Neurophysiological and cognitive impairment following repeated sports concussion injuries in retired professional rugby league players

Return to Sports Following Sports-Related Concussion in Collision Sports: An Expert Consensus Statement Using the Modified Delphi Technique

PURPOSE

To perform a Delphi consensus for return to sports (RTS) following sports-related concussion (SRC).

METHODS

Open-ended questions in rounds 1 and 2 were answered. The results of the first 2 rounds were used to develop a Likert-style questionnaire for round 3. If agreement at round 3 was ≤80% for an item, if panel members were outside consensus or there were >30% neither agree/disagree responses, the results were carried forward into round 4. The level of agreement and consensus was defined as 90%.

RESULTS

Individualized graduated RTS protocols should be used. A normal clinical, ocular and balance examination with no more headaches, and asymptomatic exertional test allows RTS. Earlier RTS can be considered if athletes are symptom free. The Sports Concussion Assessment Tool 5 and vestibular and ocular motor screening are recognized as useful tools to assist in decision-making. Ultimately RTS is a clinical decision. Baseline assessments should be performed at both collegiate and professional level and a combination of neurocognitive and clinical tests should be used. A specific number of recurrent concussions for season-or career-ending decisions could not be determined but will affect decision making for RTS.

CONCLUSIONS

Consensus was achieved for 10 of the 25 RTS criteria: early RTS can be considered earlier than 48 to 72 hours if athletes are completely symptom-free with no headaches, a normal clinical, ocular and balance examination. A graduated RTS should be used but should be individualized. Only 2 of the 9 assessment tools were considered to be useful: Sports Concussion Assessment Tool 5 and vestibular and ocular motor screening. RTS is mainly a clinical decision. Only 31% of the baseline assessment items achieved consensus: baseline assessments should be performed at collegiate and professional levels using a combination of neurocognitive and clinical tests. The panel disagreed on the number of recurrent concussions that should be season- or career-ending.

LEVEL OF EVIDENCE

Level V, expert Opinion.

Evidence of altered corticomotor inhibition in older adults with a history of repetitive neurotrauma. A transcranial magnetic stimulation study

International concern continues regarding the association between the long-term neurophysiologic changes from repetitive neurotrauma associated with contact and collision sports. This study describes corticomotor changes in retired contact/collision sport athletes and controls, between the ages of 30 and 70 years. Retired athletes (n = 152; 49.1 ± 8.5 years) and controls (n = 72; 47.8 ± 9.5 years) were assessed using single and paired-pulse transcranial magnetic stimulation (TMS) for active motor threshold (aMT), motor evoked potential and cortical silent period duration (expressed as MEP:cSP ratio), and short- and long-interval intracortical inhibition (SICI and LICI). Motor threshold, MEP:cSP, SICI and LICI for both groups were correlated across age. Controls showed significant moderate correlations for MEP:cSP ratios at 130% (rho = 0.48, p < 0.001), 150% (rho = 0.49, p < 0.001) and 170% aMT (rho = 0.42; p < 0.001) and significant small negative correlation for SICI (rho = -0.27; p = 0.030), and moderate negative correlation for LICI (rho = -0.43; p < 0.001). Group-wise correlation analysis comparisons showed significant correlation differences between groups for 130% (p = 0.016) and 150% aMT (p = 0.009), specifically showing retired athletes were displaying increased corticomotor inhibition. While previous studies have focussed studies on older athletes (>50 years), this study is the first to characterize corticomotor differences between retired athletes and controls across the lifespan. These results, demonstrating pathophysiological differences in retired athletes across the lifespan, provide a foundation to utilise evoked potentials as a prodromal marker in supplementing neurological assessment for traumatic encephalopathy syndrome associated with contact/collision sport athletes that is currently lacking physiological biomarkers.

Lower systemic nitric oxide bioactivity, cerebral hypoperfusion and accelerated cognitive decline in formerly concussed retired rugby union players

NEW FINDINGS

What is the central question of this study? What are the molecular, cerebrovascular and cognitive biomarkers of retired rugby union players with concussion history? What is the main finding and its importance? Retired rugby players compared with matched controls exhibited lower systemic nitric oxide bioavailability accompanied by lower middle cerebral artery velocity and mild cognitive impairment. Retired rugby players are more susceptible to accelerated cognitive decline.

ABSTRACT

Following retirement from sport, the chronic consequences of prior-recurrent contact are evident and retired rugby union players may be especially prone to accelerated cognitive decline. The present study sought to integrate molecular, cerebrovascular and cognitive biomarkers in retired rugby players with concussion history. Twenty retired rugby players aged 64 ± 5 years with three (interquartile range (IQR), 3) concussions incurred over 22 (IQR, 6) years were compared to 21 sex-, age-, cardiorespiratory fitness- and education-matched controls with no prior concussion history. Concussion symptoms and severity were assessed using the Sport Concussion Assessment Tool. Plasma/serum nitric oxide (NO) metabolites (reductive ozone-based chemiluminescence), neuron specific enolase, glial fibrillary acidic protein and neurofilament light-chain (ELISA and single molecule array) were assessed. Middle cerebral artery blood velocity (MCAv, doppler ultrasound) and reactivity to hyper/hypocapnia (CVR CO 2 hyper ${\mathrm{CVR}}_{{\mathrm{CO}}_{\mathrm{2}}{\mathrm{hyper}}}$ /CVR CO 2 hypo ${\mathrm{CVR}}_{{\mathrm{CO}}_{\mathrm{2}}{\mathrm{hypo}}}$ ) were assessed. Cognition was determined using the Grooved Pegboard Test and Montreal Cognitive Assessment. Players exhibited persistent neurological symptoms of concussion (U = 109(41) , P = 0.007), with increased severity compared to controls (U = 77(41) , P < 0.001). Lower total NO bioactivity (U = 135(41) , P = 0.049) and lower basal MCAv were apparent in players (F2,39  = 9.344, P = 0.004). This was accompanied by mild cognitive impairment (P = 0.020, 95% CI, -3.95 to -0.34), including impaired fine-motor coordination (U = 141(41) , P = 0.021). Retired rugby union players with history of multiple concussions may be characterised by impaired molecular, cerebral haemodynamic and cognitive function compared to non-concussed, non-contact controls.

An Evaluation of the Emerging Techniques in Sports-Related Concussion

SUMMARY

Sports-related concussion is now in public awareness more than ever before. Investigations into underlying pathophysiology and methods of assessment have correspondingly increased at an exponential rate. In this review, we aim to highlight some of the evidence supporting emerging techniques in the fields of neurophysiology, neuroimaging, vestibular, oculomotor, autonomics, head sensor, and accelerometer technology in the setting of the current standard: clinical diagnosis and management. In summary, the evidence we reviewed suggests that (1) head impact sensors and accelerometers may detect possible concussions that would not otherwise receive evaluation; (2) clinical diagnosis may be aided by sideline vestibular, oculomotor, and portable EEG techniques; (3) clinical decisions on return-to-play eligibility are currently not sensitive at capturing the neurometabolic, cerebrovascular, neurophysiologic, and microstructural changes that biomarkers have consistently detected days and weeks after clinical clearance. Such biomarkers include heart rate variability, quantitative electroencephalography, as well as functional, metabolic, and microstructural neuroimaging. The current challenge is overcoming the lack of consistency and replicability of any one particular technique to reach consensus.

