The spectrum of disease in chronic traumatic encephalopathy

Imaging in Chronic Traumatic Encephalopathy and Traumatic Brain Injury

Context:

The diagnosis of chronic traumatic encephalopathy (CTE) can only be made pathologically, and there is no concordance of defined clinical criteria for premorbid diagnosis. The absence of established criteria and the insufficient imaging findings to detect this disease in a living athlete are of growing concern.

Evidence Acquisition:

The article is a review of the current literature on CTE. Databases searched include Medline, PubMed, JAMA evidence, and evidence-based medicine guidelines Cochrane Library, Hospital for Special Surgery, and Cornell Library databases.

Study Design:

Clinical review.

Level of Evidence:

Level 4.

Results:

Chronic traumatic encephalopathy cannot be diagnosed on imaging. Examples of imaging findings in common types of head trauma are discussed.

Conclusion:

Further study is necessary to correlate the clinical and imaging findings of repetitive head injuries with the pathologic diagnosis of CTE.

Chronic traumatic encephalopathy: A paradigm in search of evidence?

Chronic traumatic encephalopathy (CTE) has been in the medical literature since the 1920s. It is characterized clinically by diverse neuropsychiatric symptoms, and pathologically by variable degrees of phosphorylated tau accumulation in the brain. The evolving paradigm for the pathogenesis of CTE suggests that concussion or subconcussion from athletic participation initiates a cascade of pathologic events, encompassing neuroinflammation and protein templating with trans-synaptic neurotoxicity. The end result is neurologic and neurobehavioral deterioration, often with self-harm. Although these concepts warrant further investigation, the available evidence permits no conclusions as regards the pathogenesis of the reported findings. Investigations into the role of premorbid or co-morbid neurodegenerative diseases has been limited to date, and in-depth genetic analyses have not been performed. The role of concussion or subconcussion if any, whether and how the condition progresses over time, the extent of phosphorylated tau in clinically normal athletes, the role of phosphorylated tau as a toxic species versus an inert disease response, and whether protein templating has any in vivo relevance remain to be elucidated.

Rugby contact and collisions--clinical challenges of a global game

Rugby Union (rugby) is a sport that evolved from and resembles other forms of football but is unique in many respects and presents distinctive clinical challenges. This article discusses those aspects of rugby that are different from other sports and those injuries that have specific significance to the game as a result of it being a global collision sport with an increasing focus on serious injury prevention. Injury screening and intervention programs, neck injuries, rugby's contribution to evolving concussion protocols, contact and travel-related illnesses, and rugby's drug intervention protocols are discussed.

Cognitive function and brain structure after recurrent mild traumatic brain injuries in young-to-middle-aged adults

Recurrent mild traumatic brain injuries (mTBIs) are regarded as an independent risk factor for developing dementia in later life. We here aimed to evaluate associations between recurrent mTBIs, cognition, and gray matter volume and microstructure as revealed by structural magnetic resonance imaging (MRI) in the chronic phase after mTBIs in young adulthood. We enrolled 20 young-to-middle-aged subjects, who reported two or more sports-related mTBIs, with the last mTBI > 6 months prior to study enrolment (mTBI group), and 21 age-, sex- and education matched controls with no history of mTBI (control group). All participants received comprehensive neuropsychological testing, and high resolution T1-weighted and diffusion tensor MRI in order to assess cortical thickness (CT) and microstructure, hippocampal volume, and ventricle size. Compared to the control group, subjects of the mTBI group presented with lower CT within the right temporal lobe and left insula using an a priori region of interest approach. Higher number of mTBIs was associated with lower CT in bilateral insula, right middle temporal gyrus and right entorhinal area. Our results suggest persistent detrimental effects of recurrent mTBIs on CT already in young-to-middle-aged adults. If additional structural deterioration occurs during aging, subtle neuropsychological decline may progress to clinically overt dementia earlier than in age-matched controls, a hypothesis to be assessed in future prospective trials.

Transplantation of human oligodendrocyte progenitor cells in an animal model of diffuse traumatic axonal injury: survival and differentiation

Introduction

Diffuse axonal injury is an extremely common type of traumatic brain injury encountered in motor vehicle crashes, sports injuries, and in combat. Although many cases of diffuse axonal injury result in chronic disability, there are no current treatments for this condition. Its basic lesion, traumatic axonal injury, has been aggressively modeled in primate and rodent animal models. The inexorable axonal and perikaryal degeneration and dysmyelination often encountered in traumatic axonal injury calls for regenerative therapies, including therapies based on stem cells and precursors. Here we explore the proof of concept that treatments based on transplants of human oligodendrocyte progenitor cells can replace or remodel myelin and, eventually, contribute to axonal regeneration in traumatic axonal injury.

Methods

We derived human oligodendrocyte progenitor cells from the human embryonic stem cell line H9, purified and characterized them. We then transplanted these human oligodendrocyte progenitor cells into the deep sensorimotor cortex next to the corpus callosum of nude rats subjected to traumatic axonal injury based on the impact acceleration model of Marmarou. We explored the time course and spatial distribution of differentiation and structural integration of these cells in rat forebrain.

Results

At the time of transplantation, over 90 % of human oligodendrocyte progenitor cells expressed A2B5, PDGFR, NG2, O4, Olig2 and Sox10, a profile consistent with their progenitor or early oligodendrocyte status. After transplantation, these cells survived well and migrated massively via the corpus callosum in both injured and uninjured brains. Human oligodendrocyte progenitor cells displayed a striking preference for white matter tracts and were contained almost exclusively in the corpus callosum and external capsule, the striatopallidal striae, and cortical layer 6. Over 3 months, human oligodendrocyte progenitor cells progressively matured into myelin basic protein(+) and adenomatous polyposis coli protein(+) oligodendrocytes. The injured environment in the corpus callosum of impact acceleration subjects tended to favor maturation of human oligodendrocyte progenitor cells. Electron microscopy revealed that mature transplant-derived oligodendrocytes ensheathed host axons with spiral wraps intimately associated with myelin sheaths.

