Repetitive mild traumatic brain injury in military veterans is associated with increased neuropsychological intra-individual variability

Lifetime Traumatic Brain Injury and Risk of Post-Concussive Symptoms in the Millennium Cohort Study

Traumatic brain injury (TBI) is prevalent among active duty military service members, with studies reporting up to 23% experiencing at least one TBI, with 10-60% of service members reporting at least one subsequent repeat TBI. A TBI has been associated with an increased risk of cumulative effects and long-term neurobehavioral symptoms, impacting operational readiness in the short-term and overall health in the long term. The association between multiple TBI and post-concussive symptoms (PCS), however, defined as symptoms that follow a concussion or TBI, in the military has not been adequately examined. Previous studies in military populations are limited by methodological issues including small sample sizes, the use of non-probability sampling, or failure to include the total number of TBI. To overcome these limitations, we examined the association between the total lifetime number of TBI and total number of PCS among U.S. active duty military service members who participated in the Millennium Cohort Study. A secondary data analysis was conducted using the Millennium Cohort Study's 2014 survey (n = 28,263) responses on self-reported TBI and PCS (e.g., fatigue, restlessness, sleep disturbances, poor concentration, or memory loss). Zero-inflated negative binomial models calculated prevalence ratios (PRs) and 95% confidence intervals (CIs) for the unadjusted and adjusted associations between lifetime TBIs and PCS. A third of military participants reported experiencing one or more TBIs during their lifetime with 72% reporting at least one PCS. As the mean number of PCS increased, mean lifetime TBIs increased. The mean number of PCS by those with four or more TBI (4.63) was more than twice that of those with no lifetime TBI (2.28). One, two, three, and four or more TBI had 1.10 (95% CI: 1.06-1.15), 1.19 (95% CI: 1.14-1.25), 1.23 (95% CI: 1.17-1.30), and 1.30 times (95% CI: 1.24-1.37) higher prevalence of PCS, respectively. The prevalence of PCS was 2.4 (95% CI: 2.32-2.48) times higher in those with post-traumatic stress disorder than their counterparts. Active duty military service members with a history of TBI are more likely to have PCS than those with no history of TBI. These results suggest an elevated prevalence of PCS as the number of TBI increased. This highlights the need for robust, longitudinal studies that can establish a temporal relationship between repetitive TBI and incidence of PCS. These findings have practical relevance for designing both workplace safety prevention measures and treatment options regarding the effect on and from TBI among military personnel.

Development and Validity of Norms for Cognitive Dispersion on the Uniform Data Set 3.0 Neuropsychological Battery

OBJECTIVE

Cognitive dispersion indexes intraindividual variability in performance across a battery of neuropsychological tests. Measures of dispersion show promise as markers of cognitive dyscontrol and everyday functioning difficulties; however, they have limited practical applicability due to a lack of normative data. This study aimed to develop and evaluate normed scores for cognitive dispersion among older adults.

METHOD

We analyzed data from 4,283 cognitively normal participants aged ≥50 years from the Uniform Data Set (UDS) 3.0. We describe methods for calculating intraindividual standard deviation (ISD) and coefficient of variation (CoV), as well as associated unadjusted scaled scores and demographically adjusted z-scores. We also examined the ability of ISD and CoV scores to differentiate between cognitively normal individuals (n = 4,283) and those with cognitive impairment due to Lewy body disease (n = 282).

RESULTS

We generated normative tables to map raw ISD and CoV scores onto a normal distribution of scaled scores. Cognitive dispersion indices were associated with age, education, and race/ethnicity but not sex. Regression equations were used to develop a freely accessible Excel calculator for deriving demographically adjusted normed scores for ISD and CoV. All measures of dispersion demonstrated excellent diagnostic utility when evaluated by the area under the curve produced from receiver operating characteristic curves.

CONCLUSIONS

Results of this study provide evidence for the clinical utility of sample-based and demographically adjusted normative standards for cognitive dispersion on the UDS 3.0. These standards can be used to guide interpretation of intraindividual variability among older adults in clinical and research settings.

Affective Disturbance and Neurocognitive Variability in College Athletes

OBJECTIVE

Research on the neurocognitive effects of comorbid mood/anxiety disturbance in college athletes is limited. Previous research found that athletes with comorbid depression/anxiety performed worse on measures of attention/processing speed (A/PS) at baseline compared to healthy controls. However, this work solely examined mean performance. The current study expands upon this work by examining intraindividual variability (IIV) in relation to affective disturbance.