Chronic motor performance following different traumatic brain injury severity-A systematic review

Introduction

Traumatic brain injury (TBI) is now known to be a chronic disease, causing ongoing neurodegeneration and linked to increased risk of neurodegenerative motor diseases, such as Parkinson's disease and amyotrophic lateral sclerosis. While the presentation of motor deficits acutely following traumatic brain injury is well-documented, however, less is known about how these evolve in the long-term post-injury, or how the initial severity of injury affects these outcomes. The purpose of this review, therefore, was to examine objective assessment of chronic motor impairment across the spectrum of TBI in both preclinical and clinical models.

Methods

PubMed, Embase, Scopus, and PsycINFO databases were searched with a search strategy containing key search terms for TBI and motor function. Original research articles reporting chronic motor outcomes with a clearly defined TBI severity (mild, repeated mild, moderate, moderate-severe, and severe) in an adult population were included.

Results

A total of 97 studies met the inclusion criteria, incorporating 62 preclinical and 35 clinical studies. Motor domains examined included neuroscore, gait, fine-motor, balance, and locomotion for preclinical studies and neuroscore, fine-motor, posture, and gait for clinical studies. There was little consensus among the articles presented, with extensive differences both in assessment methodology of the tests and parameters reported. In general, an effect of severity was seen, with more severe injury leading to persistent motor deficits, although subtle fine motor deficits were also seen clinically following repeated injury. Only six clinical studies investigated motor outcomes beyond 10 years post-injury and two preclinical studies to 18-24 months post-injury, and, as such, the interaction between a previous TBI and aging on motor performance is yet to be comprehensively examined.

Conclusion

Further research is required to establish standardized motor assessment procedures to fully characterize chronic motor impairment across the spectrum of TBI with comprehensive outcomes and consistent protocols. Longitudinal studies investigating the same cohort over time are also a key for understanding the interaction between TBI and aging. This is particularly critical, given the risk of neurodegenerative motor disease development following TBI.

An exploratory study into the relationship between playing at home or away and concussion

PRIMARY OBJECTIVE

To investigate the effect of home and away game travel on risk of concussion across different levels of rugby union.

RESEARCH DESIGN

Exploration study across school, university, and professional rugby teams.

METHODS AND PROCEDURES

Retrospective analysis of concussion incidence and symptomology of surveillance data and prospective data collection for potential concussions via surveys. Data was collected from school rugby teams (n = 344 matches, over 2 years), a university rugby (n = 6 matches), and a professional rugby team (n = 64 matches, over two seasons).

MAIN OUTCOMES AND RESULTS

School level rugby had an increased prevalence of concussions in away matches (p = 0.02). Likewise, there was a significant increase (p < 0.05) in concussions at away matches in university rugby. In addition, the professional rug by team had significant differences in recovery times and symptoms with away fixtures, including longer recovery times (p < 0.01), more initial symptoms (p < 0.01), as well as greater and more severe symptoms at 48 hours (p < 0.05).

CONCLUSIONS

This research highlights an increased prevalence of concussion in school and university-aged rugby players away from home, as well as increased symptoms, symptom severity, and recovery times in professional rugby players.

Sport-related concussion disclosure in women's rugby-A social identity approach

Introduction

Sport-related concussion (SRC) is a risk of collision sports such as women's rugby. To support appropriate SRC diagnosis and management, an understanding of the factors that encourage SRC disclosure is necessary. To date, research has focused on ascertaining individual player knowledge and attitudes towards SRC disclosure.

Methods

We chose to investigate the potential influence of group identification effects by examining the role of social identity on SRC disclosure in elite women's rugby. Seventeen elite players from the United Kingdom and Ireland were interviewed and their transcripts thematically analysed.

Results

The data highlighted that the players shared a very strong social identity as women in rugby and were acutely aware that their experiences were different to their male counterparts. The shared social identity had both positive and negative implications for SRC disclosure. The players interviewed did not feel comfortable disclosing their symptoms to their coach and often felt that medical staff either did not listen to them or were unavailable to them. Mediators such as communication, trust in medical teams, perceived pressure, positive injury management experience, and player role models were identified.

Discussion

This research could be utilised to inform sport psychology interventions to enhance SRC disclosure in elite women's rugby.

Assessment of Somatosensory and Motor Processing Time in Retired Athletes with a History of Repeated Head Trauma

Measurement of the adverse outcomes of repeated head trauma in athletes is often achieved using tests where the comparator is ‘accuracy’. While it is expected that ex-athletes would perform worse than controls, previous studies have shown inconsistent results. Here we have attempted to address these inconsistencies from a different perspective by quantifying not only accuracy, but also motor response times. Age-matched control subjects who have never experienced head trauma (n = 20; 41.8 ± 14.4 years) where compared to two cohorts of retired contact sport athletes with a history of head trauma/concussions; one with self-reported concerns (n = 36; 45.4 ± 12.6 years), and another with no ongoing concerns (n = 19; 43.1 ± 13.5 years). Participants performed cognitive (Cogstate) and somatosensory (Cortical Metrics) testing with accuracy and motor times recorded. Transcranial magnetic stimulation (TMS) investigated corticospinal conduction and excitability. Results showed that there was little difference between groups in accuracy scores. Conversely, motor times in all but one test revealed that ex-athletes with self-reported concerns were significantly slower compared to other groups (p ranges 0.031 to <0.001). TMS latency showed significantly increased time (p = 0.008) in the group with ongoing concerns. These findings suggest that incorporating motor times is more informative than considering accuracy scores alone.

Protect the Player, Protect the Game: Reflections from Ex-Professional Rugby Union Players on Law Changes, Protective Equipment, and Duty of Care in the Professional Game

The emphasis of this study was to interview ex-professional male rugby union players (n = 23, mean age 35.5 ± 4.7 years) and discuss concussion management during their careers. In this study, two major themes were identified: (1) the duty of care to professional rugby union players by medical personnel, coaching staff, and owners of professional clubs and (2) the use of protective equipment and law changes to enhance player safety. In total, twenty-three ex-professional rugby union players were interviewed, and the majority (61%) had represented their countries at international test-level rugby. These interviews highlighted the belief that medical teams should be objective, independent entities within a professional rugby club. Furthermore, medical teams should not be in a position of being pressurised by head coaches, members of the coaching team, or club owners regarding return-to-play (RTP) protocols specific to concussion. The interviewees believed that they were pressured by coaches or members of the coaching team to play with concussion or concussive symptoms and other physical injuries. The results indicated that they had manipulated concussion testing themselves or with assistance to pass standard concussion testing protocols. The interviewees indicated that club owners have a duty of care to players even in retirement due to the high incidence of physical and mental injuries endured as a professional rugby player. Most participants indicated that a reduction in match playing time and reducing the amount of time engaged in contact training (workload volume) may assist in reducing concussion incidence. The participants suggested that changes to the current laws of the game or the use of protective equipment did not mitigate against concussion risk in the game of rugby union. The main limitation to the study is that participants had retired in the past ten years, and conditions for players may have changed. This study has highlighted that additional efforts are required by professional clubs to ensure the highest duty of care is delivered to current players and recently retired players.

Multisensory perception is not influenced by previous concussion history in retired rugby union players

BACKGROUND

To assess whether concussion history adversely affects multisensory integration, we compared susceptibility to the Sound-Induced Flash Illusion (SIFI) in retired professional rugby players compared to controls.