Conclusions

Our findings suggest that, instead of differentiating locally, human oligodendrocyte progenitor cells migrate massively along white matter tracts and differentiate extensively into ensheathing oligodendrocytes. These features make them appealing candidates for cellular therapies of diffuse axonal injury aiming at myelin remodeling and axonal protection or regeneration.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0087-0) contains supplementary material, which is available to authorized users.

Tau PET imaging in Alzheimer's disease

In several neurodegenerative diseases that are collectively called tauopathies, progressive accumulation of tau in the brain is closely associated with neurodegeneration and cognitive impairment. Noninvasive detection of tau protein deposits in the brain would be useful to diagnose tauopathies as well as to track and predict disease progression. Recently, several tau PET tracers including T807, THK-5117, and PBB3 have been developed and succeeded in imaging neurofibrillary pathology in vivo. For use of tau PET as a biomarker of tau pathology in Alzheimer's disease, PET tracers should have high affinity to PHF-tau and high selectivity for tau over amyloid-β and other protein deposits. PET tau imaging enables the longitudinal assessment of the spatial pattern of tau deposition and its relation to amyloid-β pathology and neurodegeneration. This technology could also be applied to the pharmacological assessment of anti-tau therapy, thereby allowing preventive interventions.

Myelin and oligodendrocyte lineage cells in white matter pathology and plasticity after traumatic brain injury

Impact to the head or rapid head acceleration-deceleration can cause traumatic brain injury (TBI) with a characteristic pathology of traumatic axonal injury (TAI) and secondary damage in white matter tracts. Myelin and oligodendrocyte lineage cells have significant roles in the progression of white matter pathology after TBI and in the potential for plasticity and subsequent recovery. The myelination pattern of specific brain regions, such as frontal cortex, may also increase susceptibility to neurodegeneration and psychiatric symptoms after TBI. White matter pathology after TBI depends on the extent and distribution of axon damage, microhemorrhages and/or neuroinflammation. TAI occurs in a pattern of damaged axons dispersed among intact axons in white matter tracts. TAI accompanied by bleeding and/or inflammation produces focal regions of overt tissue destruction, resulting in loss of both axons and myelin. White matter regions with TAI may also exhibit demyelination of intact axons. Demyelinated axons that remain viable have the potential for remyelination and recovery of function. Indeed, animal models of TBI have demonstrated demyelination that is associated with evidence of remyelination, including oligodendrocyte progenitor cell proliferation, generation of new oligodendrocytes, and formation of thinner myelin. Changes in neuronal activity that accompany TBI may also involve myelin remodeling, which modifies conduction efficiency along intact myelinated fibers. Thus, effective remyelination and myelin remodeling may be neurobiological substrates of plasticity in neuronal circuits that require long-distance communication. This perspective integrates findings from multiple contexts to propose a model of myelin and oligodendrocyte lineage cell relevance in white matter injury after TBI. This article is part of the Special Issue entitled 'Oligodendrocytes in Health and Disease'.

Disruption of caudate working memory activation in chronic blast-related traumatic brain injury

Mild to moderate traumatic brain injury (TBI) due to blast exposure is frequently diagnosed in veterans returning from the wars in Iraq and Afghanistan. However, it is unclear whether neural damage resulting from blast TBI differs from that found in TBI due to blunt-force trauma (e.g., falls and motor vehicle crashes). Little is also known about the effects of blast TBI on neural networks, particularly over the long term. Because impairment in working memory has been linked to blunt-force TBI, the present functional magnetic resonance imaging (fMRI) study sought to investigate whether brain activation in response to a working memory task would discriminate blunt-force from blast TBI. Twenty-five veterans (mean age = 29.8 years, standard deviation = 6.01 years, 1 female) who incurred TBI due to blast an average of 4.2 years prior to enrollment and 25 civilians (mean age = 27.4 years, standard deviation = 6.68 years, 4 females) with TBI due to blunt-force trauma performed the Sternberg Item Recognition Task while undergoing fMRI. The task involved encoding 1, 3, or 5 items in working memory. A group of 25 veterans (mean age = 29.9 years, standard deviation = 5.53 years, 0 females) and a group of 25 civilians (mean age = 27.3 years, standard deviation = 5.81 years, 0 females) without history of TBI underwent identical imaging procedures and served as controls. Results indicated that the civilian TBI group and both control groups demonstrated a monotonic relationship between working memory set size and activation in the right caudate during encoding, whereas the blast TBI group did not (p < 0.05, corrected for multiple comparisons using False Discovery Rate). Blast TBI was also associated with worse performance on the Sternberg Item Recognition Task relative to the other groups, although no other group differences were found on neuropsychological measures of episodic memory, inhibition, and general processing speed. These results could not be attributed to caudate atrophy or the presence of PTSD symptoms. Our results point to a specific vulnerability of the caudate to blast injury. Changes in activation during the Sternberg Item Recognition Task, and potentially other tasks that recruit the caudate, may serve as biomarkers for blast TBI.

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We investigated whether fMRI would discriminate blunt-force from blast mTBI.

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We used a working memory task with varying numbers of letters (set sizes).

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Blunt-force TBI showed a monotonic relation between set size and caudate activation.

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This relation was disrupted in the blast TBI group.

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Results point to a specific vulnerability of the caudate to blast injury

A novel closed-body model of spinal cord injury caused by high-pressure air blasts produces extensive axonal injury and motor impairments

Diffuse axonal injury is thought to be the basis of the functional impairments stemming from mild traumatic brain injury. To examine how axons are damaged by traumatic events, such as motor vehicle accidents, falls, sports activities, or explosive blasts, we have taken advantage of the spinal cord with its extensive white matter tracts. We developed a closed-body model of spinal cord injury in mice whereby high-pressure air blasts targeted to lower thoracic vertebral levels produce tensile, compressive, and shear forces within the parenchyma of the spinal cord and thereby cause extensive axonal injury. Markers of cytoskeletal integrity showed that spinal cord axons exhibited three distinct pathologies: microtubule breakage, neurofilament compaction, and calpain-mediated spectrin breakdown. The dorsally situated axons of the corticospinal tract primarily exhibited microtubule breakage, whereas all three pathologies were common in the lateral and ventral white matter. Individual axons typically demonstrated only one of the three pathologies during the first 24h after blast injury, suggesting that the different perturbations are initiated independently of one another. For the first few days after blast, neurofilament compaction was frequently accompanied by autophagy, and subsequent to that, by the fragmentation of degenerating axons. TuJ1 immunolabeling and mice with YFP-reporter labeling each revealed more extensive microtubule breakage than did βAPP immunolabeling, raising doubts about the sensitivity of this standard approach for assessing axonal injury. Although motor deficits were mild and largely transient, some aspects of motor function gradually worsened over several weeks, suggesting that a low level of axonal degeneration continued past the initial wave. Our model can help provide further insight into how to intervene in the processes by which initial axonal damage culminates in axonal degeneration, to improve outcomes after traumatic injury. Importantly, our findings of extensive axonal injury also caution that repeated trauma is likely to have cumulative adverse consequences for both brain and spinal cord.

