Sex differences in acute and long-term brain recovery after concussion

Using neuroimaging to identify sex differences in adults with sports-related concussion: a systematic review

Concussion is a common injury in sports that causes neurological damage, leading to memory loss and difficulty concentrating. Insufficient recovery time may result in significant long-term harm to individuals. Several neuroimaging techniques have been used to understand the pathophysiological changes following concussion, and how long individuals need to recover before returning to play. Despite the progress in neuroimaging concussion research, few studies have considered whether females sustain different effects on the brain and how recovery from concussion might differ from males. Thus, we conducted a systematic review of the existing literature to highlight sex differences in concussion with neuroimaging techniques. By searching four different databases, studies were selected if they used a neuroimaging technique to examine sex differences following concussion in athletes over the age of 18. After screening 2295 studies from an initial search, 15 were found to match the selection criteria. Nine papers established some difference between males and females, however many of these studies were not designed to specifically examine sex differences, and hence conclusions in this regard are somewhat limited. A further common limitation among these papers was a lack of whole brain scans, instead relying on regions of interest analyses, which reduces the ability to compare studies effectively. The current systematic review has highlighted the need for future studies to specifically consider whether, and how sex influences the impact and trajectory of brain recovery from concussion. This can then help to inform suitable amendments to current concussion return-to-play protocols for male and female athletes.

Evidence for Altered White Matter Organization After Mild Traumatic Brain Injury: A Scoping Review on the Use of Diffusion Magnetic Resonance Imaging and Blood-Based Biomarkers to Investigate Acute Pathology and Relationship to Persistent Post-Concussion Symptoms

Mild traumatic brain injury (mTBI) is the most common form of traumatic brain injury. Post-concussive symptoms typically resolve after a few weeks although up to 20% of people experience these symptoms for >3 months, termed persistent post-concussive symptoms (PPCS). Subtle white matter (WM) microstructural damage is thought to underlie neurological and cognitive deficits experienced post-mTBI. Evidence suggests that diffusion magnetic resonance imaging (dMRI) and blood-based biomarkers could be used as surrogate markers of WM organization. We conducted a scoping review according to PRISMA-ScR guidelines, aiming to collate evidence for the use of dMRI and/or blood-based biomarkers of WM organization, in mTBI and PPCS, and document relationships between WM biomarkers and symptoms. We focused specifically on biomarkers of axonal or myelin integrity post-mTBI. Biomarkers excluded from this review therefore included the following: astroglial, perivascular, endothelial, and inflammatory markers. A literature search performed across four databases, EMBASE, Scopus, Google Scholar, and ProQuest, identified 100 records: 68 analyzed dMRI, 28 assessed blood-based biomarkers, and 4 used both. Blood biomarker studies commonly assessed axonal cytoskeleton proteins (i.e., tau); dMRI studies assessed measures of WM organization (i.e., fractional anisotropy). Significant biomarker alterations were frequently associated with heightened symptom burden and prolonged recovery time post-injury. These data suggest that dMRI and blood-based biomarkers may be useful proxies of WM organization, although few studies assessed these complementary measures in parallel, and the relationship between modalities remains unclear. Further studies are warranted to assess the benefit of a combined biomarker approach in evaluating alterations to WM organization after mTBI.

Exploring Sex-Based Variations in Head Kinematics During Soccer Heading

While studies indicate that females experience a higher concussion risk and more severe outcomes in soccer heading compared to males, comprehensive data on the underlying factors contributing to these sex-based differences are lacking. This study investigates the sex differences in the head-to-ball impact kinematics among college-aged soccer headers in a laboratory-controlled setting. Forty subjects (20 females, 20 males) performed ten headers, and impact kinematics, including peak angular acceleration and velocity (PAA, PAV) and peak linear acceleration (PLA), were measured using mouthguards. Video recordings verified impacts and impact locations. Participants' head mass was estimated from their weights. The relationship between head mass and kinematic parameters was analyzed using Pearson correlation. The effects of head mass, sex, and impact location on kinematic parameters were assessed using MANOVA with and without head mass as a covariate. Results showed that head mass, larger in males than females, significantly affects PAA and PLA, the greater the head mass, the lower PAA and PLA. However, head mass has no effect on PAV. Females showed significantly higher PAA and PLA components but no significant differences in PAV. Impact location significantly influenced PAV, showing higher magnitudes for frontal impacts compared to top-front impacts, with no significant effects on PAA and PLA. Our results agree with epidemiological evidence that female soccer players face greater concussion risks than males, which can be attributed to their higher header-induced PAA. Future research could consider interventions like changing ball pressure, using protective headgear, and improving heading techniques to reduce high-magnitude accelerations in females.

