Chronic traumatic encephalopathy: a critical appraisal

A case of cognitive impairment in an ex-boxer

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease related to the long-term consequences of repetitive cranial trauma. However, the CTE clinical phenotype has yet to be clearly defined. A 63-year-old man visited the hospital due to memory impairment. He was a former boxer. He scored 23 points on the Mini-Mental State Examination (MMSE). Magnetic resonance imaging (MRI) of the brain showed mild hippocampal atrophy. Reduced perfusion is identified in the bilateral frontal and parietotemporal lobes in cerebral blood flow on single photon emission computed tomography (SPECT). From detailed history taking, neuropsychological testing and neuroimaging, our case has not only suggestive probable CTE but also comorbid Alzheimer's disease (AD). The diagnosis process of CTE is complex; therefore, detailed longitudinal history taking, neuropsychological testing and imaging were important.

Pathophysiology and Neuroimmune Interactions Underlying Parkinson's Disease and Traumatic Brain Injury

Parkinson's disease (PD) is a progressive neurodegenerative disorder clinically defined by motor instability, bradykinesia, and resting tremors. The clinical symptomatology is seen alongside pathologic changes, most notably the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and the accumulation of α-synuclein and neuromelanin aggregates throughout numerous neural circuits. Traumatic brain injury (TBI) has been implicated as a risk factor for developing various neurodegenerative diseases, with the most compelling argument for the development of PD. Dopaminergic abnormalities, the accumulation of α-synuclein, and disruptions in neural homeostatic mechanisms, including but not limited to the release of pro-inflammatory mediators and the production of reactive oxygen species (ROS), are all present following TBI and are closely related to the pathologic changes seen in PD. Neuronal iron accumulation is discernable in degenerative and injured brain states, as is aquaporin-4 (APQ4). APQ4 is an essential mediator of synaptic plasticity in PD and regulates edematous states in the brain after TBI. Whether the cellular and parenchymal changes seen post-TBI directly cause neurodegenerative diseases such as PD is a point of considerable interest and debate; this review explores the vast array of neuroimmunological interactions and subsequent analogous changes that occur in TBI and PD. There is significant interest in exploring the validity of the relationship between TBI and PD, which is a focus of this review.

Effects of White-Matter Tract Length in Sport-Related Concussion: A Tractography Study from the NCAA-DoD CARE Consortium

Sport-related concussion (SRC) is an important public health issue. White-matter alterations after SRC are widely studied by neuroimaging approaches, such as diffusion magnetic resonance imaging (MRI). Although the exact anatomical location of the alterations may differ, significant white-matter alterations are commonly observed in long fiber tracts, but are never proven. In the present study, we performed streamline tractography to characterize the association between tract length and white-matter microstructural alterations after SRC. Sixty-eight collegiate athletes diagnosed with acute concussion (24-48 h post-injury) and 64 matched contact-sport controls were included in this study. The athletes underwent diffusion tensor imaging (DTI) in 3.0 T MRI scanners across three study sites. DTI metrics were used for tract-based spatial statistics to map white-matter regions-of-interest (ROIs) with significant group differences. Whole-brain white-mater streamline tractography was performed to extract "affected" white-matter streamlines (i.e., streamlines passing through the identified ROIs). In the concussed athletes, streamline counts and DTI metrics of the affected white-matter fiber tracts were summarized and compared with unaffected white-matter tracts across tract length in the same participant. The affected white-matter tracts had a high streamline count at length of 80-100 mm and high length-adjusted affected ratio for streamline length longer than 80 mm. DTI mean diffusivity was higher in the affected streamlines longer than 100 mm with significant associations with the Brief Symptom Inventory score. Our findings suggest that long fibers in the brains of collegiate athletes are more vulnerable to acute SRC with higher mean diffusivity and a higher affected ratio compared with the whole distribution.

Longitudinal white-matter abnormalities in sports-related concussion: A diffusion MRI study

OBJECTIVE

To study longitudinal recovery trajectories of white matter after sports-related concussion (SRC) by performing diffusion tensor imaging (DTI) on collegiate athletes who sustained SRC.

METHODS

Collegiate athletes (n = 219, 82 concussed athletes, 68 contact-sport controls, and 69 non-contact-sport controls) were included from the Concussion Assessment, Research and Education Consortium. The participants completed clinical assessments and DTI at 4 time points: 24 to 48 hours after injury, asymptomatic state, 7 days after return-to-play, and 6 months after injury. Tract-based spatial statistics was used to investigate group differences in DTI metrics and to identify white-matter areas with persistent abnormalities. Generalized linear mixed models were used to study longitudinal changes and associations between outcome measures and DTI metrics. Cox proportional hazards model was used to study effects of white-matter abnormalities on recovery time.