A review of neuroimaging findings in repetitive brain trauma

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease confirmed at postmortem. Those at highest risk are professional athletes who participate in contact sports and military personnel who are exposed to repetitive blast events. All neuropathologically confirmed CTE cases, to date, have had a history of repetitive head impacts. This suggests that repetitive head impacts may be necessary for the initiation of the pathogenetic cascade that, in some cases, leads to CTE. Importantly, while all CTE appears to result from repetitive brain trauma, not all repetitive brain trauma results in CTE. Magnetic resonance imaging has great potential for understanding better the underlying mechanisms of repetitive brain trauma. In this review, we provide an overview of advanced imaging techniques currently used to investigate brain anomalies. We also provide an overview of neuroimaging findings in those exposed to repetitive head impacts in the acute/subacute and chronic phase of injury and in more neurodegenerative phases of injury, as well as in military personnel exposed to repetitive head impacts. Finally, we discuss future directions for research that will likely lead to a better understanding of the underlying mechanisms separating those who recover from repetitive brain trauma vs. those who go on to develop CTE.

Association of equipment worn and concussion injury rates in National Collegiate Athletic Association football practices: 2004-2005 to 2008-2009 academic years

BACKGROUND

The epidemiology of football-related concussions has been extensively examined. However, although football players experience more at-risk exposure time during practices than competitions, there is a dearth of literature examining the nature of the activities or equipment worn during practice. In particular, varying levels of equipment worn during practices may place players at varying levels of risk for concussion.

PURPOSE

To describe the epidemiology of NCAA men's football concussions that occurred during practices from the 2004-2005 to 2008-2009 academic years by amount of equipment worn.

STUDY DESIGN

Descriptive epidemiology study.

METHODS

Men's collegiate football data from the National Collegiate Athletic Association Injury Surveillance System (NCAA ISS) during the 5-year study period were analyzed. Injury rates and injury rate ratios (RRs) were reported with 95% confidence intervals.

RESULTS

During the study period, 795 concussions were reported during practices, resulting in an injury rate of 0.39 per 1000 athlete-exposures (AEs) (95% CI, 0.36-0.42). Among NCAA divisions, Division III had the highest concussion rate (0.54/1000 AEs), followed by Division I (0.34/1000 AEs) and Division II (0.24/1000 AEs) (all P values for RRs comparing divisions<.001). Most concussions in practice occurred when players were fully padded (69.9%), followed by wearing shells (23.5%) and helmets only (1.9%). The practice concussion rate was higher in fully padded practices (0.66/1000 AEs) compared with practices when shells were worn (0.33/1000 AEs; RR=1.99 [95% CI, 1.69-2.35]; P<.001) and practices when only helmets were worn (0.03/1000 AEs; RR=22.39 [95% CI, 13.41-37.39]; P<.001). The practice concussion rate of the preseason (0.76/1000 AEs) was higher than that of the regular season (0.18/1000 AEs; RR=4.14 [95% CI, 3.55-4.83]; P<.001) and that of postseason (0.25/1000 AEs; RR=3.02 [95% CI, 1.95-4.67]; P<.001). The types of practice with the highest concussion rate were scrimmages (1.55/1000 AEs). Although only 3 concussions were sustained during scrimmage practices in which players wore shells, the concussion rate (2.84/1000 AEs) was higher than all other reported rates.

CONCLUSION

Practice concussion rates are highest during fully padded practices, preseason practices, and scrimmages, suggesting that the nature, focus, and intensity of football practices affect concussion risk. In addition, coaching staff should continue to closely monitor player safety during scrimmages. Meanwhile, future surveillance should examine whether removing scrimmages, particularly those that are not fully padded, will meaningfully reduce the incidence and rate of concussions.

Clinical features of repetitive traumatic brain injury and chronic traumatic encephalopathy

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease characterized by a distinct pattern of hyperphosphorylated tau (p-tau). Thought to be caused by repetitive concussive and subconcussive injuries, CTE is considered largely preventable. The majority of neuropathologically confirmed cases have occurred in professional contact sport athletes (eg, boxing, football). A recent post-mortem case series has magnified concerns for the public's health following its identification in six high school level athletes. CTE is diagnosed with certainty only following a post-mortem autopsy. Efforts to define the etiology and clinical progression during life are ongoing. The goal of this article is to characterize the clinical concepts associated with short- and long-term effects of repetitive traumatic brain injury, with a special emphasis on new clinical diagnostic criteria for CTE. Utilizing these new diagnostic criteria, two cases of neuropathologically confirmed CTE, one in a professional football player and one in a professional boxer, are reported. Differences in cerebellar pathology in CTE confirmed cases in boxing and football are discussed.

The neuropathology of chronic traumatic encephalopathy

Repetitive brain trauma is associated with a progressive neurological deterioration, now termed as chronic traumatic encephalopathy (CTE). Most instances of CTE occur in association with the play of sports, but CTE has also been reported in association with blast injuries and other neurotrauma. Symptoms of CTE include behavioral and mood changes, memory loss, cognitive impairment and dementia. Like many other neurodegenerative diseases, CTE is diagnosed with certainty only by neuropathological examination of brain tissue. CTE is a tauopathy characterized by the deposition of hyperphosphorylated tau (p-tau) protein as neurofibrillary tangles, astrocytic tangles and neurites in striking clusters around small blood vessels of the cortex, typically at the sulcal depths. Severely affected cases show p-tau pathology throughout the brain. Abnormalities in phosphorylated 43 kDa TAR DNA-binding protein are found in most cases of CTE; beta-amyloid is identified in 43%, associated with age. Given the importance of sports participation and physical exercise to physical and psychological health as well as disease resilience, it is critical to identify the genetic risk factors for CTE as well as to understand how other variables, such as stress, age at exposure, gender, substance abuse and other exposures, contribute to the development of CTE.