Resting Metabolic Rate and Recovery From Sport-Related Concussion: A Critically Appraised Topic

CLINICAL SCENARIO

Critical appraisal of whole-body metabolism as a measure of concussion recovery is lacking in the available evidence. There has been extensive exploration of options for a gold standard assessment for concussion, including blood biomarkers, electroencephalogram, and neuroimaging, but none have yet to demonstrate good empirical evidence of efficacy.

CLINICAL QUESTION

In patients with sport-related concussion (SRC), can resting metabolic rate (RMR), as measured through indirect calorimetry, be used as a physiologic assessment of recovery?

SUMMARY OF KEY FINDINGS

Three studies demonstrated relevance to the clinical question. Of the selected studies, 2 studies were case-control, and 1 was a case series. All studies observed reduced total energy expenditure and increased energy balance when initially assessed between 24 and 72 hours after injury.

CLINICAL BOTTOM LINE

Evidence exists to suggest that RMR as measured with indirect calorimetry is a poor indicator of SRC recovery. All 3 articles found that RMR was not affected by SRC, even when compared with healthy controls. One article did observe a between sex difference in RMR, but a very small sample size was included in the case series.

STRENGTH OF RECOMMENDATION

The findings of this critically appraised topic suggest a strength of recommendation of grade B, demonstrating that RMR is a poor indicator of recovery from SRC.

Smirl J, Emery CA. Consequences of adolescent sport-related concussion: exploring long-term cardiorespiratory fitness and adiposity

BACKGROUND

Little is known regarding long-term consequences (≥5 years) of sport-related concussion (SRC) sustained during adolescence. Adolescent SRC has been linked to athlete considerations of sport participation and subsequent retirement from sport during this critical developmental period. Prolonged SRC symptoms can reduce ability to perform physical activity, and research suggests inactivity can extend years post-injury. Therefore, SRC may affect long-term physical activity, which may result in decreased cardiorespiratory fitness and increased adiposity.

OBJECTIVES

(1) To examine cardiorespiratory fitness, adiposity and associations with physical activity between three groups: adolescent SRC 5-15 years prior; adolescent musculoskeletal injury (MSK) 5-15 years prior; and individuals who played adolescent sport but were uninjured. (2) To explore whether biological sex-modified relationships assessed by the primary objective.

METHODS

Young adults (16-33 years old) who sustained SRC (n = 54) or MSK (n = 52) during adolescent sport and uninjured individuals (n = 50) were recruited (n = 156) from previous Sport Injury Prevention Research Centre studies and word-of-mouth. Participants completed a cycle-ergometer maximal exertion test, dual-energy X-ray absorptiometry scanning, and wore actigraphs for 1-week post-testing. Outcome measures of cardiorespiratory fitness [peak oxygen consumption (VO2peak[ml/min])] and adiposity [fat mass index (FMI)] were examined in relation to cohort, sex, time since injury, lean mass index and moderate-to-vigorous physical activity [daily MVPA (min)] via multiple linear regression.

RESULTS

In relation to the uninjured cohort, MSK (mean difference = 297.14 ml/min; β = 2.88; 95%CI: 0.99-4.76, p = 0.003) and SRC (mean difference = 268.01 ml/min; β = 2.61; 95%CI: 0.77-4.44, p = 0.006) cohorts demonstrated higher VO2peak and this did not differ based on biological sex. FMI did not differ for MSK (mean difference= -0.10 kg/m2; β= -0.02; 95%CI: -0.22-0.18, p = 0.847) or SRC (mean difference=-0.22 kg/m2; β= -0.05; 95%CI: -0.24-0.15, p = 0.642) cohorts relative to the uninjured cohort for both males and females.

