Risk for late-life re-injury, dementia and death among individuals with traumatic brain injury: a population-based study

Impact of prior axonal injury on subsequent injury during brain tissue stretching - A mesoscale computational approach

Epidemiology studies of traumatic brain injury (TBI) show individuals with a prior history of TBI experience an increased risk of future TBI with a significantly more detrimental outcome. But the mechanisms through which prior head injuries may affect risks of injury during future head insults have not been identified. In this work, we show that prior brain tissue injury in the form of mechanically induced axonal injury and glial scar formation can facilitate future mechanically induced tissue injury. To achieve this, we use finite element computational models of brain tissue and a history-dependent pathophysiology-based mechanically-induced axonal injury threshold to determine the evolution of axonal injury and scar tissue formation and their effects on future brain tissue stretching. We find that due to the reduced stiffness of injured tissue and glial scars, the existence of prior injury can increase the risk of future injury in the vicinity of prior injury during future brain tissue stretching. The softer brain scar tissue is shown to increase the strain and strain rate in its vicinity by as much as 40% in its vicinity during dynamic stretching that reduces the global strain required to induce injury by 20% when deformed at 15 s-1 strain rate. The results of this work highlight the need to account for patient history when determining the risk of brain injury.

Age Suppresses the Association Between Traumatic Brain Injury Severity and Functional Outcomes: A Study Using the NIDILRR TBIMS Dataset

OBJECTIVES

Recovery from traumatic brain injury (TBI) is extremely difficult to predict, with TBI severity usually demonstrating weak predictive validity for functional or other outcomes. A possible explanation may lie in the statistical phenomenon called suppression, according to which a third variable masks the true association between predictor and outcome, making it appear weaker than it actually is. Age at injury is a strong candidate as a suppressor because of its well-established main and moderating effects on TBI outcomes. We tested age at injury as a possible suppressor in the predictive chain of effects between TBI severity and functional disability, up to 10 years post-TBI.

SETTING

Follow-up interviews were conducted during telephone interviews.

PARTICIPANTS

We used data from the 2020 NDILRR Model Systems National Dataset for 4 successive follow-up interviews: year 1 (n = 10,734), year 2 (n = 9174), year 5 (n = 6,201), and year 10 (n = 3027).

DESIGN

Successive cross-sectional multiple regression analyses.

MAIN MEASURES

Injury severity was operationalized using a categorical variable representing duration of posttrauma amnesia. The Glasgow Outcomes Scale-Extended (GOS-E) operationally defined functioning. Sociodemographic characteristics having significant bivariate correlations with GOS-E were included.

RESULTS

Entry of age at injury into the regression models significantly increases the association between TBI severity and functioning up to 10 years post-TBI.

CONCLUSIONS

Age at injury is a suppressor variable, masking the true effect of injury severity on functional outcomes. Identifying the mediators of this suppression effect is an important direction for TBI rehabilitation research.

Perceptions of communication recovery following traumatic brain injury: A qualitative investigation across 2 years

BACKGROUND

Exploring the perceptions of individuals with traumatic brain injury (TBI) towards their brain injury recovery across the continuum of care may offer insights to support engagement with rehabilitation services. Illness narratives are a potentially valuable avenue for examining perceptions of recovery that may influence engagement.

AIMS

The aim of this study is to explore the perspective of individuals with severe TBI towards their communication, brain injury and recovery experiences at 6 months, 1 year and 2 years post-injury.

METHODS & PROCEDURES

Discourse samples were obtained from 12 participants with severe TBI at 6 months, 1 year and 2 years following injury. A standardised protocol was used to elicit responses relating to perceptions of communication, the brain injury narrative, and perceptions of recovery facilitators. A thematic analysis of the discourse samples was completed.

OUTCOMES & RESULTS

Three overarching themes were identified: experiences of communication recovery are diverse (Theme 1), varied experiences of recovery and rehabilitation (Theme 2), and continuous and lifelong journey of recovery (Theme 3). Primary communication concerns included presence of anomia, dysarthria, conversational topic difficulties, impacts of fatigue and memory difficulties. Illness narratives revealed the importance of re-establishing a sense of self and the perceived importance of a strong social network post-injury.