METHODS

Retired professional rugby players ((N = 58) and retired international rowers (N = 26) completed a self-report concussion history questionnaire and the SIFI task. Susceptibility to the SIFI (i.e., perceiving two flashes in response to one flash paired with two beeps) was assessed at three stimulus onset asynchronies (70 ms, 150 ms or 230 ms).Logistic mixed-effects regression modeling was implemented to evaluate how athlete grouping, previous concussion history and total number of years playing sport, impacted the susceptibility to the SIFI task. The statistical significance of a fixed effect of interest was determined by a likelihood ratio test.

RESULTS

Former rugby players had significantly more self-reported concussions than the rower group (p < 0.001). There was no impact of athlete grouping (i.e., retired professional rugby players and retired international rowers), years participation in elite sport or concussion history on performance in the SIFI.

CONCLUSION

A career in professional rugby, concussion history or number of years participating in professional rugby was not found to be predictive of performance on the SIFI task.

Applying the Bradford Hill Criteria for Causation to Repetitive Head Impacts and Chronic Traumatic Encephalopathy

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with a history of repetitive head impacts (RHI). CTE was described in boxers as early as the 1920s and by the 1950s it was widely accepted that hits to the head caused some boxers to become "punch drunk." However, the recent discovery of CTE in American and Australian-rules football, soccer, rugby, ice hockey, and other sports has resulted in renewed debate on whether the relationship between RHI and CTE is causal. Identifying the strength of the evidential relationship between CTE and RHI has implications for public health and medico-legal issues. From a public health perspective, environmentally caused diseases can be mitigated or prevented. Medico-legally, millions of children are exposed to RHI through sports participation; this demographic is too young to legally consent to any potential long-term risks associated with this exposure. To better understand the strength of evidence underlying the possible causal relationship between RHI and CTE, we examined the medical literature through the Bradford Hill criteria for causation. The Bradford Hill criteria, first proposed in 1965 by Sir Austin Bradford Hill, provide a framework to determine if one can justifiably move from an observed association to a verdict of causation. The Bradford Hill criteria include nine viewpoints by which to evaluate human epidemiologic evidence to determine if causation can be deduced: strength, consistency, specificity, temporality, biological gradient, plausibility, coherence, experiment, and analogy. We explored the question of causation by evaluating studies on CTE as it relates to RHI exposure. Through this lens, we found convincing evidence of a causal relationship between RHI and CTE, as well as an absence of evidence-based alternative explanations. By organizing the CTE literature through this framework, we hope to advance the global conversation on CTE mitigation efforts.

A non-invasive biomechanical model of mild TBI in larval zebrafish

A mild traumatic brain injury is a neurological dysfunction caused by biomechanical forces transmitted to the brain in physical impacts. The current understanding of the neuropathological cascade resulting in the manifested clinical signs and symptoms is limited due to the absence of sensitive brain imaging methods. Zebrafish are established models for the reproduction and study of neurobiological pathologies. However, all available models mostly recreate moderate-to-severe focal injuries in adult zebrafish. The present work has induced a mild brain trauma in larval zebrafish through a non-invasive biomechanical approach. A custom-made apparatus with a commercially available motor was employed to expose larvae to rapidly decelerating linear movements. The neurophysiological changes following concussion were assessed through behavioural quantifications of startle reflex locomotor distance and habituation metrics. Here we show that the injury was followed, within five minutes, by a transient anxiety state and CNS dysfunction manifested by increased startle responsivity with impaired startle habituation, putatively mirroring the human clinical sign of hypersensitivity to noise. Within a day after the injury, chronic effects arose, as evidenced by an overall reduced responsivity to sensory stimulation (lower amplitude and distance travelled along successive stimuli), reflecting the human post-concussive symptomatology. This study represents a step forward towards the establishment of a parsimonious (simple, less ethically concerning, yet sensitive) animal model of mild TBI. Our behavioural findings mimic aspects of acute and chronic effects of human concussion, which warrant further study at molecular, cellular and circuit levels. While our model opens wide avenues for studying the underlying cellular and molecular pathomechanisms, it also enables high-throughput testing of therapeutic interventions to accelerate post-concussive recovery.

Concussion-Associated Polygenic Profiles of Elite Male Rugby Athletes

Due to the high-velocity collision-based nature of elite rugby league and union, the risk of sustaining a concussion is high. Occurrence of and outcomes following a concussion are probably affected by the interaction of multiple genes in a polygenic manner. This study investigated whether suspected concussion-associated polygenic profiles of elite rugby athletes differed from non-athletes and between rugby union forwards and backs. We hypothesised that a total genotype score (TGS) using eight concussion-associated polymorphisms would be higher in elite rugby athletes than non-athletes, indicating selection for protection against incurring or suffering prolonged effects of, concussion in the relatively high-risk environment of competitive rugby. In addition, multifactor dimensionality reduction was used to identify genetic interactions. Contrary to our hypothesis, TGS did not differ between elite rugby athletes and non-athletes (p ≥ 0.065), nor between rugby union forwards and backs (p = 0.668). Accordingly, the TGS could not discriminate between elite rugby athletes and non-athletes (AUC ~0.5), suggesting that, for the eight polymorphisms investigated, elite rugby athletes do not have a more ‘preferable’ concussion-associated polygenic profile than non-athletes. However, the COMT (rs4680) and MAPT (rs10445337) GC allele combination was more common in rugby athletes (31.7%; p < 0.001) and rugby union athletes (31.8%; p < 0.001) than non-athletes (24.5%). Our results thus suggest a genetic interaction between COMT (rs4680) and MAPT (rs10445337) assists rugby athletes in achieving elite status. These findings need exploration vis-à-vis sport-related concussion injury data and could have implications for the management of inter-individual differences in concussion risk.

Mild traumatic brain injury impairs the coordination of intrinsic and motor-related neural dynamics

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MTBI is poorly understood and lacks objective diagnostic and prognostic tools.

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Abnormal neural oscillations are found in subjects with a history of mTBI.

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We identify transient bursts in MEG data using a Hidden Markov Model.

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We explain a deficit in beta connectivity and power in terms of transient bursts.

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Data-driven feature selection identifies symptom-relevant functional connections.

Mild traumatic brain injury (mTBI) poses a considerable burden on healthcare systems. Whilst most patients recover quickly, a significant number suffer from sequelae that are not accompanied by measurable structural damage. Understanding the neural underpinnings of these debilitating effects and developing a means to detect injury, would address an important unmet clinical need. It could inform interventions and help predict prognosis. Magnetoencephalography (MEG) affords excellent sensitivity in probing neural function and presents significant promise for assessing mTBI, with abnormal neural oscillations being a potential specific biomarker. However, growing evidence suggests that neural dynamics are (at least in part) driven by transient, pan-spectral bursting and in this paper, we employ this model to investigate mTBI. We applied a Hidden Markov Model to MEG data recorded during resting state and a motor task and show that previous findings of diminished intrinsic beta amplitude in individuals with mTBI are largely due to the reduced beta band spectral content of bursts, and that diminished beta connectivity results from a loss in the temporal coincidence of burst states. In a motor task, mTBI results in diminished burst amplitude, altered modulation of burst probability during movement, and a loss in connectivity in motor networks. These results suggest that, mechanistically, mTBI disrupts the structural framework underlying neural synchrony, which impairs network function. Whilst the damage may be too subtle for structural imaging to see, the functional consequences are detectable and persist after injury. Our work shows that mTBI impairs the dynamic coordination of neural network activity and proposes a potent new method for understanding mTBI.