In vivo characterization of chronic traumatic encephalopathy using [F-18]FDDNP PET brain imaging

Chronic traumatic encephalopathy (CTE) is an acquired primary tauopathy with a variety of cognitive, behavioral, and motor symptoms linked to cumulative brain damage sustained from single, episodic, or repetitive traumatic brain injury (TBI). No definitive clinical diagnosis for this condition exists. In this work, we used [F-18]FDDNP PET to detect brain patterns of neuropathology distribution in retired professional American football players with suspected CTE (n = 14) and compared results with those of cognitively intact controls (n = 28) and patients with Alzheimer's dementia (AD) (n = 24), a disease that has been cognitively associated with CTE. [F-18]FDDNP PET imaging results in the retired players suggested the presence of neuropathological patterns consistent with models of concussion wherein brainstem white matter tracts undergo early axonal damage and cumulative axonal injuries along subcortical, limbic, and cortical brain circuitries supporting mood, emotions, and behavior. This deposition pattern is distinctively different from the progressive pattern of neuropathology [paired helical filament (PHF)-tau and amyloid-β] in AD, which typically begins in the medial temporal lobe progressing along the cortical default mode network, with no or minimal involvement of subcortical structures. This particular [F-18]FDDNP PET imaging pattern in cases of suspected CTE also is primarily consistent with PHF-tau distribution observed at autopsy in subjects with a history of mild TBI and autopsy-confirmed diagnosis of CTE.

Estimating Contact Exposure in Football Using the Head Impact Exposure Estimate

Over the past decade, there has been significant debate regarding the effect of cumulative subconcussive head impacts on short and long-term neurological impairment. This debate remains unresolved, because valid epidemiological estimates of athletes' total contact exposure are lacking. We present a measure to estimate the total hours of contact exposure in football over the majority of an athlete's lifespan. Through a structured oral interview, former football players provided information related to primary position played and participation in games and practice contacts during the pre-season, regular season, and post-season of each year of their high school, college, and professional football careers. Spring football for college was also included. We calculated contact exposure estimates for 64 former football players (n = 32 college football only, n = 32 professional and college football). The head impact exposure estimate (HIEE) discriminated between individuals who stopped after college football, and individuals who played professional football (p < 0.001). The HIEE measure was independent of concussion history (p = 0.82). Estimating total hours of contact exposure may allow for the detection of differences between individuals with variation in subconcussive impacts, regardless of concussion history. This measure is valuable for the surveillance of subconcussive impacts and their associated potential negative effects.

Endocannabinoids in synaptic plasticity and neuroprotection

Endocannabinoids (eCBs) are endogenous lipid mediators involved in a variety of physiological, pharmacological, and pathological processes. While activation of the eCB system primarily induces inhibitory effects on both GABAergic and glutamatergic synaptic transmission and plasticity through acting on presynaptically expressed CB1 receptors in the brain, accumulated information suggests that eCB signaling is also capable of facilitating or potentiating excitatory synaptic transmission in the hippocampus. Recent studies show that a long-lasting potentiation of excitatory synaptic transmission at Schaffer collateral (SC)-CA1 synapses is induced by spatiotemporally primed inputs, accompanying with a long-term depression of inhibitory synaptic transmission (I-LTD) in hippocampal CA1 pyramidal neurons. This input timing-dependent long-lasting synaptic potentiation at SC-CA1 synapses is mediated by 2-arachidonoylglycerol (2-AG) signaling triggered by activation of postsynaptic N-methyl-D-aspartate receptors, group I metabotropic glutamate receptors (mGluRs), and a concurrent rise in intracellular Ca(2+). Emerging evidence now also indicates that 2-AG is an important signaling mediator keeping brain homeostasis by exerting its anti-inflammatory and neuroprotective effects in response to harmful insults through CB1/2 receptor-dependent and/or -independent mechanisms. Activation of the nuclear receptor protein peroxisome proliferator-activated receptor-γ apparently is one of the important mechanisms in resolving neuroinflammation and protecting neurons produced by 2-AG signaling. Thus, the information summarized in this review suggests that the role of eCB signaling in maintaining integrity of brain function is greater than what we thought previously.

Hockey STAR: A Methodology for Assessing the Biomechanical Performance of Hockey Helmets

Optimizing the protective capabilities of helmets is one of several methods of reducing brain injury risk in sports. This paper presents the experimental and analytical development of a hockey helmet evaluation methodology. The Summation of Tests for the Analysis of Risk (STAR) formula combines head impact exposure with brain injury probability over the broad range of 227 head impacts that a hockey player is likely to experience during one season. These impact exposure data are mapped to laboratory testing parameters using a series of 12 impact conditions comprised of three energy levels and four head impact locations, which include centric and non-centric directions of force. Injury risk is determined using a multivariate injury risk function that incorporates both linear and rotational head acceleration measurements. All testing parameters are presented along with exemplar helmet test data. The Hockey STAR methodology provides a scientific framework for manufacturers to optimize hockey helmet design for injury risk reduction, as well as providing consumers with a meaningful metric to assess the relative performance of hockey helmets.

Reactive microglia drive tau pathology and contribute to the spreading of pathological tau in the brain

Pathological aggregation of tau is a hallmark of Alzheimer's disease and related tauopathies. We have previously shown that the deficiency of the microglial fractalkine receptor (CX3CR1) led to the acceleration of tau pathology and memory impairment in an hTau mouse model of tauopathy. Here, we show that microglia drive tau pathology in a cell-autonomous manner. First, tau hyperphosphorylation and aggregation occur as early as 2 months of age in hTauCx3cr1(-/-) mice. Second, CD45(+) microglial activation correlates with the spatial memory deficit and spread of tau pathology in the anatomically connected regions of the hippocampus. Third, adoptive transfer of purified microglia derived from hTauCx3cr1(-/-) mice induces tau hyperphosphorylation within the brains of non-transgenic recipient mice. Finally, inclusion of interleukin 1 receptor antagonist (Kineret®) in the adoptive transfer inoculum significantly reduces microglia-induced tau pathology. Together, our results suggest that reactive microglia are sufficient to drive tau pathology and correlate with the spread of pathological tau in the brain.