CONCLUSIONS & IMPLICATIONS

The varied nature of communication challenges and recovery after TBI highlights the need for holistic, multidisciplinary support as well as inclusion of family and friends in the recovery process. Social communication intervention is a perceived priority area for individuals with TBI. Illness narratives may also play a valuable role in therapy and help to shape post-injury identity. Managing the impacts of fatigue on communication and encouraging individuals to take ownership over their recovery and treatment may also help to improve patient outcomes. Supporting individuals to construct positive brain injury narratives that reaffirm a sense of self and include perspectives of family and friends may offer a potential future avenue for rehabilitation. Tailored but flexible, team-based service delivery models for individuals with TBI that span from acute to long-term care are warranted. WHAT THIS STUDY ADDS?: What is already known on this subject Communication recovery from traumatic brain injury (TBI) is complex and multifaceted. The perceptions of individuals with TBI toward their communication recovery is largely unknown. To establish rehabilitation services that meet the needs of these individuals, we need to understand how they experience communication recovery. What this paper adds to existing knowledge Social communication interventions were perceived as a priority for intervention by individuals with TBI. Fatigue was identified as perceived barrier to communication recovery. Taking ownership over one's recovery process was revealed as a facilitator of recovery. Illness narratives were found to strengthen post-injury identity over time. What are the potential or actual clinical implications of this work? Speech pathologists should prioritise social communication interventions and fatigue management for communication. Facilitating ownership of the recovery process and offering long-term supports are key aspects of treatment. Supporting positive illness narratives as part of treatment may facilitate post-injury identity construction.

Association Between Participation and Satisfaction With Life Over Time in Older Adults With Traumatic Brain Injury: A TBI Model Systems Study

OBJECTIVE

To examine the association between participation and satisfaction with life at 1, 2, 5, and 10 years after traumatic brain injury (TBI) in older adults.

SETTING

Community.

PARTICIPANTS

Participants (N = 2362) who sustained complicated mild to severe TBI, requiring inpatient rehabilitation, at age 60 years or older and had follow-up data on participation and satisfaction with life for at least 1 follow-up time point across 1, 2, 5, and 10 years. Age at each time period was categorized as 60 to 64 years, 65 to 75 years, and 75 years or older.

DESIGN

Secondary data analysis of a large multicenter database.

MAIN MEASURES

Three domains (Productivity, Social Relations, Out and About) of the Participation Assessment With Recombined Tools-Objective (PART-O); Satisfaction With Life Scale (SWLS).

RESULTS

SWLS increased over the 10 years after TBI and was significantly associated with greater frequency of participation across all domains. There was a significant interaction between age and PART-O Social Relations such that there was a weaker relationship between Social Relations and SWLS in the oldest group (75 years or older). There was no interaction between Productivity or Out and About and age, but greater participation in both of these domains was associated with greater life satisfaction across age groups.

CONCLUSIONS

These findings indicate that greater participation is associated with increased satisfaction with life in older adults, across all participation domains over the first 10 years postinjury, suggesting that rehabilitation should target improving participation even in older adults. The decreased association of social relations with satisfaction with life in the oldest age group suggests that frequency of social relations may not be as important for life satisfaction in the oldest adults, but quality may still be important.

Blood Markers in Relation to a History of Traumatic Brain Injury Across Stages of Cognitive Impairment in a Diverse Cohort

BACKGROUND

Traumatic brain injury (TBI) has been linked to multiple pathophysiological processes that could increase risk for Alzheimer's disease and related dementias (ADRD). However, the impact of prior TBI on blood biomarkers for ADRD remains unknown.

OBJECTIVE

Using cross-sectional data, we assessed whether a history of TBI influences serum biomarkers in a diverse cohort (approximately 50% Hispanic) with normal cognition, mild cognitive impairment, or dementia.