White matter abnormalities in active elite adult rugby players

The recognition, diagnosis and management of mild traumatic brain injuries are difficult and confusing. It is unclear how the severity and number of injuries sustained relate to brain injuries, such as diffuse axonal injury, diffuse vascular injury and progressive neurodegeneration. Advances in neuroimaging techniques enable the investigation of neuropathologies associated with acute and long-term effects of injury. Head injuries are the most commonly reported injury seen during professional rugby. There is increased vigilance for the immediate effects of these injuries in matches, but there has been surprisingly little research investigating the longer-term effects of rugby participation. Here, we present a longitudinal observational study investigating the relationship of exposure to rugby participation and sub-acute head injuries in professional adult male and female rugby union and league players using advanced MRI. Diffusion tensor imaging and susceptibility weighted imaging was used to assess white matter structure and evidence of axonal and diffuse vascular injury. We also studied changes in brain structure over time using Jacobian Determinant statistics extracted from serial volumetric imaging. We tested 41 male and 3 female adult elite rugby players, of whom 21 attended study visits after a head injury, alongside 32 non-sporting controls, 15 non-collision-sport athletic controls and 16 longitudinally assessed controls. Eighteen rugby players participated in the longitudinal arm of the study, with a second visit at least 6 months after their first scan. Neuroimaging evidence of either axonal injury or diffuse vascular injury was present in 23% (10/44) of players. In the non-acutely injured group of rugby players, abnormalities of fractional anisotropy and other diffusion measures were seen. In contrast, non-collision-sport athletic controls were not classified as showing abnormalities. A group level contrast also showed evidence of sub-acute injury using diffusion tensor imaging in rugby players. Examination of longitudinal imaging revealed unexpected reductions in white matter volume in the elite rugby players studied. These changes were not related to self-reported head injury history or neuropsychological test scores and might indicate excess neurodegeneration in white matter tracts affected by injury. Taken together, our findings suggest an association of participation in elite adult rugby with changes in brain structure. Further well-designed large-scale studies are needed to understand the impact of both repeated sports-related head impacts and head injuries on brain structure, and to clarify whether the abnormalities we have observed are related to an increased risk of neurodegenerative disease and impaired neurocognitive function following elite rugby participation.

The Neurological Consequences of Engaging in Australian Collision Sports

Collision sports are an integral part of Australian culture. The most common collision sports in Australia are Australian rules football, rugby union, and rugby league. Each of these sports often results in participants sustaining mild brain traumas, such as concussive and subconcussive injuries. However, the majority of previous studies and reviews pertaining to the neurological implications of sustaining mild brain traumas, while engaging in collision sports, have focused on those popular in North America and Europe. As part of this 2020 International Neurotrauma Symposium special issue, which highlights Australian neurotrauma research, this article will therefore review the burden of mild brain traumas in Australian collision sports athletes. Specifically, this review will first provide an overview of the consequences of mild brain trauma in Australian collision sports, followed by a summary of the previous studies that have investigated neurocognition, ocular motor function, neuroimaging, and fluid biomarkers, as well as neuropathological outcomes in Australian collision sports athletes. A review of the literature indicates that although Australians have contributed to the field, several knowledge gaps and limitations currently exist. These include important questions related to sex differences, the identification and implementation of blood and imaging biomarkers, the need for consistent study designs and common data elements, as well as more multi-modal studies. We conclude that although Australia has had an active history of investigating the neurological impact of collision sports participation, further research is clearly needed to better understand these consequences in Australian athletes and how they can be mitigated.

Diffusion MRI as a complementary assessment to cognition, emotion, and motor dysfunction after sports-related concussion: a systematic review and critical appraisal of the literature

Sports-related concussion (SRC) is a complex and heterogeneous injury with psychological, cognitive and functional consequences. Advances in diffusion magnetic resonance imaging (dMRI) allow sensitive measurement of white matter pathology post-SRC and may provide insight into injury and recovery. We systematically reviewed and meta-analyzed the literature examining dMRI alongside cognitive, emotional or motor assessments to determine relationships between these analyses. Sixteen studies examining young athletes (n = 6) or retired professionals (n = 10) met the inclusion criteria, with 12 emotional, 10 cognitive and four motor assessments. Studies had heterogeneous methodology, moderate quality and modest sample sizes. Fractional anisotropy (FA) was the most frequent dMRI metric, with SRC-induced changes described most commonly in the frontal lobe and least in the cerebellum and brainstem. There is an emerging complementary role for dMRI as part of a comprehensive assessment battery for SRC. However, larger-scale studies with broader subject populations (specifically, in females and in the 30-45 year age range) are needed to corroborate findings and determine the true diagnostic utility of dMRI post-SRC.

The Expanding Role of Quantitative Pupillometry in the Evaluation and Management of Traumatic Brain Injury

Traumatic brain injury is a rapidly increasing source of morbidity and mortality across the world. As such, the evaluation and management of traumatic brain injuries ranging from mild to severe are under active investigation. Over the last two decades, quantitative pupillometry has been increasingly found to be useful in both the immediate evaluation and ongoing management of traumatic brain injured patients. Given these findings and the portability and ease of use of modern pupillometers, further adoption and deployment of quantitative pupillometers into the preclinical and hospital settings of both resource rich and medically austere environments.

Assessing Clinical Change in Individuals Exposed to Repetitive Head Impacts: The Repetitive Head Impact Composite Index

Background: There is a current lack of any composite measure for the effective tracking and monitoring of clinical change in individuals exposed to repetitive head impacts (RHI). The aim of this study is to create a composite instrument for the purposes of detecting change over time in cognitive and behavioral function in individuals exposed to RHI. Methods: The data to derive the composite instrument came from the Professional Fighters Brain Health Study (PFBHS), a longitudinal study of active and retired professional fighters [boxers and mixed martial arts (MMA) fighters] and healthy controls. Participants in the PFBHS underwent assessment on an annual basis that included computerized cognitive testing and behavioral questionnaires. Multivariate logistic regression models were employed to compare active fighters (n = 117) with controls (n = 22), and retired fighters (n = 26) with controls to identify the predictors that could be used to differentiate the groups over time. In a second step, linear discriminant analysis was performed to derive the linear discriminant coefficients for the three groups by using the predictors from the two separate logistic regression models. Results: The composite scale is a weighted linear value of 12 standardized scores consisting of both current and yearly change scores in domains including: processing speed, choice reaction time, semantic fluency, letter fluency, and Barrett Impulsiveness Scale. Because the weighting of values differed between active and retired fighters, two versions emerged. The mean and standard deviation ratio (MSDR) showed that the new index had better sensitivity compared to the individual measures, with the ratio of MSDR of the new index to that of the existing measures of at least 1.84. Conclusion: With the increasing need for tools to follow individuals exposed to RHI and the potential of clinical trials on the horizon for CTE, the RHICI is poised to serve as an initial approach to a composite clinical measure.