Diffusion tensor imaging findings in semi-acute mild traumatic brain injury

The past 10 years have seen a rapid increase in the use of diffusion tensor imaging to identify biomarkers of traumatic brain injury (TBI). Although the literature generally indicates decreased anisotropic diffusion at more chronic injury periods and in more severe injuries, considerable debate remains regarding the direction (i.e., increased or decreased) of anisotropic diffusion in the acute to semi-acute phase (here defined as less than 3 months post-injury) of mild TBI (mTBI). A systematic review of the literature was therefore performed to (1) determine the prevalence of different anisotropic diffusion findings (increased, decreased, bidirectional, or null) during the semi-acute injury phase of mTBI and to (2) identify clinical (e.g., age of injury, post-injury scan time, etc.) and experimental factors (e.g., number of unique directions, field strength) that may influence these findings. Results from the literature review indicated 31 articles with independent samples of semi-acute mTBI patients, with 13 studies reporting decreased anisotropic diffusion, 11 reporting increased diffusion, 2 reporting bidirectional findings, and 5 reporting null findings. Chi-squared analyses indicated that the total number of diffusion-weighted (DW) images was significantly associated with findings of either increased (DW ≥ 30) versus decreased (DW ≤ 25) anisotropic diffusion. Other clinical and experimental factors were not statistically significant for direction of anisotropic diffusion, but these results may have been limited by the relatively small number of studies within each domain (e.g., pediatric studies). In summary, current results indicate roughly equivalent number of studies reporting increased versus decreased anisotropic diffusion during semi-acute mTBI, with the number of unique diffusion images being statistically associated with the direction of findings.

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

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

Military-related traumatic brain injury and neurodegeneration

Mild traumatic brain injury (mTBI) includes concussion, subconcussion, and most exposures to explosive blast from improvised explosive devices. mTBI is the most common traumatic brain injury affecting military personnel; however, it is the most difficult to diagnose and the least well understood. It is also recognized that some mTBIs have persistent, and sometimes progressive, long-term debilitating effects. Increasing evidence suggests that a single traumatic brain injury can produce long-term gray and white matter atrophy, precipitate or accelerate age-related neurodegeneration, and increase the risk of developing Alzheimer's disease, Parkinson's disease, and motor neuron disease. In addition, repetitive mTBIs can provoke the development of a tauopathy, chronic traumatic encephalopathy. We found early changes of chronic traumatic encephalopathy in four young veterans of the Iraq and Afghanistan conflict who were exposed to explosive blast and in another young veteran who was repetitively concussed. Four of the five veterans with early-stage chronic traumatic encephalopathy were also diagnosed with posttraumatic stress disorder. Advanced chronic traumatic encephalopathy has been found in veterans who experienced repetitive neurotrauma while in service and in others who were accomplished athletes. Clinically, chronic traumatic encephalopathy is associated with behavioral changes, executive dysfunction, memory loss, and cognitive impairments that begin insidiously and progress slowly over decades. Pathologically, chronic traumatic encephalopathy produces atrophy of the frontal and temporal lobes, thalamus, and hypothalamus; septal abnormalities; and abnormal deposits of hyperphosphorylated tau as neurofibrillary tangles and disordered neurites throughout the brain. The incidence and prevalence of chronic traumatic encephalopathy and the genetic risk factors critical to its development are currently unknown. Chronic traumatic encephalopathy has clinical and pathological features that overlap with postconcussion syndrome and posttraumatic stress disorder, suggesting that the three disorders might share some biological underpinnings.

Discriminating military and civilian traumatic brain injuries

Traumatic brain injury (TBI) occurs at higher rates among service members than civilians. Explosions from improvised explosive devices and mines are the leading cause of TBI in the military. As such, TBI is frequently accompanied by other injuries, which makes its diagnosis and treatment difficult. In addition to postconcussion symptoms, those who sustain a TBI commonly report chronic pain and posttraumatic stress symptoms. This combination of symptoms is so typical they have been referred to as the "polytrauma clinical triad" among injured service members. We explore whether these symptoms discriminate civilian occurrences of TBI from those of service members, as well as the possibility that repeated blast exposure contributes to the development of chronic traumatic encephalopathy (CTE). This article is part of a Special Issue entitled 'Traumatic Brain Injury'.

Diagnosis, prognosis, and clinical management of mild traumatic brain injury

Concussion and mild traumatic brain injury (TBI) are interchangeable terms to describe a common disorder with substantial effects on public health. Advances in brain imaging, non-imaging biomarkers, and neuropathology during the past 15 years have required researchers, clinicians, and policy makers to revise their views about mild TBI as a fully reversible insult that can be repeated without consequences. These advances have led to guidelines on management of mild TBI in civilians, military personnel, and athletes, but their widespread dissemination to clinical management in emergency departments and community-based health care is still needed. The absence of unity on the definition of mild TBI, the scarcity of prospective data concerning the long-term effects of repeated mild TBI and subconcussive impacts, and the need to further develop evidence-based interventions to mitigate the long-term sequelae are areas for future research that will improve outcomes, reduce morbidity and costs, and alleviate delayed consequences that have only recently come to light.

Expert consensus document: Mind the gaps—advancing research into short-term and long-term neuropsychological outcomes of youth sports-related concussions

Sports-related concussions and repetitive subconcussive exposure are increasingly recognized as potential dangers to paediatric populations, but much remains unknown about the short-term and long-term consequences of these events, including potential cognitive impairment and risk of later-life dementia. This Expert Consensus Document is the result of a 1-day meeting convened by Safe Kids Worldwide, the Alzheimer's Drug Discovery Foundation, and the Andrews Institute for Orthopaedics and Sports Medicine. The goal is to highlight knowledge gaps and areas of critically needed research in the areas of concussion science, dementia, genetics, diagnostic and prognostic biomarkers, neuroimaging, sports injury surveillance, and information sharing. For each of these areas, we propose clear and achievable paths to improve the understanding, treatment and prevention of youth sports-related concussions.