METHOD

835 (M = 624, F = 211) collegiate athletes completed baseline neuropsychological testing. Athletes were separated into four groups (Healthy Mood [n = 582], Depression Alone [n = 137], Anxiety Alone [n = 54], and Co-Occurring Depression/Anxiety [n = 62]) based on self-reported anxiety and depression. IIV was examined globally and within composites of A/PS and memory via intraindividual standard deviation, with higher scores indicating greater variability.

RESULTS

Linear regression results revealed that the Co-Occurring Depression/Anxiety group exhibited greater variability within the memory composite compared to the Healthy Mood group, as well as the Depression Alone and Anxiety Alone groups. The Depression Alone and Anxiety Alone groups did not differ from the Healthy Mood group on memory IIV. None of the groups differed on A/PS or global IIV.

CONCLUSIONS

Athletes with co-occurring depression/anxiety demonstrated greater variability in performance on memory tasks. Greater dispersion is predictive of greater cognitive decline following concussion; therefore, it is important that neuropsychological performance is interpreted beyond measures of central tendency. These findings also highlight the importance of having baseline data available for athletes with affective disturbance, as these factors may influence performance, place athlete at risk for poorer outcomes, and skew future post-concussion comparisons.

Subjective memory complaints are associated with decreased cortical thickness in Veterans with histories of mild traumatic brain injury

Objective: Memory problems are frequently endorsed in Veterans following mild traumatic brain injury (mTBI), but subjective complaints are poorly associated with objective memory performance. Few studies have examined associations between subjective memory complaints and brain morphometry. We investigated whether self-reported memory problems were associated with objective memory performance and cortical thickness in Veterans with a history of mTBI. Methods: 40 Veterans with a history of remote mTBI and 29 Veterans with no history of TBI completed the Prospective-Retrospective Memory Questionnaire (PRMQ), PTSD Checklist (PCL), California Verbal Learning Test-2nd edition (CVLT-II), and 3 T T1 structural magnetic resonance imaging. Cortical thickness was estimated in 14 a priori frontal and temporal regions. Multiple regressions adjusting for age and PCL scores examined associations between PRMQ, CVLT-II scores, and cortical thickness within each Veteran group. Results: Greater subjective memory complaints on the PRMQ were associated with lower cortical thickness in the right middle temporal gyrus (β = 0.64, q = .004), right inferior temporal gyrus (β = 0.56, q = .014), right rostral middle frontal gyrus (β = 0.45, q = .046), and right rostral anterior cingulate gyrus (β = 0.58, q = .014) in the mTBI group but not the control group (q's > .05). These associations remained significant after adjusting for CVLT-II learning. CVLT-II performance was not associated with PRMQ score or cortical thickness in either group. Conclusions: Subjective memory complaints were associated with lower cortical thickness in right frontal and temporal regions, but not with objective memory performance, in Veterans with histories of mTBI. Subjective complaints post-mTBI may indicate underlying brain morphometry independently of objective cognitive testing.

Cognitive intra-individual variability in breast cancer survivors: A systematic review

Subjective and objective cognitive impairments in Breast Cancer Survivors (BCS) often do not correlate. One important contribution to the reported disparities may be the reliance on mean-based cognitive performance. Cognitive intra-individual variability (IIV) may provide important insights into these reported disparities. Cognitive IIV refers to the fluctuation in performance for an individual on either one cognitive task across a trial or dispersed across tasks within a neuropsychological test battery. The purpose of this systematic review was to search for and examine the literature on cognitive IIV in BCS. The PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) approach was used to search for all articles related to cognitive IIV in BCS. MEDLINE (via PubMed), Embase, and Scopus databases were searched using detailed search terms and strategies. Initially, 164 articles were retrieved but only 4 articles met the criteria for this systematic review. BCS differed from healthy controls in similar ways across the four studies, generally demonstrating similar performance but showing increased cognitive IIV for the more difficult tasks. Differences were enhanced later during chemotherapy. The four studies provide support for cognitive IIV as a useful measure to detect the subtle objective cognitive change often reported by BCS but frequently not detected by standard normed-based cognitive testing. Unexpectedly, measures of cognitive IIV were not consistently associated with self-reported measures of cognition.