METHODS

Levels of glial fibrillary acidic protein (GFAP), neurofilament light (NFL), total tau (T-tau), and ubiquitin carboxy-terminal hydrolase-L1 (UCHL1) were measured for participants across the cognitive spectrum. Participants were categorized based on presence and absence of a history of TBI with loss of consciousness, and study samples were derived through case-control matching. Multivariable general linear models compared concentrations of biomarkers in relation to a history of TBI and smoothing splines modelled biomarkers non-linearly in the cognitively impaired groups as a function of time since symptom onset.

RESULTS

Each biomarker was higher across stages of cognitive impairment, characterized by clinical diagnosis and Mini-Mental State Examination performance, but these associations were not influenced by a history of TBI. However, modelling biomarkers in relation to duration of cognitive symptoms for ADRD showed differences by history of TBI, with only GFAP and UCHL1 being elevated.

CONCLUSIONS

Serum GFAP, NFL, T-tau, and UCHL1 were higher across stages of cognitive impairment in this diverse clinical cohort, regardless of TBI history, though longitudinal investigation of the timing, order, and trajectory of the biomarkers in relation to prior TBI is warranted.

Identification of Factors in Moderate-Severe TBI Related to a Functional Decline in Cognition Decades After Injury

OBJECTIVE

To investigate whether a functional decline in cognitive activities decades after moderate-to-severe traumatic brain injury (m-sTBI) might relate to injury features and/or lifetime health factors, some of which may emerge as consequences of the injury.

DESIGN

Secondary analysis of the TBI Model Systems National Database, a prospective, multi-center, longitudinal study of patients with m-sTBI.

SETTING

TBI Model Systems Centers.

PARTICIPANTS

Included were 732 participants rated on the cognitive subscale of the Functional Independence Measure (FIM Cognitive), a metric for everyday cognitive skills, across 3 time points out to 20 years (visits at 2-, 10-, and 20-year follow-ups; N=732).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURE(S)

FIM Cognitive Scale. Injury characteristics such as timing and features pertaining to severity and health-related factors (eg, alcohol use, socioeconomic status) were examined to discriminate stable from declining participants on the FIM Cognitive Scale using logistic regression.

RESULTS

At 20 years post-injury, there was a low base rate of FIM Cognitive decline (11%, n=78), with most being stable or having meaningful improvement (89%, n=654). Older age at injury, longer duration of post-traumatic amnesia, and presence of repetitive seizures were significant predictors of FIM Cognitive decline in the final model (area under the curve=0.75), while multiple health-related factors that can represent independent co-morbidities or possible consequences of injury were not.

CONCLUSION(S)

The strongest contributors to reported functional decline in cognitive activities later-in-life were related to acute characteristics of m-sTBI and experiencing post-traumatic seizures. Future studies are needed integrating functional with performance-based cognitive assessments to affirm conclusions and identify the timeline and trajectory of cognitive decline.

Screening for Brain Injury Sustained in the Context of Intimate Partner Violence (IPV): Measure Development and Preliminary Utility of the Brain Injury Screening Questionnaire IPV Module

Abstract Intimate partner violence (IPV) is associated with risk for multi-etiology brain injury (BI), including repetitive head impacts, isolated traumatic brain injuries (TBI), and anoxic/hypoxic injury secondary to nonfatal strangulation (NFS). IPV-related injuries are often unreported, but evidence suggests that survivors are more likely to report when asked directly. There are currently no validated tools for screening of brain injury related to IPV that meet World Health Organization guidelines for this population. Here, we describe measure development methods and preliminary utility of the Brain Injury Screening Questionnaire IPV (BISQ-IPV) module. We culled items from existing IPV and TBI screening tools and sought two rounds of stakeholder feedback regarding content coverage, terminology, and safety of administration. The resulting stakeholder-informed BISQ-IPV module is a seven-item self-report measure that uses contextual cues (e.g., being shoved, shaken, strangled) to query lifetime history of IPV-related head/neck injury. We introduced the BISQ-IPV module into the Late Effects of TBI (LETBI) study to investigate rates of violent and IPV-specific head/neck injury reporting in a TBI sample. Among those who completed the BISQ-IPV module (n = 142), 8% of the sample (and 20% of women) reported IPV-related TBI, and 15% of the sample (34% of women) reported IPV-related head or neck injury events that did not result in loss or alteration of consciousness. No men reported NFS; one woman reported inferred BI secondary to NFS, and 6% of women reported NFS events. Those who endorsed IPV-BI were all women, many were highly educated, and many reported low incomes. We then compared reporting of violent TBIs and head/neck injury events among individuals who completed the core BISQ wherein IPV is not specifically queried (administered from 2015-2018; n = 156) to that of individuals who completed the core BISQ preceded by the BISQ-IPV module (BISQ+IPV, administered from 2019-2021; n = 142). We found that 9% of those who completed the core BISQ reported violent TBI (e.g., abuse, assault), whereas 19% of those who completed the BISQ+IPV immediately preceding the core BISQ reported non-IPV-related violent TBI on the core BISQ. These findings suggest that standard TBI screening tools are inadequate for identifying IPV-BI and structured cueing of IPV-related contexts yields greater reporting of both IPV- and non-IPV-related violent BI. When not queried directly, IPV-BI remains a hidden variable in TBI research studies.

