Clinical, Biomarker, and Research Tests Among US Government Personnel and Their Family Members Involved in Anomalous Health Incidents.

Importance: Since 2015, US government and related personnel have reported dizziness, pain, visual problems, and cognitive dysfunction after experiencing intrusive sounds and head pressure. The US government has labeled these anomalous health incidents (AHIs). Objective: To assess whether participants with AHIs differ significantly from US government control participants with respect to clinical, research, and biomarker assessments. Design, Setting, and Participants: Exploratory study conducted between June 2018 and July 2022 at the National Institutes of Health Clinical Center, involving 86 US government staff and family members with AHIs from Cuba, Austria, China, and other locations as well as 30 US government control participants. Exposures: AHIs. Main Outcomes and Measures: Participants were assessed with extensive clinical, auditory, vestibular, balance, visual, neuropsychological, and blood biomarkers (glial fibrillary acidic protein and neurofilament light) testing. The patients were analyzed based on the risk characteristics of the AHI identifying concerning cases as well as geographic location. Results: Eighty-six participants with AHIs (42 women and 44 men; mean [SD] age, 42.1 [9.1] years) and 30 vocationally matched government control participants (11 women and 19 men; mean [SD] age, 43.8 [10.1] years) were included in the analyses. Participants with AHIs were evaluated a median of 76 days (IQR, 30-537) from the most recent incident. In general, there were no significant differences between participants with AHIs and control participants in most tests of auditory, vestibular, cognitive, or visual function as well as levels of the blood biomarkers. Participants with AHIs had significantly increased fatigue, depression, posttraumatic stress, imbalance, and neurobehavioral symptoms compared with the control participants. There were no differences in these findings based on the risk characteristics of the incident or geographic location of the AHIs. Twenty-four patients (28%) with AHI presented with functional neurological disorders. Conclusions and Relevance: In this exploratory study, there were no significant differences between individuals reporting AHIs and matched control participants with respect to most clinical, research, and biomarker measures, except for objective and self-reported measures of imbalance and symptoms of fatigue, posttraumatic stress, and depression. This study did not replicate the findings of previous studies, although differences in the populations included and the timing of assessments limit direct comparisons.

Neuroimaging Findings in US Government Personnel and Their Family Members Involved in Anomalous Health Incidents.

Importance: US government personnel stationed internationally have reported anomalous health incidents (AHIs), with some individuals experiencing persistent debilitating symptoms. Objective: To assess the potential presence of magnetic resonance imaging (MRI)-detectable brain lesions in participants with AHIs, with respect to a well-matched control group. Design, Setting, and Participants: This exploratory study was conducted at the National Institutes of Health (NIH) Clinical Center and the NIH MRI Research Facility between June 2018 and November 2022. Eighty-one participants with AHIs and 48 age- and sex-matched control participants, 29 of whom had similar employment as the AHI group, were assessed with clinical, volumetric, and functional MRI. A high-quality diffusion MRI scan and a second volumetric scan were also acquired during a different session. The structural MRI acquisition protocol was optimized to achieve high reproducibility. Forty-nine participants with AHIs had at least 1 additional imaging session approximately 6 to 12 months from the first visit. Exposure: AHIs. Main Outcomes and Measures: Group-level quantitative metrics obtained from multiple modalities: (1) volumetric measurement, voxel-wise and region of interest (ROI)-wise; (2) diffusion MRI-derived metrics, voxel-wise and ROI-wise; and (3) ROI-wise within-network resting-state functional connectivity using functional MRI. Exploratory data analyses used both standard, nonparametric tests and bayesian multilevel modeling. Results: Among the 81 participants with AHIs, the mean (SD) age was 42 (9) years and 49% were female; among the 48 control participants, the mean (SD) age was 43 (11) years and 42% were female. Imaging scans were performed as early as 14 days after experiencing AHIs with a median delay period of 80 (IQR, 36-544) days. After adjustment for multiple comparisons, no significant differences between participants with AHIs and control participants were found for any MRI modality. At an unadjusted threshold (P < .05), compared with control participants, participants with AHIs had lower intranetwork connectivity in the salience networks, a larger corpus callosum, and diffusion MRI differences in the corpus callosum, superior longitudinal fasciculus, cingulum, inferior cerebellar peduncle, and amygdala. The structural MRI measurements were highly reproducible (median coefficient of variation <1% across all global volumetric ROIs and <1.5% for all white matter ROIs for diffusion metrics). Even individuals with large differences from control participants exhibited stable longitudinal results (typically, <±1% across visits), suggesting the absence of evolving lesions. The relationships between the imaging and clinical variables were weak (median Spearman ρ = 0.10). The study did not replicate the results of a previously published investigation of AHIs. Conclusions and Relevance: In this exploratory neuroimaging study, there were no significant differences in imaging measures of brain structure or function between individuals reporting AHIs and matched control participants after adjustment for multiple comparisons.