A Projectile Concussive Impact Model Produces Neuroinflammation in Both Mild and Moderate-Severe Traumatic Brain Injury

Traumatic brain injury (TBI) is a major cause of death and disability and is experienced by nearly 3 million people annually as a result of falls, vehicular accidents, or from being struck by or against an object. While TBIs can range in severity, the majority of injuries are considered to be mild. However, TBI of any severity has the potential to have long-lasting neurological effects, including headaches, cognitive/memory impairments, mood dysfunction, and fatigue as a result of neural damage and neuroinflammation. Here, we modified a projectile concussive impact (PCI) model of TBI to deliver a closed-head impact with variable severity dependent on the material of the ball-bearing projectile. Adult male Sprague Dawley rats were evaluated for neurobehavioral, neuroinflammatory, and neural damage endpoints both acutely and longer-term (up to 72 h) post-TBI following impact with either an aluminum or stainless-steel projectile. Animals that received TBI using the stainless-steel projectile exhibited outcomes strongly correlated to moderate-severe TBI, such as prolonged unconsciousness, impaired neurobehavior, increased risk for hematoma and death, as well as significant neuronal degeneration and neuroinflammation throughout the cortex, hippocampus, thalamus, and cerebellum. In contrast, rats that received TBI with the aluminum projectile exhibited characteristics more congruous with mild TBI, such as a trend for longer periods of unconsciousness in the absence of neurobehavioral deficits, a lack of neurodegeneration, and mild neuroinflammation. Moreover, alignment of cytokine mRNA expression from the cortex of these rats with a computational model of neuron-glia interaction found that the moderate-severe TBI produced by the stainless-steel projectile strongly associated with the neuroinflammatory state, while the mild TBI existed in a state between normal and inflammatory neuron-glia interactions. Thus, these modified PCI protocols are capable of producing TBIs that model the clinical and experimental manifestations associated with both moderate-severe and mild TBI producing relevant models for the evaluation of the potential underlying roles of neuroinflammation and other chronic pathophysiology in the long-term outcomes associated with TBI.

Relationship between subjective report and objective assessment of neurocognitive functioning in persons with multiple sclerosis

OBJECTIVE

Persons with multiple sclerosis (PwMS) are at increased risk for cognitive dysfunction. Considering the impact and potential ramifications of cognitive dysfunction, it is important that cognition is routinely assessed in PwMS. Thus, it is also important to identify a screener that is accurate and sensitive to MS-related cognitive difficulties, which can inform decisions for more resource-intensive neuropsychological testing. However, research focused on available self-report screeners has been mixed, such as with the Multiple Sclerosis Neuropsychological Screening Questionnaire (MSNQ). This study aims to clarify the relationship between subjective and objective assessment of cognitive functioning in MS by examining domain-specific performance and intraindividual variability (IIV).

METHODS

87 PwMS (F = 65, M = 22) completed a comprehensive neuropsychological battery which included self- and informant-report measures of neurocognitive functioning. Scores were examined in relation to mean performance on five domains of cognitive functioning and two measures of IIV.

RESULTS

The MSNQ-Self was inversely associated with executive function, verbal memory, and visual memory; it was not associated with IIV. The MSNQ-Informant was inversely associated with executive function and verbal memory, and positively associated with one measure of IIV. The MSNQ-Self showed a correlation of moderate effect size with depression (r = .39) while the MSNQ-Informant did not.

CONCLUSIONS

Results suggest that the MSNQ-Self and MSNQ-Informant show similar utility. Our findings also suggest that domains of executive function and memory may be most salient, thus more reflected in subjective reports of cognitive functioning. Future work should further examine the impact of mood disturbance with cognitive performance and IIV.

Independent and Synergistic Associations Between TBI Characteristics and PTSD Symptom Clusters on Cognitive Performance and Postconcussive Symptoms in Iraq and Afghanistan Veterans

OBJECTIVE

The investigators sought to evaluate the independent and interactive associations between mild traumatic brain injury (mTBI) characteristics and posttraumatic stress disorder (PTSD) symptoms with regard to postconcussive symptoms and cognition among treatment-seeking veterans of the U.S. conflicts in Iraq and Afghanistan.

METHODS

Sixty-seven Iraq and Afghanistan veterans who had a history of mTBI and comorbid PTSD were grouped based on injury mechanism (blast versus nonblast) and number of lifetime mTBIs (one to two versus three or more). Independent associations between mTBI characteristics and PTSD symptom clusters were evaluated with regard to cognition and postconcussive symptoms. Follow-up analyses were conducted to determine any interactive associations between TBI characteristics and PTSD symptom clusters.