Cumulative Sport-Related Injuries and Longer Term Impact in Retired Male Elite- and Amateur-Level Rugby Code Athletes and Non-contact Athletes: A Retrospective Study

Background

Rugby union and rugby league are popular team contact sports, but they bring a high risk of injury. Although previous studies have reported injury occurrence across one or several seasons, none have explored the total number of injuries sustained across an entire career. As the first to do so, the aim of this study was to report on cumulative injuries and their perceived long-term impact in retired rugby code athletes compared to athletes from non-contact sports.

Methods

One hundred and eighty-nine former rugby code athletes (rugby union n = 145; rugby league n = 44) and 65 former non-contact athletes were recruited to the UK Rugby Health Project between September 2016 and December 2018. Details on sports participation, sports injuries and concussion history, sports injury-related surgeries, and previous and current health were obtained from a validated, online self-report questionnaire.

Results

Former elite rugby code athletes (n = 83) reported more total injuries per player (median 39, IQR 35) than former amateur rugby code athletes (n = 106; median 23, IQR 30; p = 0.014) and non-contact sports athletes (n = 65; median 7.5, IQR 15; p < 0.001). Concussion was the most frequently reported injury for the elite and amateur rugby code groups, followed by upper/lower back and knee ligament injuries. These injuries also presented with the highest recurrence. Rugby code groups reported a higher continued impact of previous concussion, neck injuries, shoulder dislocation, ACL tears, and knee ligament injuries (p = 0.003–0.045). The reported prevalence of osteoarthritis was more than twofold greater in the elite rugby code group than in non-contact athletes (51% v 22%, p < 0.001). The prevalence of back pain and/or severe and regular joint pain was high across all groups (47–80%), particularly the elite rugby code group. The total number of joint injuries and sport injury-related surgeries was higher in those who reported current osteoarthritis and current severe and regular joint pain (p < 0.001–p = 0.028).

Conclusion

Across multiple injury types, past participation in rugby union and rugby league, particularly at elite level, is associated with a high cumulative injury load and a continued impact of previous injuries post-retirement. Given the high number of reported concussions (and their recurrence) and associations between previous injuries during a player’s career and current musculoskeletal conditions, efforts should be prioritized to reduce the occurrence and recurrence of injuries in rugby codes at all levels of the sport. Strategies should also be developed for supporting the specific physical health needs of rugby code athletes post-retirement.

Electronic supplementary material

The online version of this article (10.1007/s40279-020-01310-y) contains supplementary material, which is available to authorized users.

Chronic Neurophysiological Effects of Repeated Head Trauma in Retired Australian Male Sport Athletes

Aim: This study investigated the somatosensory and corticomotor physiology of retired contact sport athletes with a history of repeated concussion/subconcussion head trauma. Methods: Retired male athletes with a history of playing contact sports and repeated head trauma (n = 122) were divided into two groups: those who expressed concerns regarding their mental and cognitive health ("symptomatic": n = 83), and those who did not express any ongoing concerns ("asymptomatic": n = 39). Both groups were compared to age-matched male controls (n = 50) with no history of concussions or participation in contact sports, an absence of self-reported cognitive, or mood impairments. Transcranial magnetic stimulation (TMS) and vibrotactile stimulation were used to assess corticomotor and somatosensory pathways respectively. TMS and vibrotactile stimulation were correlated to self-reported responses using the Fatigue and Related Symptom Survey. Linear regression was used to associate concussion history with TMS, somatosensory variables. Results: Significant differences were found in symptom survey scores between all groups (p < 0.001). TMS showed significant differences between the "symptomatic" and control groups for intracortical inhibition and paired pulse TMS measures. Somatosensory measures showed significant differences for reaction time (p < 0.01) and reaction time variability (p < 0.01) between the "symptomatic" group to the "asymptomatic" and control groups. For other somatosensory measures, the "symptomatic" measures showed differences to the "control" group. Correlations showed significant associations between severity of symptom reporting with TMS and somatosensory measure, and regression revealed the number of concussions reported was shown to have significant relationships to increased intracortical inhibition and poorer somatosensory performance. Conclusion: This study shows that retired contact sport athletes expressing chronic symptoms showed significant pathophysiology compared to those with no ongoing concerns and non-concussed controls. Further, there is a linear dose-response relationship between number of reported concussions and abnormal neurophysiology. Neurophysiological assessments such as TMS and somatosensory measures represent useful and objective biomarkers to assess cortical impairments and progression of neuropsychological impairment in individuals with a history of repeated head trauma.

Examination of Reaction Time Deficits Following Concussion: A Systematic Review and Meta-analysis

BACKGROUND

Reaction time (RT) deficits are reported following concussion, but it is unknown when these deficits normalize to pre-injury status. It is also unclear how factors such as RT measurement technique and participant characteristics influence post-concussion RT.

OBJECTIVE

The purpose of this systematic review and meta-analysis was to (1) characterize acute post-concussion (0-3 days) RT impairments, (2) examine RT recovery over time, and (3) explore moderating factors related to acute RT impairment following concussion.

METHODS

Database searches (PubMed, CINAHL, EBSCOhost) were conducted according to PRISMA guidelines for articles published in English from January 2002 to March 2019. Studies compared baseline-to-post-injury RT within individuals (within-subject) and/or RT in concussed individuals to non-concussed controls (between-subject). Sixty studies met inclusion criteria, reporting on a total of 9688 participants with 214 discrete RT effects (Hedges' d; between-subject: N = 29, k = 129; within-subject: N = 42, k = 85). Of the 214 effects, 93 occurred in the acute (0-3 days) post-injury timeframe (k = 47 between-subject). Numerous demographic [sex, age, concussion history, population type (athlete, military, and general population), athlete level (high school, college), and sport], and method-based (RT test and measure type, computerized neurocognitive testing platform, concussion definition, and time post-injury) moderators were examined for mean effect influence. Mixed-effects multi-level modeling with restricted-maximum-likelihood estimation was used to account for nested effects and high heterogeneity for the pooled effect size (D+).

RESULTS

Significant medium-magnitude RT deficits were observed acutely for between- (D+ = - 0.7279, 95% CI - 0.9919, - 0.4639, I² = 88.66, p < 0.0001) and within-subject (D+ = - 0.7472, 95% CI - 0.9089, - 0.5855, I² = 89.21, p < 0.0001) effect models. RT deficits were present at the sub-acute and intermediate-term timeframes for between-subject effects (sub-acute: D+ = - 0.5655, 95% CI - 0.6958, - 0.4352, p < 0.0001; intermediate-term: D+ = - 0.3219, 95% CI - 0.5988, - 0.0450, p = 0.0245). No significant RT mean effect was observed for the between-subject model at the long-term timeframe, indicating RT recovery among concussed participants relative to controls (D+ = 0.3505, 95% CI - 0.4787, 1.1797, p = 0.3639). Sex was a significant moderator for between-subject effects, with every 1% male sample size increase demonstrating - 0.0171 (95% CI - 0.0312, - 0.0029, p = 0.0193) larger RT deficits. Within-subject effect models resulted in RT measure type (simple: [D+ = - 0.9826] vs. mixed: [D+ = - 0.6557], p = 0.0438) and computerized neurocognitive testing platforms (ANAM: [D+ = - 0.3735] vs. HeadMinder CRI: [D+ = - 1.4799] vs. ImPACT: [D+ = - 0.6749], p = 0.0004) having significantly different RT-deficit magnitudes. No other moderators produced significantly different RT-deficit magnitudes (between-subject: [p ≥ 0.0763], within-subject: [p ≥ 0.1723]).