Associations between white matter integrity and postural control in adults with traumatic brain injury.

Abnormalities of postural sway have been extensively reported in traumatic brain injury (TBI). However, the underlying neural correlates of balance disturbances in TBI remain to be elucidated. Studies in children with TBI have reported associations between the Sensory Organization Test (SOT) and measures of white matter (WM) integrity with diffusion tensor imaging (DTI) in brain areas responsible for multisensory integration. This study seeks to replicate those associations in adults as well as explore relationships between DTI and the Limits of Stability (LOS) Test. Fifty-six participants (43±17 years old) with a history of TBI were tested 30 days to 5 years post-TBI. This study confirmed results in children for associations between the SOT and the medial lemniscus as well as middle cerebellar peduncle, and revealed additional associations with the posterior thalamic radiation. Additionally, this study found significant correlations between abnormal LOS scores and impaired WM integrity in the cingulum, corpus callosum, corticopontine and corticospinal tracts, fronto-occipital fasciculi, longitudinal fasciculi, medial lemniscus, optic tracts and thalamic radiations. Our findings indicate the involvement of a broad range of WM tracts in the control of posture, and demonstrate the impact of TBI on balance via disruptions to WM integrity.

Headaches in Traumatic Brain Injury: Improvement Over Time, Associations With Quality of Life, and Impact of Migraine-Type Headaches.

OBJECTIVE: To describe headache characteristics over time in patients with traumatic brain injury (TBI). SETTING: Patients enrolled and followed at the National Institutes of Health Clinical Center between 2011 and 2020. PARTICIPANTS: There were 147 patients with TBI, with 74 mild TBI (mTBI), 49 moderate (modTBI), 24 severe (sTBI), and 20 individuals without brain injury (IWBIs). DESIGN: Regular surveys of headache characteristics in patients with TBI were conducted. Patients were enrolled as early as 30 days post-injury and followed up to 5 years, for 419 total visits and 80 patients with multiple return visits. MAIN MEASURES: Surveys of headache characteristics, including headache severity, were measured on a 0- to 10-point Likert scale and headache frequency quantified as headaches per month. Patients with migraine-type headaches ( n = 39) were identified by a clinician-administered tool. Functional outcomes were measured using the Glasgow Outcome Scale-Extended (GOS-E) and quality of life by the Satisfaction with Life Scale (SWLS) and the 36-item Short Form Survey (SF-36). RESULTS: At their initial visit, patients with TBI had more severe and frequent headaches than IWBIs (median 5 vs 2.5, P < .001; median 2 vs 0.2, P < .001), as did patients with mTBI compared with modTBI/sTBI (all P ≤ .01). Migraines were associated with lower SWLS and SF-36 scores. Migraines and young age were associated with higher headache severity and frequency across time points. Longitudinally, time post-injury correlated with improvement in headache severity and frequency without differences by injury severity. However, time post-injury did not correlate with improvement in headache characteristics in a patient subgroup with moderate/severe headaches. CONCLUSION: Our findings suggest that patients with mild, moderate, or severe TBI see improvement in headaches over time. However, patients should be counseled that improvement is modest and seen more in patients with milder headache symptoms. Patients with migraine headaches in particular are at risk for worse headache characteristics with greater impact on quality of life.

Association of Plasma Biomarker Levels With Their CSF Concentration and the Number and Severity of Concussions in Professional Athletes.

