP, PEA15), metabolic (4-HNE) and vascular changes (VEGF-A, vWF, CLDN5), and inflammation (HMGB1) were assessed using reverse phase protein microarrays. Male, but not female, footballers had increased serum levels of VEGF-A compared to controls regardless of concussion history. In addition, only male footballers who had HoC had increased serum levels of 4-HNE. These findings being restricted to males may be related to shorter collision sport career lengths for females compared to males. In summary, these findings show that male Australian rules footballers have elevated levels of serum biomarkers indicative of vascular abnormalities (VEGF-A) and oxidative stress (4-HNE) in comparison to non-collision control athletes. While future studies are required to determine how these findings relate to neurological function, serum levels of VEGF-A and 4-HNE may be useful to monitor subclinical neurological injury in males participating in collision sports.

Early versus Late Profiles of Inflammatory Cytokines after Mild Traumatic Brain Injury and Their Association with Neuropsychological Outcomes

Despite pre-clinical evidence for the role of inflammation in traumatic brain injury (TBI), there is limited data on inflammatory biomarkers in mild TBI (mTBI). In this study, we describe the profile of plasma inflammatory cytokines and explore associations between these cytokines and neuropsychological outcomes after mTBI. Patients with mTBI with negative computed tomography and orthopedic injury (OI) controls without mTBI were prospectively recruited from emergency rooms at three trauma centers. Plasma inflammatory cytokine levels were measured from venous whole-blood samples that were collected at enrollment (within 24 h of injury) and at 6 months after injury. Neuropsychological tests were performed at 1 week, 1 month, 3 months, and 6 months after the injury. Multivariate regression analysis was performed to identify associations between inflammatory cytokines and neuropsychological outcomes. A total of 53 mTBI and 24 OI controls were included in this study. The majority of patients were male (62.3%), and injured in motor vehicle accidents (37.7%). Plasma interleukin (IL)-2 (p = 0.01) and IL-6 (p = 0.01) within 24 h post-injury were significantly higher for mTBI patients compared with OI controls. Elevated plasma IL-2 at 24 h was associated with more severe 1-week post-concussive symptoms (p = 0.001). At 6 months, elevated plasma IL-10 was associated with greater depression scores (p = 0.004) and more severe post-traumatic stress disorder (PTSD) symptoms (p = 0.001). Plasma cytokine levels (within 24 h and at 6 months post-injury) were significantly associated with early and late post-concussive symptoms, PTSD, and depression scores after mTBI. These results highlight the potential role of inflammation in the pathophysiology of post-traumatic symptoms after mTBI.

Outcome measures from experimental traumatic brain injury in male rats vary with the complete temporal biomechanical profile of the injury event

Millions suffer a traumatic brain injury (TBI) each year wherein the outcomes associated with injury can vary greatly between individuals. This study postulates that variations in each biomechanical parameter of a head trauma lead to differences in histological and behavioral outcome measures that should be considered collectively in assessing injury. While trauma severity typically scales with the magnitude of injury, much less is known about the effects of rate and duration of the mechanical insult. In this study, a newly developed voice-coil fluid percussion injury system was used to investigate the effects of injury rate and fluid percussion impulse on a collection of post-injury outcomes in male rats. Collectively the data suggest a potential shift in the specificity and progression of neuronal injury and function rather than a general scaling of injury severity. While a faster, shorter fluid percussion first presents as a mild TBI, neuronal loss and some behavioral tasks were similar among the slower and faster fluid percussion injuries. This study concludes that the sequelae of neuronal degeneration and behavioral outcomes are related to the complete temporal profile of the fluid percussion and do not scale only with peak pressure.

Emergency department observation of mild traumatic brain injury with minor radiographic findings: shorter stays, less expensive, and no increased risk compared to hospital admission

OBJECTIVE

The management of mild traumatic brain injury (mTBI) with minor radiographic findings traditionally involves hospital admission for monitoring, although this practice is expensive with unclear benefit. We implemented a protocol to manage these patients in our emergency department observation unit (EDOU), hypothesizing that this pathway was cost effective and not associated with any difference in clinical outcome.