CONCLUSIONS

Robust RT deficits were observed acutely following concussion. Minimal magnitude differences were noted when comparing between- and within-subject effects, suggesting that pre-injury baselines may not add clinical value in determining post-injury RT impairment. RT deficits persisted up till the intermediate-term (21-59 days post-injury) timeframe and indicate lingering deficits exist. Mean effect size differences were observed between RT measure types and computerized neurocognitive testing platforms; however, all categories displayed negative effects consistent with impaired RT following concussion. Clinical interpretation suggests that measuring RT post-concussion is more important than considering the RT method employed so long as reliable and valid tools are used. PROSPERO Registration #CRD42019119323.

A Systematic Review of Long-Interval Intracortical Inhibition as a Biomarker in Neuropsychiatric Disorders

Long-interval intracortical inhibition (LICI) is a paired-pulse transcranial magnetic stimulation (TMS) paradigm mediated in part by gamma-aminobutyric acid receptor B (GABA_B) inhibition. Prior work has examined LICI as a putative biomarker in an array of neuropsychiatric disorders. This review conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) sought to examine existing literature focused on LICI as a biomarker in neuropsychiatric disorders. There were 113 articles that met the inclusion criteria. Existing literature suggests that LICI may have utility as a biomarker of GABA_B functioning but more research with increased methodologic rigor is needed. The extant LICI literature has heterogenous methodology and inconsistencies in findings. Existing findings to date are also non-specific to disease. Future research should carefully consider existing methodological weaknesses and implement high-quality test-retest reliability studies.

Neurocognitive performance and mental health of retired female football players compared to non-contact sport athletes

Background

Adverse long-term effects of playing football due to repetitive head impact exposure on neurocognition and mental health are controversial. To date, no studies have evaluated such effects in women.

Aims

To (1) compare neurocognitive performance, cognitive symptoms and mental health in retired elite female football players (FB) with retired elite female non-contact sport athletes (CON), and to (2) assess whether findings are related to history of concussion and/or heading exposure in FB.

Methods

Neurocognitive performance, mental health and cognitive symptoms were assessed using computerised tests (CNS-vital signs), paper pen tests (Category fluency, Trail-Making Test, Digit Span, Paced Auditory Serial Addition Test), questionnaires (Hospital Anxiety and Depression Scale, SF-36v2 Health Survey) and a symptom checklist. Heading exposure and concussion history were self-reported in an online survey and in a clinical interview, respectively. Linear regression was used to analyse the effect of football, concussion and heading exposure on outcomes adjusted for confounders.

Results

FB (n=66) performed similar to CON (n=45) on neurocognitive tests, except for significantly lower scores on verbal memory (mean difference (MD)=−7.038, 95% CI −12.98 to –0.08, p=0.038) and verbal fluency tests (MD=−7.534, 95% CI –13.75 to –0.46, p=0.016). Among FB weaker verbal fluency performance was significantly associated with ≥2 concussions (MD=−10.36, 95% CI –18.48 to –2.83, p=0.017), and weaker verbal memory performance with frequent heading (MD=−9.166, 95% CI –17.59 to –0.123, p=0.041). The depression score differed significantly between study populations, and was significantly associated with frequent heading but not with history of concussion in FB.

Conclusion

Further studies should investigate the clinical relevance of our findings and whether the observed associations point to a causal link between repetitive head impacts and verbal memory/fluency or mental health.

Examining the Subacute Effects of Mild Traumatic Brain Injury Using a Traditional and Computerized Neuropsychological Test Battery

This study investigates subacute cognitive effects of mild traumatic brain injury (MTBI) in the Trondheim Mild TBI Study, as measured, in part, by the neuropsychological test battery of the Collaborative European NeuroTrauma Effectiveness Research in TBI (CENTER-TBI) program, including computerized tests from the Cambridge Neuropsychological Test Automated Battery (CANTAB) and traditional paper-and-pencil tests. We investigated whether cognitive function was associated with injury severity: intracranial traumatic lesions on neuroimaging, witnessed loss of consciousness (LOC), or post-traumatic amnesia (PTA) >1 h. Further, we explored which of the tests in the CENTER-TBI battery might be associated with the largest subacute effects of MTBI (i.e., at 2 weeks post-injury). We recruited 177 patients with MTBI (16-59 years of age) from a regional trauma center and an outpatient clinic,79 trauma control participants, and 81 community control participants. The MTBI group differed from community controls only on one traditional test of processing speed (coding; p = 0.009, Cliff's delta [Δ] = 0.20). Patients with intracranial abnormalities performed worse than those without on a traditional test (phonemic verbal fluency; p = 0.043, Δ = 0.27), and patients with LOC performed differently on the Attention Switching Task from the CANTAB (p = 0.020, Δ = -0.20). Patients with PTA >1 h performed worse than those with <1 h on 10 measures, from traditional tests and the CANTAB (Δ = 0.33-0.20), likely attributable, at least in part, to pre-existing differences in intellectual functioning between groups. In general, those with MTBI had good neuropsychological outcome 2 weeks after injury and no particular CENTER-TBI computerized or traditional tests seemed to be more sensitive to subtle cognitive deficits.

Use of the King-Devick test for the identification of concussion in an amateur domestic women's rugby union team over two competition seasons in New Zealand

OBJECTIVE

To investigate the use of the King-Devick (K-D) test for sideline assessment of concussive injuries in a New Zealand amateur women's rugby union team.

DESIGN

Prospective cohort observational.

METHODS

All players were K-D tested during pre-season using a tablet (iPad; Apple Inc., Cupertino, CA). Differences in K-D scores and test-retest reliability were calculated for baseline test scores, baseline, and post-injury (concussion) sideline assessment and baseline and post-season testing scores for tests by year and as a combined score.

RESULTS

One training-related (0.3 per 1000 training-hrs) and nine match-related (16.1 per 1000 match-hrs) concussions were recorded. The K-D post-injury (concussion) sideline test score were significantly slower than established baseline (-4.4 [-5.8 to -3.4] s; χ²₍₁₎ = 42.2; p < 0.0001; t₍₉₎ = -4.0; p = 0.0029; d = -0.8). There was good-to-excellent reliability of the K-D test for baseline (ICC: 0.84 to 0.89), post-injury (concussion) sideline assessment (ICC: 0.82 to 0.97) and post-season evaluation (ICC: 0.79 to 0.83).

DISCUSSION

By utilising the baseline to post-injury (concussion) assessment comparisons, any player with a post-injury (concussion) assessment slowing of their K-D test time, regardless of whether the player has, or has not had a witnessed insult, should be withheld from any further participation until they are evaluated by a medical professional trained in the management of concussion.

CONCLUSION

This study has provided additional evidence to support the use of the K-D test as a frontline method of assessing concussion with good to excellent reliability of the test for baseline, side-line assessment and post-season evaluation.

Altered motor system function in post-concussion syndrome as assessed via transcranial magnetic stimulation

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Study examining corticospinal and cortical activity in post-concussion.

•

Reduction in GABAB-mediated inhibition observed.

•

These changes were associated with depression-related symptoms.