Age of first exposure to football and later-life cognitive impairment in former NFL players

OBJECTIVE

To determine the relationship between exposure to repeated head impacts through tackle football prior to age 12, during a key period of brain development, and later-life executive function, memory, and estimated verbal IQ.

METHODS

Forty-two former National Football League (NFL) players ages 40-69 from the Diagnosing and Evaluating Traumatic Encephalopathy using Clinical Tests (DETECT) study were matched by age and divided into 2 groups based on their age of first exposure (AFE) to tackle football: AFE <12 and AFE ≥12. Participants completed the Wisconsin Card Sort Test (WCST), Neuropsychological Assessment Battery List Learning test (NAB-LL), and Wide Range Achievement Test, 4th edition (WRAT-4) Reading subtest as part of a larger neuropsychological testing battery.

RESULTS

Former NFL players in the AFE <12 group performed significantly worse than the AFE ≥12 group on all measures of the WCST, NAB-LL, and WRAT-4 Reading tests after controlling for total number of years of football played and age at the time of evaluation, indicating executive dysfunction, memory impairment, and lower estimated verbal IQ.

CONCLUSIONS

There is an association between participation in tackle football prior to age 12 and greater later-life cognitive impairment measured using objective neuropsychological tests. These findings suggest that incurring repeated head impacts during a critical neurodevelopmental period may increase the risk of later-life cognitive impairment. If replicated with larger samples and longitudinal designs, these findings may have implications for safety recommendations for youth sports.

Changes in the neurochemistry of athletes with repetitive brain trauma: preliminary results using localized correlated spectroscopy

Introduction

The goal was to identify which neurochemicals differ in professional athletes with repetitive brain trauma (RBT) when compared to healthy controls using a relatively new technology, in vivo Localized COrrelated SpectroscopY (L-COSY).

Methods

To achieve this, L-COSY was used to examine five former professional male athletes with 11 to 28 years of exposure to contact sports. Each athlete who had had multiple symptomatic concussions and repetitive sub concussive trauma during their career was assessed by an experienced neuropsychologist. All athletes had clinical symptoms including headaches, memory loss, confusion, impaired judgment, impulse control problems, aggression, and depression. Five healthy men, age and weight matched to the athlete cohort and with no history of brain trauma, were recruited as controls. Data were collected from the posterior cingulate gyrus using a 3 T clinical magnetic resonance scanner equipped with a 32 channel head coil.

Results

The variation of the method was calculated by repeated examination of a healthy control and phantom and found to be 10% and 5%, respectively, or less. The L-COSY measured large and statistically significant differences (P ≤0.05), between healthy controls and those athletes with RBT. Men with RBT showed higher levels of glutamine/glutamate (31%), choline (65%), fucosylated molecules (60%) and phenylalanine (46%). The results were evaluated and the sample size of five found to achieve a significance level P = 0.05 and a power of 90%. Differences in N-acetyl aspartate and myo-inositol between RBT and controls were small and were not statistically significance.

Conclusions

A study of a small cohort of professional athletes, with a history of RBT and symptoms of chronic traumatic encephalopathy when compared with healthy controls using 2D L-COSY, showed elevations in brain glutamate/glutamine and choline as recorded previously for early traumatic brain injury. For the first time increases in phenylalanine and fucose are recorded in the brains of athletes with RBT. Larger studies utilizing the L-COSY method may offer an in-life method of diagnosis and personalized approach for monitoring the acute effects of mild traumatic brain injury and the chronic effects of RBT.

Sodium selenate reduces hyperphosphorylated tau and improves outcomes after traumatic brain injury

Traumatic brain injury is a common and serious neurodegenerative condition that lacks a pharmaceutical intervention to improve long-term outcome. Hyperphosphorylated tau is implicated in some of the consequences of traumatic brain injury and is a potential pharmacological target. Protein phosphatase 2A is a heterotrimeric protein that regulates key signalling pathways, and protein phosphatase 2A heterotrimers consisting of the PR55 B-subunit represent the major tau phosphatase in the brain. Here we investigated whether traumatic brain injury in rats and humans would induce changes in protein phosphatase 2A and phosphorylated tau, and whether treatment with sodium selenate-a potent PR55 activator-would reduce phosphorylated tau and improve traumatic brain injury outcomes in rats. Ninety young adult male Long-Evans rats were administered either a fluid percussion injury or sham-injury. A proportion of rats were killed at 2, 24, and 72 h post-injury to assess acute changes in protein phosphatase 2A and tau. Other rats were given either sodium selenate or saline-vehicle treatment that was continuously administered via subcutaneous osmotic pump for 12 weeks. Serial magnetic resonance imaging was acquired prior to, and at 1, 4, and 12 weeks post-injury to assess evolving structural brain damage and axonal injury. Behavioural impairments were assessed at 12 weeks post-injury. The results showed that traumatic brain injury in rats acutely reduced PR55 expression and protein phosphatase 2A activity, and increased the expression of phosphorylated tau and the ratio of phosphorylated tau to total tau. Similar findings were seen in post-mortem brain samples from acute human traumatic brain injury patients, although many did not reach statistical significance. Continuous sodium selenate treatment for 12 weeks after sham or fluid percussion injury in rats increased protein phosphatase 2A activity and PR55 expression, and reduced the ratio of phosphorylated tau to total tau, attenuated brain damage, and improved behavioural outcomes in rats given a fluid percussion injury. Notably, total tau levels were decreased in rats 12 weeks after fluid percussion injury, and several other factors, including the use of anaesthetic, the length of recovery time, and that some brain injury and behavioural dysfunction still occurred in rats treated with sodium selenate must be considered in the interpretation of this study. However, taken together these data suggest protein phosphatase 2A and hyperphosphorylated tau may be involved in the neurodegenerative cascade of traumatic brain injury, and support the potential use of sodium selenate as a novel traumatic brain injury therapy.