CONCLUSIONS

It is possible to maintain adequate long-term cardiorespiratory fitness and adiposity following adolescent SRC relative to those who only sustained sport related MSK injuries or did not sustain significant injuries as adolescents/adults.

Missing School Days Following Sport-Related Concussion in High School Athletes

Importance

Sport-related concussions (SRC) can significantly impact students' attendance and academic performance, highlighting the importance of gradual return-to-learn protocols for recovery. Understanding the association between missed school days and recovery, especially across genders, is vital for effective concussion management in high school athletes.

Objectives

To describe missed school days in high school athletes with SRC and to determine associations between missed school days and authorized clearance to return to competition; secondarily, to determine whether school days missed differed by gender.

Design, Setting, and Participants

Cohort study among student athletes participating in athletics sponsored by the Michigan High School Athletic Association (MHSAA) during academic years 2015 to 2023. SRC was a participant eligibility criterion and was defined as a head injury during participation in a MHSAA-sanctioned event. Data were analyzed from August 2015 to June 2023.

Exposures

Primary exposure was missed school days; additional exposures included gender, year of season, concussion history, event type, sport level, contact level, and athletic trainer involvement.

Main Outcome and Measure

The primary outcome was time to full unrestricted clearance following SRC.

Results

The analysis included a total of 20 934 individuals with SRC (13 869 boys [66.25%]). Gender (χ23 = 167.40; P < .001), season (χ221 = 57.41; P < .001), event type (χ23 = 99.29; P < .001), sport level (χ29 = 68.15; P < .001), contact level (χ26 = 56.73; P < .001), and initial evaluation (χ23 = 147.13; P < .001) were independently associated with missed school days. Athletes took a median (IQR) of 11 (7-16) days to return to full unrestricted clearance. Relative to no missed school days, there was a significant mean increase of 57% (incidence rate ratio, 1.57; 95% CI, 1.52-1.62) in time to full unrestricted clearance for 3 or more missed school days. The estimated mean days to return to sport were 12.15 (95% CI, 12.00-12.30) for 0 missed school days, 12.68 (95% CI, 12.39-12.96) for 1 missed school day, 15.47 (95% CI, 15.06-15.87) for 2 missed school days, and 19.08 (95% CI, 18.55-19.62) for 3 or more missed school days.

Conclusions and Relevance

This cohort study found that high school athletes typically missed 2 or fewer school days after SRC, suggesting that concussion management teams adhered to current recommendations of 24 to 48 hours of initial rest. The dose association, with more missed school days associated with slower return to play, suggests athletes' missing more school days (eg, ≥3) may be associated with severity of concussion and warrant additional support to return to school and/or sport.

Assessment of Sports Concussion in Female Athletes: A Role for Neuroinformatics?

Over the past decade, the intricacies of sports-related concussions among female athletes have become readily apparent. Traditional clinical methods for diagnosing concussions suffer limitations when applied to female athletes, often failing to capture subtle changes in brain structure and function. Advanced neuroinformatics techniques and machine learning models have become invaluable assets in this endeavor. While these technologies have been extensively employed in understanding concussion in male athletes, there remains a significant gap in our comprehension of their effectiveness for female athletes. With its remarkable data analysis capacity, machine learning offers a promising avenue to bridge this deficit. By harnessing the power of machine learning, researchers can link observed phenotypic neuroimaging data to sex-specific biological mechanisms, unraveling the mysteries of concussions in female athletes. Furthermore, embedding methods within machine learning enable examining brain architecture and its alterations beyond the conventional anatomical reference frame. In turn, allows researchers to gain deeper insights into the dynamics of concussions, treatment responses, and recovery processes. This paper endeavors to address the crucial issue of sex differences in multimodal neuroimaging experimental design and machine learning approaches within female athlete populations, ultimately ensuring that they receive the tailored care they require when facing the challenges of concussions. Through better data integration, feature identification, knowledge representation, validation, etc., neuroinformaticists, are ideally suited to bring clarity, context, and explainabilty to the study of sports-related head injuries in males and in females, and helping to define recovery.