RESULTS

In the white matter of concussed athletes, DTI-derived mean diffusivity was significantly higher than in the controls at 24 to 48 hours after injury and beyond the point when the concussed athletes became asymptomatic. While the extent of affected white matter decreased over time, part of the corpus callosum had persistent group differences across all the time points. Furthermore, greater elevation of mean diffusivity at acute concussion was associated with worse clinical outcome measures (i.e., Brief Symptom Inventory scores and symptom severity scores) and prolonged recovery time. No significant differences in DTI metrics were observed between the contact-sport and non-contact-sport controls.

CONCLUSIONS

Changes in white matter were evident after SRC at 6 months after injury but were not observed in contact-sport exposure. Furthermore, the persistent white-matter abnormalities were associated with clinical outcomes and delayed recovery time.

Preventive potential of low intensity pulsed ultrasound for chronic traumatic encephalopathy after repetitive head collisions in contact sports

Chronic traumatic encephalopathy (CTE), a disease process well-recognized in boxers, American football players and military personnel, is a progressive neurodegenerative disease caused by repetitive blows to the head. Subjects with CTE can have a wide range of emotional, cognitive and physical symptoms. The cognitive group patients had a significantly higher probability of developing dementia in later years. Currently, there are no disease modifying regimen for CTE. Timely intervention of head blow could diminish the development of CTE. Low-intensity pulsed ultrasound (LIPUS) is a common adjunct used to promote bone healing for fresh fracture. Recent reports suggest that LIPUS can noninvasively modulate the cortical function and have neuroprotective effect in various animal models of traumatic brain injury, stroke, Alzheimer's disease and major depressive disorder. The multifunctional mechanisms of LIPUS neuroprotective effect include several trophic factor stimulations, anti-inflammatory properties and reduction of brain edema. From the above evidence, LIPUS intervention could be a strategy for the prevention of the clinical CTE sequelae of repetitive head blows. We hypothesized that due to its neuroprotective effects, the non-invasive and easy-to-use method of LIPUS brain stimulation could have a preventive effect on players who have head blows during the match. The development of a time sensitive protocol, resembling the therapeutic algorithm for traumatic brain injury, would potentially prevent the development of subsequent CTE adverse outcome. Further long-term longitudinal studies of LIPUS stimulation are warranted to verify the prevention efficacy of this intervention for CTE.

Management of chronic traumatic encephalopathy

Introduction: Chronic Traumatic Encephalopathy (CTE) is a neuropathological disease defined by perivascular hyperphosphorylated tau protein depositions in a patchy distribution at the depths of cortical sulci in the brain. Presently, in living individuals, it cannot be precisely diagnosed or differentiated from other neurodegenerative diseases nor are there treatments for the underlying disease process. There are non-pharmacologic and pharmacologic treatments for the symptoms of CTE that improve the quality of daily life. That is the primary focus of this review article that used Pub Med and other standard databases but drew heavily from the author's personal experience managing patients at risk for CTE. Areas covered: The history and pathology of CTE, aiding the clinician diagnosing CTE as unlikely, possible, or probable in the living, and symptom treatment are the major areas discussed. Expert opinion: Diagnosing CTE during life with sensitive and specific biomarkers is the next critical step and only then will its incidence and prevalence, risk factors, and clinical features due to tauopathy versus axonopathy or other features be known.