BACKGROUND AND OBJECTIVES: To examine whether the brain biomarkers total-tau (T-tau), glial fibrillary acidic protein (GFAP), and ß-amyloid (Aß) isomers 40 and 42 in plasma relate to the corresponding concentrations in CSF, blood-brain barrier integrity, and duration of postconcussion syndrome (PCS) due to repetitive head impacts (RHIs) in professional athletes. METHOD: In this cross-sectional study, professional athletes with persistent PCS due to RHI (median of 1.5 years after recent concussion) and uninjured controls were assessed with blood and CSF sampling. The diagnosis of PCS was based on the Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition). The athletes were enrolled through information flyers about the study sent to the Swedish Hockey League (SHL) and the SHL Medicine Committee. The controls were enrolled through flyers at University of Gothenburg and Sahlgrenska University Hospital, Sweden. The participants underwent lumbar puncture and blood assessment at Sahlgrenska University Hospital. The main outcome measures were history of RHI and PCS severity (PCS >1 year vs PCS <1 year) in relation to plasma and CSF concentrations of T-tau, GFAP, Aß40, and Aß42. Plasma T-tau, GFAP, Aß40, and Aß42 were quantified using an ultrasensitive assay technology. RESULTS: A total of 47 participants (28 athletes [median age 28 years, range 18-52] with persistent PCS due to RHI and 19 controls [median age, 25 years, range 21-35]) underwent paired blood and CSF sampling. T-tau, Aß40, and Aß42 concentrations measured in plasma did not correlate with the corresponding CSF concentrations, while there was a correlation between plasma and CSF levels of GFAP (r = 0.45, p = 0.020). There were no significant relationships between plasma T-tau, GFAP, and blood-brain barrier integrity as measured by the CSF:serum albumin ratio. T-tau, GFAP, Aß40, and Aß42 measured in plasma did not relate to PCS severity. None of the markers measured in plasma correlated with number of concussions, except decreased Aß42 in those with higher number of concussions (r = -0.40, p = 0.04). DISCUSSION: T-tau, GFAP, Aß40, and Aß42 measured in plasma do not correspond to CSF measures and may have limited utility for the evaluation of the late effects of RHI, compared with when measured in CSF. CLASSIFICATION OF EVIDENCE: This study provides Class III evidence that in professional athletes with postconcussion symptoms, plasma concentrations of T-tau, GFAP, Aß40, and Aß42 are not informative in the diagnosis of late effects of repetitive head injuries.

Advanced brain age in deployment-related traumatic brain injury: A LIMBIC-CENC neuroimaging study.

OBJECTIVE: To determine if history of mild traumatic brain injury (mTBI) is associated with advanced or accelerated brain aging among the United States (US) military Service Members and Veterans. METHODS: Eight hundred and twenty-two participants (mean age = 40.4 years, 714 male/108 female) underwent MRI sessions at eight sites across the US. Two hundred and one participants completed a follow-up scan between five months and four years later. Predicted brain ages were calculated using T1-weighted MRIs and then compared with chronological ages to generate an Age Deviation Score for cross-sectional analyses and an Interval Deviation Score for longitudinal analyses. Participants also completed a neuropsychological battery, including measures of both cognitive functioning and psychological health. RESULT: In cross-sectional analyses, males with a history of deployment-related mTBI showed advanced brain age compared to those without (t(884) = 2.1, p = .038), while this association was not significant in females. In follow-up analyses of the male participants, severity of posttraumatic stress disorder (PTSD), depression symptoms, and alcohol misuse were also associated with advanced brain age. CONCLUSION: History of deployment-related mTBI, severity of PTSD and depression symptoms, and alcohol misuse are associated with advanced brain aging in male US military Service Members and Veterans.

Sleep quality: A common thread linking depression, post-traumatic stress, and post-concussive symptoms to biomarkers of neurodegeneration following traumatic brain injury.