RESULTS

Higher PTSD symptoms, particularly hyperarousal, were associated with poorer executive functioning and higher postconcussive symptoms. No direct relationships were observed between PTSD symptom clusters and memory or processing speed. The relationship between hyperarousal and processing speed was moderated by lifetime mTBIs, such that those with a history of at least three mTBIs demonstrated a negative association between hyperarousal and processing speed. Blast-related mTBI history was associated with reduced processing speed, compared with non-blast-related mTBI. However, an interaction was observed such that among those with blast-related mTBI history, higher re-experiencing symptoms were associated with poorer processing speed, whereas veterans without history of blast-related mTBI did not demonstrate an association between processing speed and re-experiencing symptoms.

CONCLUSIONS

Higher hyperarousal and re-experiencing symptoms were associated with reduced processing speed among veterans with repetitive and blast-related mTBI history, respectively. PTSD symptoms, specifically hyperarousal, were associated with poorer executive functioning and higher postconcussive symptoms. Limited associations were found between injury characteristics and cognition chronically following mTBI. However, these results support synergistic effects of specific PTSD symptom clusters and TBI characteristics.

Elevated Neuropsychological Intraindividual Variability Predicts Poorer Health-Related Quality of Life in Veterans with a History of Mild Traumatic Brain Injury

We examined the association between cognitive functioning and health-related quality of life (HR-QOL) in military veterans with a history of mild traumatic brain injury (mTBI) using two methods to assess cognition: mean performance on cognitive composite scores and across-test intraindividual variability (IIV). The sample included 73 veterans (84.9% male; age, mean = 32.47 years) who completed neuropsychological testing and self-report questionnaires ∼7 years post-injury. Three cognitive composite scores representing mean performance were computed, including memory, attention/processing speed (A/PS), and executive functioning (EF). Three IIV indices were also calculated reflecting degree of dispersion across the same cognitive domains: memory-IIV, A/PS-IIV, and EF-IIV. The Posttraumatic Stress Disorder (PTSD) Checklist-Military Version (PCL-M) was used to assess current PTSD symptoms, and the World Health Organization Quality of Life Short Version Physical Health domain was used to assess HR-QOL. Hierarchical linear regressions adjusting for PTSD symptoms demonstrated that IIV indices, but not mean cognitive composite scores, significantly predicted HR-QOL. Specifically, memory-IIV, A/PS-IIV, and EF-IIV, when taken together, made an independent and significant contribution to the prediction of HR-QOL. Examination of the standardized coefficients showed that the A/PS-IIV index was uniquely associated with HR-QOL, such that higher A/PS-IIV scores significantly predicted poorer HR-QOL. Our results are the first to show that, in veterans with remote mTBI histories, greater fluctuations in cognitive performance significantly contribute to poorer HR-QOL, even after accounting for PTSD symptom severity. Moreover, findings suggest that, compared to traditional mean cognitive performance scores, measures of IIV may represent more sensitive indicators of clinical outcome and better align with subjective experiences of distress.

Unemployment Status Is Associated With Greater Cognitive Intraindividual Variability in Veterans With a History of Remote Mild TBI

OBJECTIVE

To examine the association between employment status and neuropsychological functioning in veterans with a history of remote mild traumatic brain injury (mTBI) using 2 approaches to assess cognitive performance: (a) standard, traditional mean cognitive performance; and (b) across-test intraindividual variability (IIV).

SETTING

Outpatient Veterans Affairs (VA) hospital.

PARTICIPANTS

Eligibility criteria included veterans with a history of mTBI who performed adequately on performance validity tests. Participants (N = 75; 37 employed, 38 unemployed) were evaluated, on average, about 5.5 years after their most recent mTBI.

DESIGN

Observational cohort study; all participants completed a clinical interview and a comprehensive neuropsychological assessment.

MAIN MEASURES

Primary outcomes of interest included mean cognitive composite test scores and IIV scores on tasks of memory, attention/processing speed, and executive functioning.

RESULTS

Logistic regression models showed that mean cognitive performance was not predictive of employment status; however, IIV indices were ( = 7.88, P = .048) and accounted for 13% of the variance. Greater memory-IIV was significantly associated with being unemployed (β = -.16, SE = .07, P = .020, Exp(B) = 0.85; 95% CI, 0.74-0.98).

CONCLUSION

These findings build upon prior work showing that IIV, or cognitive dispersion, is associated with important functional outcomes following mTBI, including employment status. Future studies are needed to verify these findings, but the present study suggests that IIV indices offer a clinically meaningful marker of cognitive functioning and should be considered when evaluating functional outcomes following head trauma.