Hybrid Diffusion Imaging in Mild Traumatic Brain Injury

Mild traumatic brain injury (mTBI) is an important public health problem. Although conventional medical imaging techniques can detect moderate-to-severe injuries, they are relatively insensitive to mTBI. In this study, we used hybrid diffusion imaging (HYDI) to detect white matter alterations in 19 patients with mTBI and 23 other trauma control patients. Within 15 days (standard deviation = 10) of brain injury, all subjects underwent magnetic resonance HYDI and were assessed with a battery of neuropsychological tests of sustained attention, memory, and executive function. Tract-based spatial statistics (TBSS) was used for voxel-wise statistical analyses within the white matter skeleton to study between-group differences in diffusion metrics, within-group correlations between diffusion metrics and clinical outcomes, and between-group interaction effects. The advanced diffusion imaging techniques, including neurite orientation dispersion and density imaging (NODDI) and q-space analyses, appeared to be more sensitive then classic diffusion tensor imaging. Only NODDI-derived intra-axonal volume fraction (V_ic) demonstrated significant group differences (i.e., 5–9% lower in the injured brain). Within the mTBI group, V_ic and a q-space measure, P₀, correlated with 6 of 10 neuropsychological tests, including measures of attention, memory, and executive function. In addition, the direction of correlations differed significantly between groups (R² > 0.71 and p_interation < 0.03). Specifically, in the control group, higher V_ic and P₀ were associated with better performances on clinical assessments, whereas in the mTBI group, higher V_ic and P₀ were associated with worse performances with correlation coefficients >0.83. In summary, the NODDI-derived axonal density index and q-space measure for tissue restriction demonstrated superior sensitivity to white matter changes shortly after mTBI. These techniques hold promise as a neuroimaging biomarker for mTBI.

The Biological Basis of Chronic Traumatic Encephalopathy following Blast Injury: A Literature Review

The United States Department of Defense Blast Injury Research Program Coordinating Office organized the 2015 International State-of-the-Science meeting to explore links between blast-related head injury and the development of chronic traumatic encephalopathy (CTE). Before the meeting, the planning committee examined articles published between 2005 and October 2015 and prepared this literature review, which summarized broadly CTE research and addressed questions about the pathophysiological basis of CTE and its relationship to blast- and nonblast-related head injury. It served to inform participants objectively and help focus meeting discussion on identifying knowledge gaps and priority research areas. CTE is described generally as a progressive neurodegenerative disorder affecting persons exposed to head injury. Affected individuals have been participants primarily in contact sports and military personnel, some of whom were exposed to blast. The symptomatology of CTE overlaps with Alzheimer's disease and includes neurological and cognitive deficits, psychiatric and behavioral problems, and dementia. There are no validated diagnostic criteria, and neuropathological evidence of CTE has come exclusively from autopsy examination of subjects with histories of exposure to head injury. The perivascular accumulation of hyperphosphorylated tau (p-tau) at the depths of cortical sulci is thought to be unique to CTE and has been proposed as a diagnostic requirement, although the contribution of p-tau and other reported pathologies to the development of clinical symptoms of CTE are unknown. The literature on CTE is limited and is focused predominantly on head injuries unrelated to blast exposure (e.g., football players and boxers). In addition, comparative analyses of clinical case reports has been challenging because of small case numbers, selection biases, methodological differences, and lack of matched controls, particularly for blast-exposed individuals. Consequently, the existing literature is not sufficient to determine whether the development of CTE is associated with head injury frequency (e.g., single vs. multiple exposures) or head injury type (e.g., impact, nonimpact, blast-related). Moreover, the incidence and prevalence of CTE in at-risk populations is unknown. Future research priorities should include identifying additional risk factors, pursuing population-based longitudinal studies, and developing the ability to detect and diagnose CTE in living persons using validated criteria.

Alzheimer's disease and chronic traumatic encephalopathy: Distinct but possibly overlapping disease entities

BACKGROUND

Alzheimer's disease (AD) and chronic traumatic encephalopathy (CTE) have long been recognized as sharing some similar neuropathological features, mainly the presence of neurofibrilary tangles and hyperphosphorylated tau, but have generally been described as distinct entities. Evidence indicates that neurotrauma increases the risk of developing dementia and accelerates the progression of disease. Findings are emerging that CTE and AD may be present in the same patients.

CLINICAL PRESENTATION

This study presents a series of previously unpublished cases, with one case demonstrating possible neurotrauma-related AD, one pure CTE, and an example of a case exhibiting features of both AD and CTE. The future significance of this work lies not only in the confirmation of AD-CTE co-existence, but, more importantly, ways of generating a hypothesis about the possibility that CTE may accelerate AD development. Understanding the relationship between neurotrauma and neurodegenerative disease will help elucidate how distinct disease entities can co-exist in the same patient. It will ultimately require the use of pre-clinical animal models and repeat injury paradigms to investigate clinically relevant injury mechanisms. These models should produce a CTE-like phenotype that must be both neuropathologically and behaviourally similar to human disease.

CONCLUSION

This case series and review of the literature presents a discussion of AD and CTE in the context of neurotrauma. It highlights recent work from repetitive neurotrauma models with an emphasis on those exhibiting a CTE-like phenotype. Potential mechanisms of interest shared amongst AD and CTE are briefly addressed and future experiments are advocated for to enhance understanding of CTE pathophysiology and the relationship between CTE and AD.