OBJECTIVE: Following mild traumatic brain injury (mTBI), many individuals suffer from persistent post-concussive, depressive, post-traumatic stress, and sleep-related symptoms. Findings from self-report scales link these symptoms to biomarkers of neurodegeneration, although the underlying pathophysiology is unclear. Each linked self-report scale includes sleep items, raising the possibility that despite varied symptomology, disordered sleep may underlie these associations. To isolate sleep effects, we examined associations between post-mTBI biomarkers of neurodegeneration and symptom scales according to composite, non-sleep, and sleep components. METHODS: Plasma biomarkers and self-report scales were obtained from 143 mTBI-positive warfighters. Pearson's correlations and regression models were constructed to estimate associations between total, sleep, and non-sleep scale items with biomarker levels, and with measured sleep quality. RESULTS: Symptom severity positively correlated with biomarker levels across scales. Biomarker associations were largely unchanged when sleep items were included, excluded, or considered in isolation. Pittsburgh Sleep Quality Index demonstrated strong correlations with sleep and non-sleep items of all scales. CONCLUSION: The congruency of associations raises the possibility of a common pathophysiological process underlying differing symptomologies. Given its role in neurodegeneration and mood dysregulation, sleep physiology seems a likely candidate. Future longitudinal studies should test this hypothesis, with a focus on identifying novel sleep-related therapeutic targets.

Neurochemical Markers of Traumatic Brain Injury: Relevance to Acute Diagnostics, Disease Monitoring, and Neuropsychiatric Outcome Prediction.

Considerable advancements have been made in the quantification of biofluid-based biomarkers for traumatic brain injury (TBI), which provide a clinically accessible window to investigate disease mechanisms and progression. Methods with improved analytical sensitivity compared with standard immunoassays are increasingly used, and blood tests are being used in the diagnosis, monitoring, and outcome prediction of TBI. Most work to date has focused on acute TBI diagnostics, while the literature on biomarkers for long-term sequelae is relatively scarce. In this review, we give an update on the latest developments in biofluid-based biomarker research in TBI and discuss how acute and prolonged biomarker changes can be used to detect and quantify brain injury and predict clinical outcome and neuropsychiatric sequelae.

Arterial Spin Labeling Reveals Elevated Cerebral Blood Flow with Distinct Clusters of Hypo- and Hyperperfusion after Traumatic Brain Injury.

Imaging detection of brain perfusion alterations after traumatic brain injury (TBI) may provide prognostic insights. In this study, we used arterial spin labeling (ASL) to quantify cross-sectional and longitudinal changes in cerebral blood flow (CBF) after TBI and correlated changes with clinical outcome. We analyzed magnetic resonance imaging scans from adult participants with TBI requiring hospitalization in the acute (2 weeks post-injury, n = 33) and chronic (6 months post-injury, n = 16) phases, with 13 participants scanned longitudinally at both time points. We also analyzed 18 age- and sex-matched healthy controls. Whole-brain CBF maps were derived using a three-dimensional pseudo-continuous arterial spin label technique. Mean CBF across tissue-based regions (whole brain, gray matter, and white matter) was compared cross-sectionally and longitudinally. In addition, individual-level clusters of abnormal perfusion were identified using voxel-based z-score analysis of relative CBF maps, and number and volume of abnormally hypo- and hyperperfused clusters were assessed cross-sectionally and longitudinally. Finally, all CBF measures were correlated with clinical outcome measures. Mean global and gray matter CBF were significantly elevated in acute and chronic TBI participants compared to controls. Participants with better outcome at 6 months post-injury tended to have higher CBF in the acute phase compared to those with poorer outcome. Acute TBI participants had a significantly greater volume of hypo- and hyperperfused brain tissue compared to controls, with these regions partially normalizing by the chronic phase. Our findings demonstrate global elevation of CBF with focal hypo- and hyperperfusion in the early post-injury period and suggest a reparative role for acute elevation in CBF post-TBI.

Extracellular vesicle concentrations of glial fibrillary acidic protein and neurofilament light measured 1 year after traumatic brain injury.

Traumatic brain injury (TBI) is linked to long-term symptoms in a sub-set of patients who sustain an injury, but this risk is not universal, leading us and others to question the nature of individual variability in recovery trajectories. Extracellular vesicles (EVs) are a promising, novel avenue to identify blood-based biomarkers for TBI. Here, our aim was to determine if glial fibrillary acidic protein (GFAP) and neurofilament light (NfL) measured 1-year postinjury in EVs could distinguish patients from controls, and whether these biomarkers relate to TBI severity or recovery outcomes. EV GFAP and EV NfL were measured using an ultrasensitive assay in 72 TBI patients and 20 controls. EV GFAP concentrations were elevated in moderate and severe TBI compared to controls (p's < 0.001) and could distinguish controls from moderate (AUC = 0.86) or severe TBI (AUC = 0.88). Increased EV GFAP and EV NfL levels were associated with lower 1-year Glasgow Outcome Scale-Extended (GOS-E) score (p's < 0.05). These findings suggest that blood-derived EV concentrations of GFAP and NfL drawn even 1 year after injury are higher in TBI patients compared to controls, and are related to injury severity and poor recovery outcomes, suggesting that TBIs alter the activity of these biomarkers, likely contributing to individual variability in recovery.