Objective

It is unclear why specific individuals incur chronic symptoms following a concussion. This exploratory research aims to identify and characterize any neurophysiological differences that may exist in motor cortex function in post-concussion syndrome (PCS).

Methods

Fifteen adults with PCS and 13 healthy, non-injured adults were tested. All participants completed symptom questionnaires, and transcranial magnetic stimulation (TMS) was used to measure intracortical and transcallosal excitability and inhibition in the dominant motor cortex.

Results

Cortical silent period (p = 0.02, g = 0.96) and ipsilateral silent period (p = 0.04, g = 0.78) were shorter in the PCS group compared to the control group which may reflect reduced GABA-mediated inhibition in PCS. Furthermore, increased corticomotor excitability was observed in the left hemisphere but not the right hemisphere.

Conclusions

These data suggest that persistent neurophysiological differences are present in those with PCS. The exact contributing factors to such changes remain to be investigated by future studies.

Significance

This study provides novel evidence of lasting neurophysiological changes in PCS.

The Neurophysiological Responses of Concussive Impacts: A Systematic Review and Meta-Analysis of Transcranial Magnetic Stimulation Studies

Aim: This systematic review and meta-analysis investigated neurophysiological responses using transcranial magnetic stimulation (TMS) following a concussion or sub-concussion.

Methods: A systematic searching of relevant databases for peer-reviewed literature quantifying motor evoked potentials from TMS between 1999 and 2019 was performed. A meta-analysis quantified pooled data for measures including motor threshold, motor latency, and motor evoked potential amplitude and for inhibitory measures such as cortical silent period duration, short-interval intracortical inhibition (SICI), and long-interval intracortical inhibition (LICI) ratios.

Results: Fifteen articles met the inclusion criteria. The studies were arbitrarily classified into the groups, based on time post-concussion, “acute” (subjects 0–3 months post-injury, n = 8) and “post-acute” (3 months−2 years post-concussion, n = 7). A TMS quality of study checklist rated studies from moderate to high in methodological quality; however, the risk of bias analysis found that the included studies were categorised as high risk of bias, particularly for a lack of allocation concealment and blinding of participants in the methodologies. A meta-analysis showed no differences in excitability measures, apart from a decreased motor threshold that was observed in the concussed group (SMD −0.28, 95% CI −0.51 to −0.04; P = 0.02) for the post-acute time frame. Conversely, all inhibitory measures showed differences between groups. Cortical silent period duration was found to be significantly increased in the acute (SMD 1.19, 95% CI 0.58–1.81; P < 0.001) and post-acute (SMD 0.55, 95% CI 0.12–0.98; P = 0.01) time frames. The SICI (SMD −1.15, 95% CI −1.95 to −0.34; P = 0.005) and LICI (SMD −1.95, 95% CI −3.04 to −0.85; P = 0.005) ratios were reduced, inferring increased inhibition, for the post-acute time frame.

Conclusion: This systematic review and meta-analysis demonstrates that inhibitory pathways are affected in the acute period post-concussion. However, persistent alterations in cortical excitability remain, with increased intracortical inhibition. While TMS should be considered as a reliable technique to measure the functional integrity of the central nervous system, the high risk of bias and heterogeneity in data suggest that future studies should aim to incorporate standardised methodological techniques, particularly with threshold determination and stimulus intervals for paired-pulse measures.

Developing Cognition Endpoints for the CENTER-TBI Neuropsychological Test Battery

Background: Measuring cognitive functioning is common in traumatic brain injury (TBI) research, but no universally accepted method for combining several neuropsychological test scores into composite, or summary, scores exists. This study examined several possible composite scores for the test battery used in the large-scale study Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury (CENTER-TBI).

Methods: Participants with mild traumatic brain injury (MTBI; n = 140), orthopedic trauma (n = 72), and healthy community controls (n = 70) from the Trondheim MTBI follow-up study completed the CENTER-TBI test battery at 2 weeks after injury, which includes both traditional paper-and-pencil tests and tests from the Cambridge Neuropsychological Test Automated Battery (CANTAB). Seven composite scores were calculated for the paper and pencil tests, the CANTAB tests, and all tests combined (i.e., 21 composites): the overall test battery mean (OTBM); global deficit score (GDS); neuropsychological deficit score-weighted (NDS-W); low score composite (LSC); and the number of scores ≤5th percentile, ≤16th percentile, or <50th percentile.

Results: The OTBM and the number of scores <50th percentile composites had distributional characteristics approaching a normal distribution. The other composites were in general highly skewed and zero-inflated. When the MTBI group, the trauma control group, and the community control group were compared, effect sizes were negligible to small for all composites. Subgroups with vs. without loss of consciousness at the time of injury did not differ on the composite scores and neither did subgroups with complicated vs. uncomplicated MTBIs. Intercorrelations were high within the paper-and-pencil composites, the CANTAB composites, and the combined composites and lower between the paper-and-pencil composites and the CANTAB composites.

Conclusion: None of the composites revealed significant differences between participants with MTBI and the two control groups. Some of the composite scores were highly correlated and may be redundant. Additional research on patients with moderate to severe TBIs is needed to determine which scores are most appropriate for TBI clinical trials.

Cognitive Ageing in Top-Level Female Soccer Players Compared to a Normative Sample from the General Population: A Cross-sectional Study

OBJECTIVE

There is an ongoing debate on the potential negative effect of contact sport participation on long-term neurocognitive performance due to inherent exposure to concussive and subconcussive head impacts. The aim of the present study was to investigate whether cognitive ageing is exacerbated in elite soccer players compared to the general population.

METHOD

Neurocognitive performance in 6 domains was compared between 240 elite soccer players and a normative sample from the general population (n = 585) using the computerised test battery CNS Vital Signs. We used two-way factorial ANOVA to analyse the interaction between age groups (15-19, 20-29, 30-39, 40-49 years) and study population (female soccer players vs. norm sample) in their effects on neurocognitive performance.

RESULTS

We found no significant interaction effect of age group and study population in five of six test domains. For processing speed, the effect of age was more pronounced in female soccer players (F = 16.89, p = .002). Further, there was a clear main effect of study population on neurocognitive performance with generally better scores in soccer players.

CONCLUSIONS

Elite female soccer players generally performed better than the norm sample on tests of cognitive function, and further, cognitive ageing effects were similar in elite soccer players and controls in all but one domain. A lifespan approach may facilitate insightful future research regarding questions related to long-term neurocognitive health in contact sport athletes.

History of Sport-Related Concussion and Long-Term Clinical Cognitive Health Outcomes in Retired Athletes: A Systematic Review

BACKGROUND

Sport-related concussions (SRCs) are known to have short-term effects on cognitive processes, which can result in diverse clinical presentations. The long-term effects of SRC and repeated exposure to head impacts that do not result in SRC on specific cognitive health outcomes remain unclear.

OBJECTIVES

To synthesize and appraise the evidence base regarding cognitive health in living retired athletes with a history of head-impact exposure or SRC.

DATA SOURCES

A systematic search of the EMBASE, PsycINFO, MEDLINE/PubMed, CINAHL, Cochrane Central Register of Controlled Trials, and Web of Science databases was conducted from inception to April 2018 using common key words and medical subject headings related to 3 components: (1) the participant (eg, retired athlete), (2) the primary outcome measure (eg, cognitive test used), and (3) the secondary outcome measure (eg, history of sport concussion).