METHODS

mTBI patients with minor radiographic findings were managed under the EDOU protocol over a 3-year period from May 1, 2015 to April 30, 2018 (inclusions: ≥19 years old, isolated acute head trauma, normal neurological exam [except transient alteration in consciousness], and a computed tomography [CT] scan of the head with at least 1 of the following: cerebral contusions <1 cm in maximum extent, convexity subarachnoid hemorrhage, or closed, non-displaced skull fractures). These patients were retrospectively analyzed; clinical outcomes and charges were compared to a control cohort of matched mTBI hospital admissions over the preceding 3 years.

RESULTS

Sixty patients were observed in the EDOU over the 3-year period, and 85 patients were identified for the control cohort. There were no differences in rate of radiographic progression, neurological exam change, or surgical intervention, and the overall incidence of hemorrhagic expansion was low in both groups. The EDOU group had a significantly faster time to interval CT scan (Mean Difference (MD) 3.92 hours, [95%CI 1.65, 6.19]), P = 0.001), shorter length of stay (MD 0.59 days [95% CI 0.29, 0.89], P = 0.001), and lower encounter charges (MD $3428.51 [95%CI 925.60, 5931.42], P = 0.008). There were no differences in 30-day re-admission, 30-day mortality, or delayed chronic subdural formation, although there was a high rate of loss to follow-up in both groups.

CONCLUSIONS

Compared to hospital admission, observing mTBI patients with minor radiographic findings in the EDOU was associated with significantly shorter time to interval scanning, shorter length of stay, and lower encounter charges, but no difference in observed clinical outcome. The overall risk of hemorrhagic progression in this subset of mTBI was very low. Using this approach can reduce unnecessary admissions while potentially yielding patient care and economic benefits. When designing a protocol, close attention should be given to clear inclusion criteria and a formal mechanism for patient follow-up.

Introduction to a special issue on military neuropsychology: Serving those who serve

OBJECTIVE

The military has a long history with neuropsychology and its precursors. From developing intelligence tests during World War I, to developing early capacity and personality assessments during World War II, to forward deploying for the evaluation and treatment of frequent concussive brain injuries during more recent conflicts, clinical neuropsychology has been at the forefront of military selection, healthcare and research. The objective of this special issue is to provide an overview of the latest clinical research relevant to military neuropsychology-some contributors address assessment and treatment issues that are relevant to current practice and others foretell the future of our field.

METHOD

We solicited papers from established researchers and issued a general call for papers for the special issue on military neuropsychology. Results: We received submissions from several authors, eleven of which are included in this issue. These submissions cover assessment and treatment issues, as well as healthcare utilization and return to duty issues. Two apparent themes are the importance of assessing, treating, and attending to comorbidities following traumatic brain injury (TBI) and future assessment techniques moving beyond traditional cognitive performance assessment.

CONCLUSIONS

The issue highlights the importance of research in clinical neuropsychology to the practice and advancement of military neuropsychology.

Neuroimaging and Neuropsychological Outcomes Following Clinician-Delivered Cognitive Training for Six Patients With Mild Brain Injury: A Multiple Case Study

Nearly half of all mild brain injury sufferers experience long-term cognitive impairment, so an important goal in rehabilitation is to address their multiple cognitive deficits to help them return to prior levels of functioning. Cognitive training, or the use of repeated mental exercises to enhance cognition, is one remediation method for brain injury. The primary purpose of this hypothesis-generating pilot study was to explore the statistical and clinical significance of cognitive changes and transfer of training to real-life functioning following 60 h of Brain Booster, a clinician-delivered cognitive training program, for six patients with mild traumatic brain injury (TBI) or non-traumatic acquired brain injury (ABI). The secondary purpose was to explore changes in functional connectivity and neural correlates of cognitive test gains following the training. We used a multiple case study design to document significant changes in cognitive test scores, overall IQ score, and symptom ratings; and we used magnetic resonance imaging (MRI) to explore trends in functional network connectivity and neural correlates of cognitive change. All cognitive test scores showed improvement with statistically significant changes on five of the seven measures (long-term memory, processing speed, reasoning, auditory processing, and overall IQ score). The mean change in IQ score was 20 points, from a mean of 108 to a mean of 128. Five themes emerged from the qualitative data analysis including improvements in cognition, mood, social identity, performance, and Instrumental Activities of Daily Living (IADLs). With MRI, we documented significant region-to-region changes in connectivity following cognitive training including those involving the cerebellum and cerebellar networks. We also found significant correlations between changes in IQ score and change in white matter integrity of bilateral corticospinal tracts (CST) and the left uncinate fasciculus. This study adds to the growing body of literature examining the effects of cognitive training for mild TBI and ABI, and to the collection of research on the benefits of cognitive training in general. Clinical Trial Registration: www.ClinicalTrials.gov, identifier NCT02918994.