Brain and blood biomarkers of tauopathy and neuronal injury in humans and rats with neurobehavioral syndromes following blast exposure.

Traumatic brain injury (TBI) is a risk factor for the later development of neurodegenerative diseases that may have various underlying pathologies. Chronic traumatic encephalopathy (CTE) in particular is associated with repetitive mild TBI (mTBI) and is characterized pathologically by aggregation of hyperphosphorylated tau into neurofibrillary tangles (NFTs). CTE may be suspected when behavior, cognition, and/or memory deteriorate following repetitive mTBI. Exposure to blast overpressure from improvised explosive devices (IEDs) has been implicated as a potential antecedent for CTE amongst Iraq and Afghanistan Warfighters. In this study, we identified biomarker signatures in rats exposed to repetitive low-level blast that develop chronic anxiety-related traits and in human veterans exposed to IED blasts in theater with behavioral, cognitive, and/or memory complaints. Rats exposed to repetitive low-level blasts accumulated abnormal hyperphosphorylated tau in neuronal perikarya and perivascular astroglial processes. Using positron emission tomography (PET) and the [18F]AV1451 (flortaucipir) tau ligand, we found that five of 10 veterans exhibited excessive retention of [18F]AV1451 at the white/gray matter junction in frontal, parietal, and temporal brain regions, a typical localization of CTE tauopathy. We also observed elevated levels of neurofilament light (NfL) chain protein in the plasma of veterans displaying excess [18F]AV1451 retention. These findings suggest an association linking blast injury, tauopathy, and neuronal injury. Further study is required to determine whether clinical, neuroimaging, and/or fluid biomarker signatures can improve the diagnosis of long-term neuropsychiatric sequelae of mTBI.

Poor sleep correlates with biomarkers of neurodegeneration in mild traumatic brain injury patients: a CENC study.

STUDY OBJECTIVES: Sleep disorders affect over half of mild traumatic brain injury (mTBI) patients. Despite evidence linking sleep and neurodegeneration, longitudinal TBI-related dementia studies have not considered sleep. We hypothesized that poor sleepers with mTBI would have elevated markers of neurodegeneration and lower cognitive function compared to mTBI good sleepers and controls. Our objective was to compare biomarkers of neurodegeneration and cognitive function with sleep quality in warfighters with chronic mTBI. METHODS: In an observational warfighters cohort (n = 138 mTBI, 44 controls), the Pittsburgh Sleep Quality Index (PSQI) was compared with plasma biomarkers of neurodegeneration and cognitive scores collected an average of 8 years after injury. RESULTS: In the mTBI cohort, poor sleepers (PSQI ≥ 10, n = 86) had elevated plasma neurofilament light (NfL, x̅ = 11.86 vs 7.91 pg/mL, p = 0.0007, d = 0.63) and lower executive function scores by the categorical fluency (x̅ = 18.0 vs 21.0, p = 0.0005, d = -0.65) and stop-go tests (x̅ = 30.1 vs 31.1, p = 0.024, d = -0.37). These findings were not observed in controls (n = 44). PSQI predicted NfL (beta = 0.22, p = 0.00002) and tau (beta = 0.14, p = 0.007), but not amyloid ß42. Poor sleepers showed higher obstructive sleep apnea (OSA) risk by STOP-BANG scores (x̅ = 3.8 vs 2.7, p = 0.0005), raising the possibility that the PSQI might be partly secondary to OSA. CONCLUSIONS: Poor sleep is linked to neurodegeneration and select measures of executive function in mTBI patients. This supports implementation of validated sleep measures in longitudinal studies investigating pathobiological mechanisms of TBI related neurodegeneration, which could have therapeutic implications.