STUDY SELECTION

Cross-sectional studies of living retired male or female athletes in which at least 1 cognitive test was used as an outcome measure were included. Two reviewers independently screened studies.

DATA EXTRACTION

Data extraction was performed using Strengthening the Reporting of Observational Studies in Epidemiology guidelines. Methodologic quality was assessed independently by 2 reviewers using the Downs and Black tool.

DATA SYNTHESIS

The search yielded 46 cross-sectional observational studies that were included in a qualitative synthesis. Most included studies (80%, n = 37) were published in the 5 years before our review. A large proportion of these studies (n = 20) included retired American National Football League players. The other research investigated professional, university, high school, and amateur retired athletes participating in sports such as American and Australian football, boxing, field and ice hockey, rugby, and soccer. The total sample consisted of 13 975 participants: 7387 collision-sport athletes, 662 contact-sport athletes, 3346 noncontact-sport athletes, and 2580 participants classified as controls. Compared with control participants or normative data, retired athletes displayed worse performance in 17 of 31 studies (55%) of memory, 6 of 11 studies (55%) of executive function, and 4 of 6 studies (67%) of psychomotor function and increased subjective concerns about cognitive function in 11 of 14 studies (79%). The authors of 13 of 46 investigations (28%) reported a frequency-response relationship, with poorer cognitive outcomes in athletes who had greater levels of exposure to head impacts or concussions. However, these results must be interpreted in light of the lack of methodologic rigor and moderate quality assessment of the included studies.

CONCLUSIONS

Evidence of poorer cognitive health among retired athletes with a history of concussion and head-impact exposure is evolving. Our results suggest that a history of SRC may more greatly affect the cognitive domains of memory, executive function, and psychomotor function. Retired athletes appeared to have increased self-reported cognitive difficulties, but the paucity of high-quality, prospective studies limited the conclusions that could be drawn regarding a cause-and-effect relationship between concussion and long-term health outcomes. Future researchers should consider a range of cognitive health outcomes, as well as premorbid ability, in diverse samples of athletes with or without a history of concussion or head-impact exposure to delineate the long-term effects of sport participation on cognitive functioning.

Corticomotor correlates of somatosensory reaction time and variability in individuals with post concussion symptoms

Persistent post concussion symptoms (PPCS) describe the condition when an individual experiences chronic symptoms, particularly fatigue, beyond the expected time of recovery. The aim of this study was to quantify the effect of fatigue and related ongoing symptoms on somatosensory and corticomotor pathways using reaction time (RT) testing, and single-pulse and paired-pulse transcranial magnetic stimulation (TMS). Eighty-three participants (nine female, mean age 37.9 ± 11.5 years) were divided into two groups (persistent symptoms versus asymptomatic) following self-report based upon previously published clinical symptom scores. All participants completed somatosensory and visuomotor RT testing, as well as corticomotor excitability and inhibition measurements via TMS. Participants in the persistent symptom group (n = 38) reported greater number of previous concussions (t = 2.81, p = 0.006) and significantly higher levels of fatigue and related symptoms in the asymptomatic group (n = 45; t = 11.32, p < 0.006). Somatosensory RT showed significant slowing and increased variability in the persistent symptoms group (p < 0.001), however no significant differences were observed between groups for visuomotor RTs. Transcranial magnetic stimulation revealed differences between groups for intracortical inhibition at all stimulus intensities and paired pulse measures. The results indicate that somatosensory and corticomotor systems reflect on-going fatigue. From a practical perspective, objective and simplistic measures such as somatosensory and corticomotor measures can be used in the assessment of PPCS and gauging the efficacy of post concussion rehabilitation programmes.

Long-Term Cognitive Performance of Retired Athletes with Sport-Related Concussion: A Systematic Review and Meta-Analysis

Objective: The purpose of this systematic review is to quantitatively estimate (or invest) the impacts of sports-related concussions (SRCs) on cognitive performance among retired athletes more than 10 years after retirement. Methods: Six databases including (MEDLINE, Scopus, Web of Science, SPORTDiscus, CINAHL, and PsycArtilces) were employed to retrieve the related studies. Studies that evaluate the association between cognitive function and the SRC of retired athletes sustaining more than 10 years were included. Results: A total of 11 studies that included 792 participants (534 retired athletes with SRC) were identified. The results indicated that the retired athletes with SRCs, compared to the non-concussion group, had significant cognitive deficits in verbal memory (SMD = -0.29, 95% CI -0.59 to -0.02, I² = 52.8%), delayed recall (SMD = -0.30, 95% CI -0.46 to 0.07, I² = 27.9%), and attention (SMD = -0.33, 95% CI -0.59 to -0.06, I² = 0%). Additionally, meta-regression demonstrated that the period of time between testing and the last concussion is significantly associated with reduced verbal memory (β = -0.03681, p = 0.03), and increasing age is significantly associated with the verbal memory (β = -0.03767, p = 0.01), immediate recall (β = -0.08684, p = 0.02), and delay recall (β = -0.07432, p = 0.02). Conclusion: The retired athletes who suffered from SRCs during their playing career had declined cognitive performance in partial domains (immediate recall, visuospatial ability, and reaction time) later in life.

Neurophysiological abnormalities in individuals with persistent post-concussion symptoms

Concussion injury results in a rapid onset of transient neurological impairment that can resolve quickly, or sometimes evolve over time, but usually resolve within seven to 10 days. However, a small but noticeable cohort (~10%) of individuals continues to experience persistent lingering effects, particularly fatigue, recognized as post-concussion symptoms (PCS). This study explored neurophysiological mechanisms in people with persistent PCS. Studies involved using self-report post-concussion fatigue scale, transcranial magnetic stimulation (TMS) and somatosensory stimulation in those with diagnosed PCS (n = 20; 36.1 ± 14.0 yr., 4 female; mean time post-concussion 15.4 ± 7.6 months) to fully recovered individuals (n = 20; 33.8 ± 6.6 yr., 2 female; post-concussion 12.9 ± 6.6 months) and healthy controls (n = 20; 37.7 ± 8.0 yr., 3 female). PCS participants demonstrated a significantly higher self-report fatigue (score: PCS 20.2 [95% CI 17.4-22.9], Recovered 6.2 [3.1-9.3], Control 2.75 [0.6-4.8]). PCS participants showed a worsening of reaction time (F_2,57 = 4.214; p = 0.020) and increased reaction time variability (F_2,57 = 5.505; p = 0.007). Somatosensory differences were observed for amplitude discrimination (F_2,57 = 5.166; p = 0.009), temporal order judgment (F_2,57 = 4.606; p = 0.014) and duration discrimination (F_2,57 = 6.081; p = 0.004). Increased intracortical inhibition in TMS single pulse suprathreshold stimulation (110%: F_2,57 = 6.842; p = 0.002; 130%: F_2,57 = 4.900; p = 0.011; 150%: F_2,57 = 4.638; p = 0.014; 170%: F_2,57 = 9.845; p < 0.001) and paired pulse protocols was also seen (SICI: F_2,57 = 23.390; p < 0.001, and LICI: F_2,57 = 21.603; p < 0.001). Using non-invasive stimulation techniques, this novel study showed increased cortical inhibition and compromised central information processing, suggesting neural mechanisms underpinning ongoing fatigue, allowing for potential clinical rehabilitation strategies.