Longitudinal Recovery Following Repetitive Traumatic Brain Injury

Importance

One traumatic brain injury (TBI) increases the risk of subsequent TBIs. Research on longitudinal outcomes of civilian repetitive TBIs is limited.

Objective

To investigate associations between sustaining 1 or more TBIs (ie, postindex TBIs) after study enrollment (ie, index TBIs) and multidimensional outcomes at 1 year and 3 to 7 years.

Design, Setting, and Participants

This cohort study included participants presenting to emergency departments enrolled within 24 hours of TBI in the prospective, 18-center Transforming Research and Clinical Knowledge in Traumatic Brain Injury (TRACK-TBI) study (enrollment years, February 2014 to July 2020). Participants who completed outcome assessments at 1 year and 3 to 7 years were included. Data were analyzed from September 2022 to August 2023.

Exposures

Postindex TBI(s).

Main Outcomes and Measures

Demographic and clinical factors, prior TBI (ie, preindex TBI), and functional (Glasgow Outcome Scale-Extended [GOSE]), postconcussive (Rivermead Post-Concussion Symptoms Questionnaire [RPQ]), psychological distress (Brief Symptom Inventory-18 [BSI-18]), depressive (Patient Health Questionnaire-9 [PHQ-9]), posttraumatic stress disorder (PTSD; PTSD Checklist for DSM-5 [PCL-5]), and health-related quality-of-life (Quality of Life After Brain Injury-Overall Scale [QOLIBRI-OS]) outcomes were assessed. Adjusted mean differences (aMDs) and adjusted relative risks are reported with 95% CIs.

Results

Of 2417 TRACK-TBI participants, 1572 completed the outcomes assessment at 1 year (1049 [66.7%] male; mean [SD] age, 41.6 [17.5] years) and 1084 completed the outcomes assessment at 3 to 7 years (714 [65.9%] male; mean [SD] age, 40.6 [17.0] years). At 1 year, a total of 60 participants (4%) were Asian, 255 (16%) were Black, 1213 (77%) were White, 39 (2%) were another race, and 5 (0.3%) had unknown race. At 3 to 7 years, 39 (4%) were Asian, 149 (14%) were Black, 868 (80%) were White, 26 (2%) had another race, and 2 (0.2%) had unknown race. A total of 50 (3.2%) and 132 (12.2%) reported 1 or more postindex TBIs at 1 year and 3 to 7 years, respectively. Risk factors for postindex TBI were psychiatric history, preindex TBI, and extracranial injury severity. At 1 year, compared with those without postindex TBI, participants with postindex TBI had worse functional recovery (GOSE score of 8: adjusted relative risk, 0.57; 95% CI, 0.34-0.96) and health-related quality of life (QOLIBRI-OS: aMD, -15.9; 95% CI, -22.6 to -9.1), and greater postconcussive symptoms (RPQ: aMD, 8.1; 95% CI, 4.2-11.9), psychological distress symptoms (BSI-18: aMD, 5.3; 95% CI, 2.1-8.6), depression symptoms (PHQ-9: aMD, 3.0; 95% CI, 1.5-4.4), and PTSD symptoms (PCL-5: aMD, 7.8; 95% CI, 3.2-12.4). At 3 to 7 years, these associations remained statistically significant. Multiple (2 or more) postindex TBIs were associated with poorer outcomes across all domains.