Neurological consequences of traumatic brain injuries in sports

Traumatic brain injury (TBI) is common in boxing and other contact sports. The long term irreversible and progressive aftermath of TBI in boxers depicted as punch drunk syndrome was described almost a century ago and is now widely referred as chronic traumatic encephalopathy (CTE). The short term sequelae of acute brain injury including subdural haematoma and catastrophic brain injury may lead to death, whereas mild TBI, or concussion, causes functional disturbance and axonal injury rather than gross structural brain damage. Following concussion, symptoms such as dizziness, nausea, reduced attention, amnesia and headache tend to develop acutely but usually resolve within a week or two. Severe concussion can also lead to loss of consciousness. Despite the transient nature of the clinical symptoms, functional neuroimaging, electrophysiological, neuropsychological and neurochemical assessments indicate that the disturbance of concussion takes over a month to return to baseline and neuropathological evaluation shows that concussion-induced axonopathy may persist for years. The developing brains in children and adolescents are more susceptible to concussion than adult brain. The mechanism by which acute TBI may lead to the neurodegenerative process of CTE associated with tau hyperphosphorylation and the development of neurofibrillary tangles (NFTs) remains speculative. Focal tau-positive NFTs and neurites in close proximity to focal axonal injury and foci of microhaemorrhage and the predilection of CTE-tau pathology for perivascular and subcortical regions suggest that acute TBI-related axonal injury, loss of microvascular integrity, breach of the blood brain barrier, resulting inflammatory cascade and microglia and astrocyte activation are likely to be the basis of the mechanistic link of TBI and CTE. This article provides an overview of the acute and long-term neurological consequences of TBI in sports. Clinical, neuropathological and the possible pathophysiological mechanisms are discussed. This article is part of a Special Issue entitled 'Traumatic Brain Injury'.

Post-traumatic neurodegeneration and chronic traumatic encephalopathy

Traumatic brain injury (TBI) is a leading cause of mortality and morbidity around the world. Concussive and subconcussive forms of closed-head injury due to impact or blast neurotrauma represent the most common types of TBI in civilian and military settings. It is becoming increasingly evident that TBI can lead to persistent, long-term debilitating effects, and in some cases, progressive neurodegeneration and chronic traumatic encephalopathy (CTE). The epidemiological literature suggests that a single moderate-to-severe TBI may be associated with accelerated neurodegeneration and increased risk of Alzheimer's disease, Parkinson's disease, or motor neuron disease. However, the pathologic phenotype of these post-traumatic neurodegenerations is largely unknown and there may be pathobiological differences between post-traumatic disease and the corresponding sporadic disorder. By contrast, the pathology of CTE is increasingly well known and is characterized by a distinctive pattern of progressive brain atrophy and accumulation of hyperphosphorylated tau neurofibrillary and glial tangles, dystrophic neurites, 43 kDa TAR DNA-binding protein (TDP-43) neuronal and glial aggregates, microvasculopathy, myelinated axonopathy, neuroinflammation, and white matter degeneration. Clinically, CTE is associated with behavioral changes, executive dysfunction, memory deficits, and cognitive impairments that begin insidiously and most often progress slowly over decades. Although research on the long-term effects of TBI is advancing quickly, the incidence and prevalence of post-traumatic neurodegeneration and CTE are unknown. Critical knowledge gaps include elucidation of pathogenic mechanisms, identification of genetic risk factors, and clarification of relevant variables-including age at exposure to trauma, history of prior and subsequent head trauma, substance use, gender, stress, and comorbidities-all of which may contribute to risk profiles and the development of post-traumatic neurodegeneration and CTE. This article is part of a Special Issue entitled 'Traumatic Brain Injury'.

Epidemiology of mild traumatic brain injury and neurodegenerative disease

Every year an estimated 42 million people worldwide suffer a mild traumatic brain injury (MTBI) or concussion. More severe traumatic brain injury (TBI) is a well-established risk factor for a variety of neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis (ALS). Recently, large epidemiological studies have additionally identified MTBI as a risk factor for dementia. The role of MTBI in risk of PD or ALS is less well established. Repetitive MTBI and repetitive sub-concussive head trauma have been linked to increased risk for a variety of neurodegenerative diseases including chronic traumatic encephalopathy (CTE). CTE is a unique neurodegenerative tauopathy first described in boxers but more recently described in a variety of contact sport athletes, military veterans, and civilians exposed to repetitive MTBI. Studies of repetitive MTBI and CTE have been limited by referral bias, lack of consensus clinical criteria for CTE, challenges of quantifying MTBI exposure, and potential for confounding. The prevalence of CTE is unknown and the amount of MTBI or sub-concussive trauma exposure necessary to produce CTE is unclear. This review will summarize the current literature regarding the epidemiology of MTBI, post-TBI dementia and Parkinson's disease, and CTE while highlighting methodological challenges and critical future directions of research in this field. This article is part of a Special Issue entitled SI:Traumatic Brain Injury.

Inhibition of monoacylglycerol lipase prevents chronic traumatic encephalopathy-like neuropathology in a mouse model of repetitive mild closed head injury

Emerging evidence suggests that the risk of developing chronic traumatic encephalopathy (CTE), a progressive neurodegenerative disease, is significantly increased in military personnel and contact sports players who have been exposed to repetitive trauma brain injury (TBI). Unfortunately there are no effective medications currently available for prevention and treatment of CTE. Here we demonstrate that inhibition of monoacylglycerol lipase (MAGL), the key enzyme that metabolizes the endocannabinoid 2-arachidonoylglycerol (2-AG) in the brain, significantly reduced CTE-like neuropathologic changes in a mouse model of repetitive mild closed head injury (rmCHI). Inhibition of 2-AG metabolism promoted neurologic recovery following rmCHI and reduced proinflammatory cytokines, astroglial reactivity, expression of amyloid precursor protein and the enzymes that make Aβ, as well as formation of Aβ. Importantly, neurodegeneration, TDP-43 protein aggregation, and tau phosphorylation, which are the neuropathologic hallmarks of CTE, were significantly suppressed by MAGL inactivation. Furthermore, alterations in expression of glutamate receptor subunits and impairments in basal synaptic transmission, long-term synaptic plasticity, and spatial learning and memory were recovered by inhibition of 2-AG metabolism in animals exposed to rmCHI. Our results suggest that MAGL inhibition, which boosts 2-AG and reduces 2-AG metabolites prostaglandins in the brain, may lead to a new therapy for CTE.