Chronic Exposure to Androgenic-Anabolic Steroids Exacerbates Axonal Injury and Microgliosis in the CHIMERA Mouse Model of Repetitive Concussion

Concussion is a serious health concern. Concussion in athletes is of particular interest with respect to the relationship of concussion exposure to risk of chronic traumatic encephalopathy (CTE), a neurodegenerative condition associated with altered cognitive and psychiatric functions and profound tauopathy. However, much remains to be learned about factors other than cumulative exposure that could influence concussion pathogenesis. Approximately 20% of CTE cases report a history of substance use including androgenic-anabolic steroids (AAS). How acute, chronic, or historical AAS use may affect the vulnerability of the brain to concussion is unknown. We therefore tested whether antecedent AAS exposure in young, male C57Bl/6 mice affects acute behavioral and neuropathological responses to mild traumatic brain injury (TBI) induced with the CHIMERA (Closed Head Impact Model of Engineered Rotational Acceleration) platform. Male C57Bl/6 mice received either vehicle or a cocktail of three AAS (testosterone, nandrolone and 17α-methyltestosterone) from 8-16 weeks of age. At the end of the 7th week of treatment, mice underwent two closed-head TBI or sham procedures spaced 24 h apart using CHIMERA. Post-repetitive TBI (rTBI) behavior was assessed for 7 d followed by tissue collection. AAS treatment induced the expected physiological changes including increased body weight, testicular atrophy, aggression and downregulation of brain 5-HT1B receptor expression. rTBI induced behavioral deficits, widespread axonal injury and white matter microgliosis. While AAS treatment did not worsen post-rTBI behavioral changes, AAS-treated mice exhibited significantly exacerbated axonal injury and microgliosis, indicating that AAS exposure can alter neuronal and innate immune responses to concussive TBI.

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.

Alpha-synuclein as a pathological link between chronic traumatic brain injury and Parkinson's disease

The long-term consequences of traumatic brain injury (TBI) are closely associated with the development of histopathological deficits. Notably, TBI may predispose long-term survivors to age-related neurodegenerative diseases, such as Parkinson's disease (PD), which is characterized by a gradual degeneration of the nigrostriatal dopaminergic neurons. However, preclinical studies on the pathophysiological changes in substantia nigra (SN) after chronic TBI are lacking. In the present in vivo study, we examined the pathological link between PD-associated dopaminergic neuronal loss and chronic TBI. Sixty days post-TBI, rats were euthanized and brain tissues harvested. Immunostaining was performed using tyrosine hydroxylase (TH), an enzyme required for the synthesis of dopamine in neurons, α-synuclein, a presynaptic protein that plays a role in synaptic vesicle recycling, and major histocompatibility complex II (MHCII), a protein found in antigen presenting cells such as inflammatory microglia cells, all key players in PD pathology. Unbiased stereology analyses revealed significant decrease of TH-positive expression in the surviving dopaminergic neurons of the SN pars compacta (SNpc) relative to sham control. In parallel, increased α-synuclein accumulation was detected in the ipsilateral SN compared to the contralateral SN in TBI animals or sham control. In addition, exacerbation of MHCII+ cells was recognized in the SN and cerebral peduncle ipsilateral to injury relative to contralateral side and sham control. These results suggest α-synuclein as a pathological link between chronic effects of TBI and PD symptoms as evidenced by significant overexpression and abnormal accumulation of α-synuclein in inflammation-infiltrated SN of rats exposed to chronic TBI. J. Cell. Physiol. 230: 1024–1032, 2015. © 2014 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.

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.

Chronic traumatic encephalopathy: historical origins and current perspective

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease that is most often identified in postmortem autopsies of individuals exposed to repetitive head impacts, such as boxers and football players. The neuropathology of CTE is characterized by the accumulation of hyperphosphorylated tau protein in a pattern that is unique from that of other neurodegenerative diseases, including Alzheimer's disease. The clinical features of CTE are often progressive, leading to dramatic changes in mood, behavior, and cognition, frequently resulting in debilitating dementia. In some cases, motor features, including parkinsonism, can also be present. In this review, the historical origins of CTE are revealed and an overview of the current state of knowledge of CTE is provided, including the neuropathology, clinical features, proposed clinical and pathological diagnostic criteria, potential in vivo biomarkers, known risk factors, and treatment options.