Serum-neuroproteins, near-infrared spectroscopy, and cognitive outcome after beach-chair shoulder surgery: Observational cohort study analyses.

BACKGROUND: Cerebral hypoxia may occur during surgery but currently used cerebral oxygenation saturation (rSO2) monitors remain controversial with respect to improving clinical outcome. Novel neuroprotein biomarkers are potentially released into systemic circulation and combined with near-infrared spectroscopy (NIRS) could clarify the presence of per-operative cerebral hypoxia. We investigated changes to serum-neuroprotein concentrations post-surgically, paired with NIRS and cognitive outcome, in patients operated in the beach chair position (BCP). METHODS: A prospective cohort in 28 shoulder surgery patients placed in the BCP. Blood samples were collected before induction of anaesthesia, and 2 hours and 3-5 days post-operatively. We analysed blood levels of biomarkers including tau and neurofilament light (NFL). We post hoc assessed the cross-wise relationship between biomarker levels and post-surgical changes in cognitive function and intraoperatively monitored rSO2 from NIRS. RESULTS: Serum-NFL decreased from 24.2 pg/mL to 21.5 (P = .02) 2 hours post-operatively, then increased to 27.7 pg/mL on day 3-5 (P = .03). Conversely, s-tau increased from 0.77 pg/mL to 0.98 (2 h), then decreased to 0.81 on day 3-5 (P = .08). In 14/28 patients, episodic rSO2 below 55% occurred, and the duration < 55% was correlated to change in s-tau (P < .05). The cognitive function z-score at 1 week and 3 mo. correlated to the change in tau (P = .01), but not to NFL. CONCLUSION: Some biomarkers were significantly changed with surgery in the beach chair position. The change was at some points associated to post-operative cognitive decline, and to intraoperative low rSO2. (237).

Quality of life of ice hockey players after retirement due to concussions.

BACKGROUND: Sports-related concussion (SRC) is increasingly recognized as a potential health problem in ice hockey. Quality of life (QoL) in players retiring due to SRC has not been thoroughly addressed. MATERIALS & METHODS: QoL using the Sports Concussion Assessment Tool 5th Edition, Impact of Event Scale-Revised and Short Form Health Survey was measured in Swedish ice hockey players who retired due to persistence of postconcussion symptoms or fear of attaining additional SRC. RESULTS: A total of 76 players were assessed, on average of 5 years after their most recent SRC. Overall, retired players had a high burden of postconcussion symptoms and reduced QoL. CONCLUSION: Retired concussed ice hockey players have a reduced QoL, particularly those retiring due to postconcussion symptoms. Symptom burden should be continuously evaluated and guide the decision to retire.

Fluid Biomarkers for Chronic Traumatic Encephalopathy.

Chronic traumatic encephalopathy (CTE) is a neuropathological condition that has been described in individuals who have been exposed to repetitive head impacts, including concussions and subconcussive trauma. Currently, there is no fluid or imaging biomarker for diagnosing CTE during life. Based on retrospective clinical data, symptoms of CTE include changes in behavior, cognition, and mood, and may develop after a latency phase following the injuries. However, these symptoms are often nonspecific, making differential diagnosis based solely on clinical symptoms unreliable. Thus, objective biomarkers for CTE pathophysiology would be helpful in understanding the course of the disease as well as in the development of preventive and therapeutic measures. Herein, we review the literature regarding fluid biomarkers for repetitive concussive and subconcussive head trauma, postconcussive syndrome, as well as potential candidate biomarkers for CTE. We also discuss technical challenges with regard to the current fluid biomarkers and potential pathways to advance the most promising biomarker candidates into clinical routine.

Time course and diagnostic utility of NfL, tau, GFAP, and UCH-L1 in subacute and chronic TBI.