Sex differences in the extent of acute axonal pathologies after experimental concussion

Although human females appear be at a higher risk of concussion and suffer worse outcomes than males, underlying mechanisms remain unclear. With increasing recognition that damage to white matter axons is a key pathologic substrate of concussion, we used a clinically relevant swine model of concussion to explore potential sex differences in the extent of axonal pathologies. At 24 h post-injury, female swine displayed a greater number of swollen axonal profiles and more widespread loss of axonal sodium channels than males. Axon degeneration for both sexes appeared to be related to individual axon architecture, reflected by a selective loss of small caliber axons after concussion. However, female brains had a higher percentage of small caliber axons, leading to more extensive axon loss after injury compared to males. Accordingly, sexual dimorphism in axonal size is associated with more extensive axonal pathology in females after concussion, which may contribute to worse outcomes.

Associations of prior concussion severity with brain microstructure using mean apparent propagator magnetic resonance imaging

Magnetic resonance imaging (MRI) diffusion studies have shown chronic microstructural tissue abnormalities in athletes with history of concussion, but with inconsistent findings. Concussions with post-traumatic amnesia (PTA) and/or loss of consciousness (LOC) have been connected to greater physiological injury. The novel mean apparent propagator (MAP) MRI is expected to be more sensitive to such tissue injury than the conventional diffusion tensor imaging. This study examined effects of prior concussion severity on microstructure with MAP-MRI. Collegiate-aged athletes (N = 111, 38 females; ≥6 months since most recent concussion, if present) completed semistructured interviews to determine the presence of prior concussion and associated injury characteristics, including PTA and LOC. MAP-MRI metrics (mean non-Gaussian diffusion [NG Mean], return-to-origin probability [RTOP], and mean square displacement [MSD]) were calculated from multi-shell diffusion data, then evaluated for associations with concussion severity through group comparisons in a primary model (athletes with/without prior concussion) and two secondary models (athletes with/without prior concussion with PTA and/or LOC, and athletes with/without prior concussion with LOC only). Bayesian multilevel modeling estimated models in regions of interest (ROI) in white matter and subcortical gray matter, separately. In gray matter, the primary model showed decreased NG Mean and RTOP in the bilateral pallidum and decreased NG Mean in the left putamen with prior concussion. In white matter, lower NG Mean with prior concussion was present in all ROI across all models and was further decreased with LOC. However, only prior concussion with LOC was associated with decreased RTOP and increased MSD across ROI. Exploratory analyses conducted separately in male and female athletes indicate associations in the primary model may differ by sex. Results suggest microstructural measures in gray matter are associated with a general history of concussion, while a severity-dependent association of prior concussion may exist in white matter.

Selective head cooling in the acute phase of concussive injury: a neuroimaging study

Introduction

Neurovascular decoupling is a common consequence after brain injuries like sports-related concussion. Failure to appropriately match cerebral blood flow (CBF) with increases in metabolic demands of the brain can lead to alterations in neurological function and symptom presentation. Therapeutic hypothermia has been used in medicine for neuroprotection and has been shown to improve outcome. This study aimed to examine the real time effect of selective head cooling on healthy controls and concussed athletes via magnetic resonance spectroscopy (MRS) and arterial spin labeling (ASL) measures.

Methods

24 participants (12 controls; 12 concussed) underwent study procedures including the Post-Concussion Symptom Severity (PCSS) Rating Form and an MRI cooling protocol (pre-cooling (T1 MPRAGE, ASL, single volume spectroscopy (SVS)); during cooling (ASL, SVS)).

Results

Results showed general decreases in brain temperature as a function of time for both groups. Repeated measures ANOVA showed a significant main effect of time (F = 7.94, p < 0.001) and group (F = 22.21, p < 0.001) on temperature, but no significant interaction of group and time (F = 1.36, p = 0.237). CBF assessed via ASL was non-significantly lower in concussed individuals at pre-cooling and generalized linear mixed model analyses demonstrated a significant main effect of time for the occipital left ROI (F = 11.29, p = 0.002) and occipital right ROI (F = 13.39, p = 0.001). There was no relationship between any MRI metric and PCSS symptom burden.

Discussion

These findings suggest the feasibility of MRS thermometry to monitor alterations of brain temperature in concussed athletes and that metabolic responses in response to cooling after concussion may differ from controls.