Conclusions and Relevance

In this cohort study of patients with acute TBI, postindex TBI was associated with worse symptomatology across outcome domains at 1 year and 3 to 7 years postinjury, and there was a dose-dependent response with multiple postindex TBIs. These results underscore the critical need to provide TBI prevention, education, counseling, and follow-up care to at-risk patients.

Clinical Updates in Mild Traumatic Brain Injury (Concussion)

Traumatic brain injury (TBI) affects > 3 million people in the United States annually. Although the number of deaths related to severe TBIs has stabalized, mild TBIs, often termed concussions, are increasing. As evidence indicates that a significant proportion of these mild injuries are associated with long-lasting functional deficits that impact work performance, social integration, and may predispose to later cognitive decline, it is important that we (a) recognize these injuries, (b) identify those at highest risk of poor recovery, and (c) initiate appropriate treatments promptly. We discuss the epidemiology of TBI, the most common persistent symptoms, and treatment approaches.

Distal and Proximal Predictors of Rehospitalization Over 10 Years Among Survivors of TBI: A National Institute on Disability, Independent Living, and Rehabilitation Research Traumatic Brain Injury Model Systems Study

OBJECTIVE

To describe the rates and causes of rehospitalization over a 10-year period following a moderate-severe traumatic brain injury (TBI) utilizing the Healthcare Cost and Utilization Project (HCUP) diagnostic coding scheme.

SETTING

TBI Model Systems centers.

PARTICIPANTS

Individuals 16 years and older with a primary diagnosis of TBI.

DESIGN

Prospective cohort study.

MAIN MEASURES

Rehospitalization (and reason for rehospitalization) as reported by participants or their proxies during follow-up telephone interviews at 1, 2, 5, and 10 years postinjury.

RESULTS

The greatest number of rehospitalizations occurred in the first year postinjury (23.4% of the sample), and the rates of rehospitalization remained stable (21.1%-20.9%) at 2 and 5 years postinjury and then decreased slightly (18.6%) at 10 years postinjury. Reasons for rehospitalization varied over time, but seizure was the most common reason at 1, 2, and 5 years postinjury. Other common reasons were related to need for procedures (eg, craniotomy or craniectomy) or medical comorbid conditions (eg, diseases of the heart, bacterial infections, or fractures). Multivariable logistic regression models showed that Functional Independence Measure (FIM) Motor score at time of discharge from inpatient rehabilitation was consistently associated with rehospitalization at all time points. Other factors associated with future rehospitalization over time included a history of rehospitalization, presence of seizures, need for craniotomy/craniectomy during acute hospitalization, as well as older age and greater physical and mental health comorbidities.

CONCLUSION

Using diagnostic codes to characterize reasons for rehospitalization may facilitate identification of baseline (eg, FIM Motor score or craniotomy/craniectomy) and proximal (eg, seizures or prior rehospitalization) factors that are associated with rehospitalization. Information about reasons for rehospitalization can aid healthcare system planning. By identifying those recovering from TBI at a higher risk for rehospitalization, providing closer monitoring may help decrease the healthcare burden by preventing rehospitalization.

Group-Based Patterns of Life Satisfaction and Functional Independence over the 10 Years after Traumatic Brain Injury in Older Adults: A Model Systems Study

BACKGROUND

Older adults who sustain a traumatic brain injury (TBI) have been shown to have reduced functional independence and life satisfaction relative to younger individuals with TBI. The purpose of this study was to examine the covarying patterns of functional independence and life satisfaction over the 10 years after TBI in adults who were 60 years of age or older upon injury.

METHOD

Participants were 1841 individuals aged 60 or older at the time of TBI, were enrolled in the longitudinal TBI Model Systems database, and had Functional Independence Measure and Satisfaction with Life Scale scores during at least one time point at 1, 2, 5, and 10 years after TBI.