OBJECTIVE: To determine whether neurofilament light (NfL), glial fibrillary acidic protein (GFAP), tau, and ubiquitin C-terminal hydrolase-L1 (UCH-L1) measured in serum relate to traumatic brain injury (TBI) diagnosis, injury severity, brain volume, and diffusion tensor imaging (DTI) measures of traumatic axonal injury (TAI) in patients with TBI. METHODS: Patients with TBI (n = 162) and controls (n = 68) were prospectively enrolled between 2011 and 2019. Patients with TBI also underwent serum, functional outcome, and imaging assessments at 30 (n = 30), 90 (n = 48), and 180 (n = 59) days, and 1 (n = 84), 2 (n = 57), 3 (n = 46), 4 (n = 38), and 5 (n = 29) years after injury. RESULTS: At enrollment, patients with TBI had increased serum NfL compared to controls (p < 0.0001). Serum NfL decreased over the course of 5 years but remained significantly elevated compared to controls. Serum NfL at 30 days distinguished patients with mild, moderate, and severe TBI from controls with an area under the receiver-operating characteristic curve (AUROC) of 0.84, 0.92, and 0.92, respectively. At enrollment, serum GFAP was elevated in patients with TBI compared to controls (p < 0.001). GFAP showed a biphasic release in serum, with levels decreasing during the first 6 months of injury but increasing over the subsequent study visits. The highest AUROC for GFAP was measured at 30 days, distinguishing patients with moderate and severe TBI from controls (both 0.89). Serum tau and UCH-L1 showed weak associations with TBI severity and neuroimaging measures. Longitudinally, serum NfL was the only biomarker that was associated with the likely rate of MRI brain atrophy and DTI measures of progression of TAI. CONCLUSIONS: Serum NfL shows greater diagnostic and prognostic utility than GFAP, tau, and UCH-L1 for subacute and chronic TBI. CLASSIFICATION OF EVIDENCE: This study provides Class III evidence that serum NfL distinguishes patients with mild TBI from healthy controls.

Neurofilament light as a biomarker in traumatic brain injury.

OBJECTIVE: To determine whether serum neurofilament light (NfL) correlates with CSF NfL, traumatic brain injury (TBI) diagnosis, injury severity, brain volume, and diffusion tensor imaging (DTI) estimates of traumatic axonal injury (TAI). METHODS: Participants were prospectively enrolled in Sweden and the United States between 2011 and 2019. The Swedish cohort included 45 hockey players with acute concussion sampled at 6 days, 31 with repetitive concussion with persistent postconcussive symptoms (PCS) assessed with paired CSF and serum (median 1.3 years after concussion), 28 preseason controls, and 14 nonathletic controls. Our second cohort included 230 clinic-based participants (162 with TBI and 68 controls). Patients with TBI also underwent serum, functional outcome, and imaging assessments at 30 (n = 30), 90 (n = 48), and 180 (n = 59) days and 1 (n = 84), 2 (n = 57), 3 (n = 46), 4 (n = 38), and 5 (n = 29) years after injury. RESULTS: In athletes with paired specimens, CSF NfL and serum NfL were correlated (r = 0.71, p < 0.0001). CSF and serum NfL distinguished players with PCS >1 year from PCS ≤1 year (area under the receiver operating characteristic curve [AUROC] 0.81 and 0.80). The AUROC for PCS >1 year vs preseason controls was 0.97. In the clinic-based cohort, NfL at enrollment distinguished patients with mild from those with moderate and severe TBI (p < 0.001 and p = 0.048). Serum NfL decreased over the course of 5 years (ß = -0.09 log pg/mL, p < 0.0001) but remained significantly elevated compared to controls. Serum NfL correlated with measures of functional outcome, MRI brain atrophy, and DTI estimates of TAI. CONCLUSIONS: Serum NfL shows promise as a biomarker for acute and repetitive sports-related concussion and patients with subacute and chronic TBI. CLASSIFICATION OF EVIDENCE: This study provides Class III evidence that increased concentrations of NfL distinguish patients with TBI from controls.

Losing the identity of a hockey player: the long-term effects of concussions.

AIM: To describe what suffering multiple concussions meant for former semi-professional or professional hockey players who were forced to end their career. RESULTS: Nine former Swedish hockey players, who once played on national or professional teams were interviewed. The interviews were analyzed with reference to hermeneutic phenomenology to interpret and explain their experiences. The theme of losing one's identity as a hockey player was constructed from five subthemes: being limited in everyday life, returning to the hockey stadium as soon as possible, forming a post career identity, lacking understanding and support, and preventing injuries by respecting other players. CONCLUSION: The former hockey players struggled with developing their off-the-ice identities and with finding other sources of meaning for their lives.