Acute evaluation of sport-related concussion and implications for the Sport Concussion Assessment Tool (SCAT6) for adults, adolescents and children: a systematic review

OBJECTIVES

To systematically review the scientific literature regarding the acute assessment of sport-related concussion (SRC) and provide recommendations for improving the Sport Concussion Assessment Tool (SCAT6).

DATA SOURCES

Systematic searches of seven databases from 2001 to 2022 using key words and controlled vocabulary relevant to concussion, sports, SCAT, and acute evaluation.

ELIGIBILITY CRITERIA

(1) Original research articles, cohort studies, case-control studies, and case series with a sample of >10; (2) ≥80% SRC; and (3) studies using a screening tool/technology to assess SRC acutely (<7 days), and/or studies containing psychometric/normative data for common tools used to assess SRC.

DATA EXTRACTION

Separate reviews were conducted involving six subdomains: Cognition, Balance/Postural Stability, Oculomotor/Cervical/Vestibular, Emerging Technologies, and Neurological Examination/Autonomic Dysfunction. Paediatric/Child studies were included in each subdomain. Risk of Bias and study quality were rated by coauthors using a modified SIGN (Scottish Intercollegiate Guidelines Network) tool.

RESULTS

Out of 12 192 articles screened, 612 were included (189 normative data and 423 SRC assessment studies). Of these, 183 focused on cognition, 126 balance/postural stability, 76 oculomotor/cervical/vestibular, 142 emerging technologies, 13 neurological examination/autonomic dysfunction, and 23 paediatric/child SCAT. The SCAT discriminates between concussed and non-concussed athletes within 72 hours of injury with diminishing utility up to 7 days post injury. Ceiling effects were apparent on the 5-word list learning and concentration subtests. More challenging tests, including the 10-word list, were recommended. Test-retest data revealed limitations in temporal stability. Studies primarily originated in North America with scant data on children.

CONCLUSION

Support exists for using the SCAT within the acute phase of injury. Maximal utility occurs within the first 72 hours and then diminishes up to 7 days after injury. The SCAT has limited utility as a return to play tool beyond 7 days. Empirical data are limited in pre-adolescents, women, sport type, geographical and culturally diverse populations and para athletes.

PROSPERO REGISTRATION NUMBER

CRD42020154787.

Clinical recovery from concussion-return to school and sport: a systematic review and meta-analysis

OBJECTIVE

To define the time frames, measures used and modifying factors influencing recovery, return to school/learn (RTL) and return to sport (RTS) after sport-related concussion (SRC).

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

8 databases searched through 22 March 2022.

ELIGIBILITY CRITERIA

Studies with diagnosed/suspected SRC and interventions facilitating RTL/RTS or investigating the time and modifying factors for clinical recovery. Outcomes included days until symptom free, days until RTL and days until RTS. We documented study design, population, methodology and results. Risk of bias was evaluated using a modified Scottish Intercollegiate Guidelines Network tool.

RESULTS

278 studies were included (80.6% cohort studies and 92.8% from North America). 7.9% were considered high-quality studies, while 23.0% were considered high risk of bias and inadmissible. The mean days until symptom free was 14.0 days (95% CI: 12.7, 15.4; I²=98.0%). The mean days until RTL was 8.3 (95% CI: 5.6, 11.1; I²=99.3%), with 93% of athletes having a full RTL by 10 days without new academic support. The mean days until RTS was 19.8 days (95% CI: 18.8, 20.7; I²=99.3%), with high heterogeneity between studies. Several measures define and track recovery, with initial symptom burden remaining the strongest predictor of longer days until RTS. Continuing to play and delayed access to healthcare providers were associated with longer recovery. Premorbid and postmorbid factors (eg, depression/anxiety, migraine history) may modify recovery time frames. Though point estimates suggest that female sex or younger age cohorts take longer to recover, the heterogeneity of study designs, outcomes and overlap in CIs with male sex or older age cohorts suggests that all have similar recovery patterns.

CONCLUSION

Most athletes have full RTL by 10 days but take twice as long for an RTS.

PROSPERO REGISTRATION NUMBER

CRD42020159928.