Separate N-acetyl aspartyl glutamate, N-acetyl aspartate, aspartate, and glutamate quantification after pediatric mild traumatic brain injury in the acute phase

PURPOSE

To separately measure N-acetyl aspartul glutamate (NAAG), N-acetyl aspartate (NAA), aspartate (Asp), and glutamate (Glu) concentrations in white matter (WM) using J-editing techniques in patients with mild traumatic brain injury (mTBI) in the acute phase.

METHODS

Twenty-four patients with closed concussive head injury and 29 healthy volunteers were enrolled in the current study. For extended ¹ H MRS examination, patients and controls were equally divided into two subgroups. In subgroup 1 (12 patients/15 controls), NAAG and NAA concentrations were measured in WM separately with MEGA-PRESS (echo time/repetition time [TE/TR] = 140/2000 ms; δ ON NAA / δ OFF NAA = 4.84/4.38 ppm, δ ON NAAG / δ OFF NAAG = 4.61/4.15 ppm). In subgroup 2 (12 patients/14 controls), Asp and Glu concentrations were acquired with MEGA-PRESS (TE/TR = 90/2000 ms; δ ON Asp / δ OFF Asp = 3.89/5.21 ppm) and TE-averaged PRESS (TE from 35 ms to 185 ms with 2.5-ms increments; TR = 2000 ms) pulse sequences, respectively.

RESULTS

tNAA and NAAG concentrations were found to be reduced, while NAA concentrations were unchanged, after mild mTBI. Reduced Asp and elevated myo-inositol (mI) concentrations were also found.

CONCLUSION

The main finding of the study is that the tNAA signal reduction in WM after mTBI is associated with a decrease in the NAAG concentration rather than a decrease in the NAA concentration, as was thought previously. This finding highlights the importance of separating these signals, at least for WM studies, to avoid misinterpretation of the results. NAAG plays an important role in selectively activating mGluR3 receptors, thus providing neuroprotective and neuroreparative functions immediately after mTBI. NAAG shows potential for the development of new therapeutic strategies for patients with injuries of varying severity.

Chronic traumatic encephalopathy neuropathology might not be inexorably progressive or unique to repetitive neurotrauma

In the 20th century, chronic traumatic encephalopathy (CTE) was conceptualized as a neurological disorder affecting some active and retired boxers who had tremendous exposure to neurotrauma. In recent years, the two research groups in the USA who have led the field have asserted definitively that CTE is a delayed-onset and progressive neurodegenerative disease, with symptoms appearing in midlife or decades after exposure. Between 2005 and 2012 autopsy cases of former boxers and American football players described neuropathology attributed to CTE that was broad and diverse. This pathology, resulting from multiple causes, was aggregated and referred to, in toto, as the pathology ‘characteristic’ of CTE. Preliminary consensus criteria for defining the neuropathology of CTE were forged in 2015 and published in 2016. Most of the macroscopic and microscopic neuropathological findings described as characteristic of CTE, in studies published before 2016, were not included in the new criteria for defining the pathology. In the past few years, there has been steadily emerging evidence that the neuropathology described as unique to CTE may not be unique. CTE pathology has been described in individuals with no known participation in collision or contact sports and no known exposure to repetitive neurotrauma. This pathology has been reported in individuals with substance abuse, temporal lobe epilepsy, amyotrophic lateral sclerosis, multiple system atrophy, and other neurodegenerative diseases. Moreover, throughout history, some clinical cases have been described as not being progressive, and there is now evidence that CTE neuropathology might not be progressive in some individuals. Considering the current state of knowledge, including the absence of a series of validated sensitive and specific biomarkers, CTE pathology might not be inexorably progressive or specific to those who have experienced repetitive neurotrauma.