Insight into intraindividual variability across neuropsychological tests and its association with cognitive dysfunction in patients with lupus

Objective

Dispersion, or variability in an individual’s performance across multiple tasks at a single assessment visit, has been associated with cognitive dysfunction (CD) in many neurodegenerative and neurodevelopmental disorders. We aimed to compute a dispersion score using neuropsychological battery (NB) tests and determine its association with CD in patients with SLE.

Methods

CD was defined as a z-score of ≤−1.5 on ≥2 domains of the NB. To compute a type of dispersion score known as the intraindividual SD (ISD), the SD of age-adjusted and sex-adjusted z-scores was calculated for each visit in each patient. To estimate the association between ISD and cognitive status (CD and non-CD), we used multilevel logistic regression, adjusting for clinically important covariates.

Results

A total of 301 adult patients with SLE completed the NB at baseline, 187 of whom were reassessed at 6 months and 189 at 12 months. CD was observed in 35.2% of patients at baseline, 27.8% at 6 months and 28.0% at 12 months. Prior to covariate adjustment, the mean ISD for non-CD was 1.10±0.31 compared with 1.50±0.70 for CD. After adjusting for ethnicity, education, employment, socioeconomic status and anxiety/depression, there was a statistically significant association between ISD and CD (OR for one-unit increase in ISD: 13.56, 95% CI 4.80 to 38.31; OR for 1/10th-unit increase in ISD: 1.30, 95% CI 1.17 to 1.44). Findings were valid across multiple sensitivity analyses.

Conclusion

This is the first study to show that patients with SLE who were classified as having CD by the NB had more variability across the NB tests (ie, higher ISD score) compared with those who were not classified as having CD.

Number of Concussions Does Not Affect Treatment Response to Cognitive Rehabilitation Interventions Following Mild TBI in Military Service Members

OBJECTIVE

The study objective was to determine whether number of concussions would affect symptom improvement following cognitive rehabilitation (CR) interventions.

METHOD

Service members (N = 126) with concussion history completed a 6-week randomized control trial of CR interventions. Participants were stratified based on self-reported lifetime concussion frequency. Outcome measures included the Paced Auditory Serial Addition Test (PASAT), the Global Severity Index (GSI) from the Symptom Checklist-90-Revised, and the Key Behaviors Change Inventory (KBCI).

RESULTS

Mixed-model analyses of variance revealed a significant main effect for time on cognitive, psychological, and neurobehavioral functioning. A significant main effect for the number of concussions was observed for GSI and KBCI, but not PASAT. Interactions between the number of concussions and time were not significant for any of the outcome variables.

CONCLUSIONS

Over the 6-week interval, improvements were found for all participants across all outcome measures. Number of concussions did not affect improvements over time.

The role of intraindividual cognitive variability in posttraumatic stress syndromes and cognitive aging: a literature search and proposed research agenda

OBJECTIVES

Cognitive impairments are directly related to severity of symptoms and are a primary cause for functional impairment. Intraindividual cognitive variability likely plays a role in both risk and resiliency from symptoms. In fact, such cognitive variability may be an earlier marker of cognitive decline and emergent psychiatric symptoms than traditional psychiatric or behavioral symptoms. Here, our objectives were to survey the literature linking intraindividual cognitive variability, trauma, and dementia and to suggest a potential research agenda.

DESIGN

A wide body of literature suggests that exposure to major stressors is associated with poorer cognitive performance, with intraindividual cognitive variability in particular linked to the development of posttraumatic stress disorder (PTSD) in the aftermath of severe trauma.

MEASUREMENTS

In this narrative review, we survey the empirical studies to date that evaluate the connection between intraindividual cognitive variability, PTSD, and pathological aging including dementia.

RESULTS

The literature suggests that reaction time (RT) variability within an individual may predict future cognitive impairment, including premature cognitive aging, and is significantly associated with PTSD symptoms.

CONCLUSIONS

Based on our findings, we argue that intraindividual RT variability may serve as a common pathological indicator for trauma-related dementia risk and should be investigated in future studies.

Elevated Intraindividual Variability in Executive Functions and Associations with White Matter Microstructure in Veterans with Mild Traumatic Brain Injury

OBJECTIVE

We examined whether intraindividual variability (IIV) across tests of executive functions (EF-IIV) is elevated in Veterans with a history of mild traumatic brain injury (mTBI) relative to military controls (MCs) without a history of mTBI. We also explored relationships among EF-IIV, white matter microstructure, and posttraumatic stress disorder (PTSD) symptoms.