Impairment of glymphatic pathway function promotes tau pathology after traumatic brain injury

Traumatic brain injury (TBI) is an established risk factor for the early development of dementia, including Alzheimer's disease, and the post-traumatic brain frequently exhibits neurofibrillary tangles comprised of aggregates of the protein tau. We have recently defined a brain-wide network of paravascular channels, termed the "glymphatic" pathway, along which CSF moves into and through the brain parenchyma, facilitating the clearance of interstitial solutes, including amyloid-β, from the brain. Here we demonstrate in mice that extracellular tau is cleared from the brain along these paravascular pathways. After TBI, glymphatic pathway function was reduced by ∼60%, with this impairment persisting for at least 1 month post injury. Genetic knock-out of the gene encoding the astroglial water channel aquaporin-4, which is importantly involved in paravascular interstitial solute clearance, exacerbated glymphatic pathway dysfunction after TBI and promoted the development of neurofibrillary pathology and neurodegeneration in the post-traumatic brain. These findings suggest that chronic impairment of glymphatic pathway function after TBI may be a key factor that renders the post-traumatic brain vulnerable to tau aggregation and the onset of neurodegeneration.

Aging, neurodegenerative disease, and traumatic brain injury: the role of neuroimaging

Traumatic brain injury (TBI) is a highly prevalent condition with significant effects on cognition and behavior. While the acute and sub-acute effects of TBI recover over time, relatively little is known about the long-term effects of TBI in relation to neurodegenerative disease. This issue has recently garnered a great deal of attention due to publicity surrounding chronic traumatic encephalopathy (CTE) in professional athletes, although CTE is but one of several neurodegenerative disorders associated with a history of TBI. Here, we review the literative on neurodegenerative disorders linked to remote TBI. We also review the evidence for neuroimaging changes associated with unhealthy brain aging in the context of remote TBI. We conclude that neuroimaging biomarkers have significant potential to increase understanding of the mechanisms of unhealthy brain aging and neurodegeneration following TBI, with potential for identifying those at risk for unhealthy brain aging prior to the clinical manifestation of neurodegenerative disease.

The pathophysiology of repetitive concussive traumatic brain injury in experimental models; new developments and open questions

In recent years, there has been an increasing interest in the pathophysiology of repetitive concussive traumatic brain injury (rcTBI) in large part due to the association with dramatic cases of progressive neurological deterioration in professional athletes, military personnel, and others. However, our understanding of the pathophysiology of rcTBI is less advanced than for more severe brain injuries. Most prominently, the mechanisms underlying traumatic axonal injury, microglial activation, amyloid-beta accumulation, and progressive tau pathology are not yet known. In addition, the role of injury to dendritic spine cytoskeletal structures, vascular reactivity impairments, and microthrombi are intriguing and subjects of ongoing inquiry. Methods for quantitative analysis of axonal injury, dendritic injury, and synaptic loss need to be refined for the field to move forward in a rigorous fashion. We and others are attempting to develop translational approaches to assess these specific pathophysiological events in both animals and humans to facilitate clinically relevant pharmacodynamic assessments of candidate therapeutics. In this article, we review and discuss several of the recent experimental results from our lab and others. We include new initial data describing the difficulty in modeling progressive tau pathology in experimental rcTBI, and results demonstrating that sertraline can alleviate social interaction deficits and depressive-like behaviors following experimental rcTBI plus foot shock stress. Furthermore, we propose a discrete set of open, experimentally tractable questions that may serve as a framework for future investigations. In addition, we also raise several important questions that are less experimentally tractable at this time, in hopes that they may stimulate future methodological developments to address them. This article is part of a Special Issue entitled "Traumatic Brain Injury".

Chronic traumatic encephalopathy in contact sports: a systematic review of all reported pathological cases

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with head trauma. Although initially believed to affect only boxers, the at-risk population has expanded to encompass a much wider demographic, including American football players, hockey players, wrestlers, and military veterans. This expansion has garnered considerable media attention and public concern for the potential neurodegenerative effects of head trauma. The main aim of this systematic review is to give a complete overview of the common findings and risk factors for CTE as well as the status quo regarding the incidence and prevalence of CTE. This systematic review was performed using PubMed and MEDLINE and includes all neuropathologically confirmed cases of CTE in the medical literature to date, from the first published case in 1954 to August 1, 2013 (n = 153). The demographics, including the primary source of mTBI (mild Traumatic Brain Injury), age and cause of death, ApoE genotype, and history of substance abuse, when listed, were obtained from each case report. The demographics of American football players found to have CTE are also presented separately in order to highlight the most prevalent group of CTE cases reported in recent years. These 153 case reports of CTE represent the largest collection to date. We found that a history of mTBI was the only risk factor consistently associated with CTE. In addition, we found no relationships between CTE and age of death or abnormal ApoE allele. Suicide and the presence of premorbid dementia was not strongly associated with CTE. We conclude that the incidence of CTE remains unknown due to the lack of large, longitudinal studies. Furthermore, the neuropathological and clinical findings related to CTE overlap with many common neurodegenerative diseases. Our review reveals significant limitations of the current CTE case reporting and questions the widespread existence of CTE in contact sports.

The Utilization of Biomechanics to Understand and Manage the Acute and Long-term Effects of Concussion

The acute and long-term effects of concussive and subconcussive head impacts on brain health have gained tremendous attention over the past five years. The treatment and management of concussion involves multiple providers from multiple disciplines and backgrounds. Varied backgrounds and approaches to assessing cognitive and motor function before and post-concussion are limiting factors in the efficient and effective management of concussion as discipline-specific rating scales and assessments serve as a barrier to effective patient hand-offs between providers. Combining principles of motor behavior with biomechanical approaches to data analysis has the potential to improve the continuity of care across the multiple providers managing athletes with concussion. Biomechanical measures have been developed and validated using mobile devices to provide objective and quantitative assessments of information processing, working memory, set switching, and postural stability. These biomechanical outcomes are integral to a clinical management algorithm, the Concussion Care Path, currently used across the Cleveland Clinic Health System. The objective outcomes provide a common data set that all providers in the spectrum of care can access which facilitates communication and the practice of medicine and in understanding the acute and long-term effects of concussion and subconcussive exposure on neurological function.