Median Time to Return to Sports After Concussion Is Within 21 Days in 80% of Published Studies

PURPOSE

To perform a systematic review of the literature and evaluate the return to play (RTP) time frame after a concussion diagnosis. Our secondary purpose was to analyze and compare different prognostic variables affecting concussions, time to return to school, time to symptom resolution of concussive symptoms, and time each patient spent in the RTP protocol.

METHODS

A PubMed, Scopus, Medline, Embase, and Cochrane Library database literature review was performed in August 2022. The studies needed to report, in days, the length of time a patient/athlete was removed from play due to concussion management. The Risk of Bias in Non-Randomized Studies of Interventions tool was used for risk of bias for each study, and Methodological Index for Non-Randomized Studies criteria were used for quality assessment.

RESULTS

There were 65 studies included in the systematic review and a total of 21,966 patients evaluated. The RTP time intervals ranged from 1 to 1,820 days, with 80.7% of the median RTP time frames for each study within 21 days. Preconcussion risk factors for prolonged RTP included female sex, younger age, presence of psychiatric disorders, and history of previous concussion. Postconcussion risk factors included severe symptom scores at initial clinic visit, loss of consciousness, nonelite athletes, and delayed removal from competition. The most common sports resulting in concussion were contact sports, most commonly football and soccer. Median time to return to school was 3 to 23 days. Median time to symptom resolution ranged from 2 to 11 days. Median time in RTP protocol was 1 to 6 days.

CONCLUSIONS

Median time to return to sports after concussion is within 21 days in 80% of published studies.

LEVEL OF EVIDENCE

IV, systematic review of Level I to IV studies.

Altered connectivity of default mode and executive control networks among female patients with persistent post-concussion symptoms

OBJECTIVE

To examine the roles of the default mode network (DMN) and executive control network (ECN) in prolonged recovery after mild traumatic brain injury (mTBI), and relationships with indices of white matter microstructural injury.

METHODS

Seventeen mTBI patients with persistent symptoms were imaged an average of 21.5 months post-injury, along with 23 healthy controls. Resting-state functional magnetic resonance imaging (rs-fMRI) was used to evaluate functional connectivity (FC) of the DMN and ECN. Diffusion tensor imaging (DTI) quantified fractional anisotropy, along with mean, axial and radial diffusivity of white matter tracts.

RESULTS

Compared to controls, patients with mTBI had increased functional connectivity of the DMN and ECN to brain regions implicated in salience and frontoparietal networks, and increased white matter diffusivity within the cerebrum and brainstem. Among the patients, FC was correlated with better neurocognitive test scores, while diffusivity was correlated with more severe self-reported symptoms. The FC and diffusivity values within abnormal brain regions were not significantly correlated.

CONCLUSION

For female mTBI patients with prolonged symptoms, hyper-connectivity may represent a compensatory response that helps to mitigate the effects of mTBI on cognition. These effects are unrelated to indices of microstructural injury, which are correlated with symptom severity, suggesting that rs-fMRI and DTI may capture distinct aspects of pathophysiology.

Persistent white matter vulnerability in a mouse model of mild traumatic brain injury

Background

Following one mild traumatic brain injury (mTBI), there is a window of vulnerability during which subsequent mTBIs can cause substantially exacerbated impairments. Currently, there are no known methods to monitor, shorten or mitigate this window.

Methods

To characterize a preclinical model of this window of vulnerability, we first gave male and female mice one or two high-depth or low-depth mTBIs separated by 1, 7, or 14 days. We assessed brain white matter integrity using silver staining within the corpus callosum and optic tracts, as well as behavioural performance on the Y-maze test and visual cliff test.

Results

The injuries resulted in windows of white matter vulnerability longer than 2 weeks but produced no behavioural impairments. Notably, this window duration is substantially longer than those reported in any previous preclinical vulnerability study, despite our injury model likely being milder than the ones used in those studies. We also found that sex and impact depth differentially influenced white matter integrity in different white matter regions.

Conclusions

These results suggest that the experimental window of vulnerability following mTBI may be longer than previously reported. Additionally, this work highlights the value of including white matter damage, sex, and replicable injury models for the study of post-mTBI vulnerability and establishes important groundwork for the investigation of potential vulnerability mechanisms, biomarkers, and therapies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12868-022-00730-y.