METHOD

A total of 77 Veterans (mTBI = 43, MCs = 34) completed neuropsychological testing, diffusion tensor imaging (DTI), and PTSD symptom ratings. EF-IIV was calculated as the standard deviation across six tests of EF, along with an EF-Mean composite. DSI Studio connectometry analysis identified white matter tracts significantly associated with EF-IIV according to generalized fractional anisotropy (GFA).

RESULTS

After adjusting for EF-Mean and PTSD symptoms, the mTBI group showed significantly higher EF-IIV than MCs. Groups did not differ on EF-Mean after adjusting for PTSD symptoms. Across groups, PTSD symptoms significantly negatively correlated with EF-Mean, but not with EF-IIV. EF-IIV significantly negatively correlated with GFA in multiple white matter pathways connecting frontal and more posterior regions.

CONCLUSIONS

Veterans with mTBI demonstrated significantly greater IIV across EF tests compared to MCs, even after adjusting for mean group differences on those measures as well as PTSD severity. Findings suggest that, in contrast to analyses that explore effects of mean performance across tests, discrepancy analyses may capture unique variance in neuropsychological performance and more sensitively capture cognitive disruption in Veterans with mTBI histories. Importantly, findings show that EF-IIV is negatively associated with the microstructure of white matter pathways interconnecting cortical regions that mediate executive function and attentional processes.

The relationship between neuropsychological dispersion, processing speed and memory after electrical injury

Introduction: Previous studies of neuropsychological performance in electrical injury (EI) patients have produced evidence of deficits in various cognitive domains, but studies have yet to investigate relationships among performance in cognitive domains post-EI. This study examined whether dispersion among neuropsychological test scores was associated with injury parameters and neuropsychological performance in EI patients. Additionally, we examined whether dispersion, processing speed and/or executive abilities explain variance in episodic verbal and visual memory performance among EI patients.Method: Data from 52 post-acute EI patients undergoing outpatient evaluation with objectively-verified valid neuropsychological test performance were examined. Tests included measures of verbal and visual memory, processing speed, and executive functioning. Dispersion was calculated from executive functioning and processing speed scores.Results: Dispersion was not related to mean performance or injury characteristics, but was significantly negatively correlated with performance on a test of processing speed, suggesting that increased dispersion is associated with reduced cognitive efficiency post-EI. Delayed visual memory was related to both dispersion scores and processing speed. Stepwise regression equations predicting delayed memory determined that processing speed most significantly predicted delayed visual memory, even after controlling for immediate visual memory. No significant relationships emerged between verbal memory and non-memory neuropsychological scores.Conclusions: This is the first study to examine neuropsychological dispersion and relationships among domains of cognitive functioning in EI. Current results suggested that neuropsychological dispersion is not a marker of general functioning or severity of injury in EI patients, but may represent more specific processing speed abilities. Processing speed predicts delayed visual memory performance in EI patients, which should be considered in interpreting test scores during evaluations.

Estimating Repeat Traumatic Brain Injury in the U.S. Military, 2015-2017

INTRODUCTION

Traumatic brain injury (TBI) is a significant health issue among deployed and non-deployed U.S. military service members (SMs). Since 2000, an estimated 413,858 SMs have been diagnosed with at least one TBI. Due to the difficulty in distinguishing new incident TBIs from follow-up TBI-related medical encounters in the Military Health System (MHS), the official TBI case definition also includes an incidence rule considering an individual an incident case only once per lifetime. We sought to examine patterns in medical records of SMs with at least one TBI encounter, in an effort to identify repeat TBIs in individual SMs and to estimate the incidence of repeat TBIs within the study cohort as a whole.

MATERIALS AND METHODS

Using the official DoD TBI case definition, we obtained a list of SMs who sustained their first active duty TBI between October 1, 2015, and September 30, 2017. We identified the SM's diagnosing encounter (index TBI). Subsequently, we identified patterns associated with diagnosing medical encounters, as opposed to encounters associated with follow-up TBI care. We flagged external cause of injury records and the presence of TBI-related symptom codes at the diagnosing encounter. Traumatic brain injury-related symptoms included memory issues, alteration of cognition, hearing loss, vertigo, headache, anxiety, depression, emotional lability, weakness, insomnia, and vision disturbance. Data discovery results were shared with a group of clinicians at the Defense and Veterans Brain Injury Center, and the list of variables was further refined based on clinical expertise. Subsequently, we conducted stepwise logistic regression, and best fitting model was used to create a probability score to be applied to all TBI-related medical encounters. To validate the accuracy of the model-derived probability score, a stratified random sample of medical records was reviewed by trained clinician. At the 0.5 probability cutoff point, the model had an area under the curve of 0.69. We applied the final model portability scores to all identified TBI encounters to estimate the incidence of repeat TBI within the cohort.

RESULTS

Between October 1, 2015, and September 30, 2017, we identified 36,440 SMs and their first lifetime TBI encounter. Study follow-up period was 2 years. Predictors of repeat TBI (rTBI) encounters included the presence of TBI diagnosis extender codes "A" (odds ratio [OR] = 4.67, 95% CI 2.15-10.12); W and V series codes (OR = 4.05, 95% CI 2.05-7.95 and OR = 2.86, 95% CI 1.40-5.83, respectively); patient's disposition at home/quarters; and admission or immediate referral (OR = 3.67, 95% CI 1.79-7.51). Number of diagnosis codes in patient's medical record was inversely associated with a repeat TBI encounter (OR = 0.84, 95% CI 0.76-0.96). Applying model-derived probability score onto identified medical records, we estimate that 804 unique SMs sustained an rTBI during the follow-up period, yielding a rate of 260 rTBIs per 10,000 person-years or approximately 2.32% of SMs annually.

CONCLUSION

Probability scores based on statistical modeling can provide reasonable estimates of repeat incidences of TBI using medical billing data when formerly only the first TBI was thought to be measurable. With 100% sensitivity and 69% specificity, application of these models can inform estimates of repeat TBI across the MHS. This effort shows initial success if estimating repeat TBI, and further modeling work is encouraged to increase the predictive characteristics of the models as these efforts show promise in estimating repeat TBI across the MHS.

Repetitive mTBI is associated with age-related reductions in cerebral blood flow but not cortical thickness

Mild traumatic brain injury (mTBI) is a risk factor for Alzheimer's disease (AD), and evidence suggests cerebrovascular dysregulation initiates deleterious neurodegenerative cascades. We examined whether mTBI history alters cerebral blood flow (CBF) and cortical thickness in regions vulnerable to early AD-related changes. Seventy-four young to middle-aged Veterans (mean age = 34, range = 23-48) underwent brain scans. Participants were divided into: (1) Veteran Controls (n = 27), (2) 1-2 mTBIs (n = 26), and (2) 3+ mTBIs (n = 21) groups. Resting CBF was measured using MP-PCASL. T1 structural scans were processed with FreeSurfer. CBF and cortical thickness estimates were extracted from nine AD-vulnerable regions. Regression analyses examined whether mTBI moderated the association between age, CBF, and cortical thickness. Regressions adjusting for sex and posttraumatic stress revealed mTBI moderated the association between age and CBF of the precuneus as well as superior and inferior parietal cortices (p's < .05); increasing age was associated with lower CBF in the 3+ mTBIs group, but not in the VCs or 1-2 mTBIs groups. mTBI did not moderate associations between age and cortical thickness (p's >.05). Repetitive mTBI is associated with cerebrovascular dysfunction in AD-vulnerable regions and may accelerate pathological aging trajectories.

Associations Between Multiple Remote Mild TBIs and Objective Neuropsychological Functioning and Subjective Symptoms in Combat-Exposed Veterans

OBJECTIVE

The purpose of this study was to evaluate relationships between multiple mild traumatic brain injuries (mTBIs) and objective and subjective clinical outcomes in a sample of combat-exposed Veterans, adjusting for psychiatric distress and combat exposure.

METHOD

In this cross-sectional study, 73 combat-exposed Iraq/Afghanistan Veterans were divided into three groups based on mTBI history: 0 mTBIs (n = 31), 1-2 mTBIs (n = 21), and 3+ mTBIs (n = 21). Veterans with mTBI were assessed, on average, 7.78 years following their most recent mTBI. Participants underwent neuropsychological testing and completed self-report measures assessing neurobehavioral, sleep, and pain symptoms.

RESULTS

MANCOVAs adjusting for psychiatric distress and combat exposure showed no group differences on objective measures of attention/working memory, executive functioning, memory, and processing speed (all p's > .05; ηp2 = .00-.06). In contrast, there were significant group differences on neurobehavioral symptoms (p's = < .001-.036; ηp2 = .09-.43), sleep difficulties (p = .037; ηp2 = .09), and pain symptoms (p < .001; ηp2 = .21). Pairwise comparisons generally showed that the 3+ mTBI group self-reported the most severe symptoms, followed by comparable symptom reporting between the 0 and 1-2 mTBI groups.

CONCLUSIONS

History of multiple, remote mTBIs is associated with elevated subjective symptoms but not objective neuropsychological functioning in combat-exposed Veterans. These results advance understanding of the long-term consequences of repetitive mTBI in this population and suggest that Veterans with 3+ mTBIs may especially benefit from tailored treatments aimed at ameliorating specific neurobehavioral, sleep, and pain symptoms.

Neuropsychological Impact of Trauma-Related Mental Illnesses: A Systematic Review of Clinically Meaningful Results

A trauma history is present in approximately 90% of adults in the United States. Comparatively, lifetime post-traumatic stress disorder (PTSD) prevalence is only 8.3% (Kilpatrick et al. Journal of Traumatic Stress, 26, 537-547, 2013). A neuropsychological understanding of trauma is essential to effective trauma-informed assessments and treatments. Prior reviews have focused on PTSD, specific neuropsychological domains, and statistically rather than clinically significant results. The current systematic review investigated standardized test performance across neuropsychological domains in participants with trauma histories and any psychiatric diagnosis. The review was conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. From 2350 records, the search returned 21 eligible studies: 8 for combat trauma, 2 for childhood trauma, 2 for intimate partner violence and sexual assault, 2 for accidental trauma, 1 for refugee trauma, and 6 for unspecified trauma. Mean neuropsychological scores ranged from low to high average, with one mean verbal memory score in the borderline range. These findings diverge from reports of between-group differences or experimental task performance, which suggest greater levels of static cognitive impairment. Current results are limited by lack of distinction between trauma types in the literature, a dearth of cognitive domains examined, wide use of self-report trauma measures, and publication and outcome reporting biases. Clinical implications for assessment and rehabilitation are discussed in relation to clinical significance, state versus trait based changes, intra-individual variability, changes from pre- to post-trauma, and within-group variability in resilience. Future directions are recommended in consideration of cultural factors, prospective and follow-up designs, and psychiatric diagnosis.

An observational study of trait and state fatigue, and their relation to cognitive fatigability and saccade performance

Aim:

Different fatigue measurements and their relation to saccadic functions were investigated in 15 patients with a mild traumatic brain injury (mTBI) and 15 orthopedic controls.

Materials & methods:

State fatigue was measured with the Fatigue Severity Scale and trait fatigue with the question on fatigue in the Rivermead Post Concussion Questionnaire and fatigability as decreased performance over time on a neuropsychological measure.

Results:

Patients with an mTBI scored significantly higher in state fatigue and showed more fatigability compared with the orthopedic controls. Among patients with mTBI, state fatigue correlated with prosaccade latency and cognitive fatigability, while trait fatigue correlated with anxiety and antisaccade latency and variability.

Conclusion:

This pilot study indicates that saccade measurements might, in the future, be useful in the understanding of fatigue and in the search for prognostic factors after mTBI.

Acute Post-Traumatic Sleep May Define Vulnerability to a Second Traumatic Brain Injury in Mice

Chronic neurological impairments can manifest from repetitive traumatic brain injury (rTBI), particularly when subsequent injuries occur before the initial injury completely heals. Herein, we apply post-traumatic sleep as a physiological biomarker of vulnerability, hypothesizing that a second TBI during post-traumatic sleep worsens neurological and histological outcomes compared to one TBI or a second TBI after post-traumatic sleep subsides. Mice received sham or diffuse TBI by midline fluid percussion injury; brain-injured mice received one TBI or rTBIs at 3- or 9-h intervals. Over 40 h post-injury, injured mice slept more than shams. Functional assessments indicated lower latencies on rotarod and increased Neurological Severity Scores for mice with rTBIs within 3 h. Anxiety-like behaviors in the open field task were increased for mice with rTBIs at 3 h. Based on pixel density of silver accumulation, neuropathology was greater at 28 days post-injury (DPI) in rTBI groups than sham and single TBI. Cortical microglia morphology was quantified and mice receiving rTBI were de-ramified at 14 DPI compared to shams and mice receiving a single TBI, suggesting robust microglial response in rTBI groups. Orexin-A-positive cells were sustained in the lateral hypothalamus with no loss detected, indicating that loss of wake-promoting neurons did not contribute to post-traumatic sleep. Thus, duration of post-traumatic sleep is a period of vulnerability that results in exacerbated injury from rTBI. Monitoring individual post-traumatic sleep is a potential clinical tool for personalized TBI management, where regular sleep patterns may inform rehabilitative strategies and return-to-activity guidelines.