RESULTS

A k-means cluster analysis identified four distinct group-based longitudinal patterns of these two variables. Three cluster groups suggested that functional independence and life satisfaction generally traveled together over time, with one group showing relatively high functional independence and life satisfaction over time (Cluster 2), one group showing relatively moderate functional independence and life satisfaction (Cluster 4), and one group showing relatively low functional independence and life satisfaction (Cluster 1). Cluster 3 had relatively high functional independence over time but, nonetheless, relatively low life satisfaction; they were also the youngest group upon injury. Participants in Cluster 2 generally had the highest number of weeks of paid competitive employment but lower percentages of underrepresented racial/ethnic minority participants, particularly Black and Hispanic individuals. Women were more likely to be in the cluster with the lowest life satisfaction and functional independence (Cluster 1).

CONCLUSION

Functional independence and life satisfaction generally accompany one another over time in older adults, although this does not always occur, as life satisfaction can still be low in a subgroup of older individuals after TBI with higher functioning. These findings contribute to a better understanding of post-TBI recovery patterns in older adults over time that may inform treatment considerations to improve age-related discrepancies in rehabilitation outcomes.

Telehealth delivery of group-format cognitive rehabilitation to older veterans with TBI: a mixed-methods pilot study

Traumatic brain injury (TBI) is common among Veterans and may interact with aging, increasing risk for negative cognitive, emotional, and functional outcomes. However, no accessible (i.e., in-home) group interventions for TBI targeted to older adults exist. Goal Oriented Attentional Self-Regulation (GOALS) is a manualized, group cognitive rehabilitation training that improves executive function and emotional regulation among Veterans with TBI and healthy older adults. Our objectives were to adapt GOALS for delivery to older Veterans via in-home video telehealth (IVT) and evaluate feasibility and participant-rated acceptability of the telehealth GOALS intervention (TeleGOALS). Six Veterans 69+, with multiple TBIs completed the 10-session intervention in groups of 2. One participant withdrew, and another completed the remaining sessions alone (total n enrolled = 8). Required adaptations were noted; questionnaire responses were quantified; and feedback was analyzed and coded to identify themes. Quantitative and qualitative methods were used to examine feasibility (i.e., recruitment and retention) and participant-rated acceptability. Minimal adaptations were required for IVT delivery. Key themes emerged: (a) the importance of telehealth logistics, (b) facilitators' roles in prioritizing interpersonal connection, and (c) telehealth's capability to create opportunities for community reintegration. Thematic saturation (the point at which feedback from respondents is consistent and no further adaptations are required) was achieved. Participants stated they would likely recommend TeleGOALS to other Veterans. Although further study with a larger, more diverse sample is required, the adapted TeleGOALS intervention appears highly feasible and acceptable for older Veterans with TBI able and willing to participate in a group-format IVT intervention.

The Role of Neuroimaging in Evolving TBI Research and Clinical Practice

Neuroimaging technologies such as computed tomography (CT) and magnetic resonance imaging (MRI) have been widely adopted in the clinical diagnosis and management of traumatic brain injury (TBI), particularly at the more acute and severe levels of injury. Additionally, a number of advanced applications of MRI have been employed in TBI-related clinical research with great promise, and researchers have used these techniques to better understand underlying mechanisms, progression of secondary injury and tissue perturbation over time, and relation of focal and diffuse injury to later outcome. However, the acquisition and analysis time, the cost of these and other imaging modalities, and the need for specialized expertise have represented historical barriers in extending these tools in clinical practice. While group studies are important in detecting patterns, heterogeneity among patient presentation and limited sample sizes from which to compare individual level data to well-developed normative data have also played a role in the limited translatability of imaging to wider clinical application. Fortunately, the field of TBI has benefitted from increased public and scientific awareness of the prevalence and impact of TBI, particularly in head injury related to recent military conflicts and sport-related concussion. This awareness parallels an increase in federal funding in the United States and other countries allocated to investigation in these areas. In this article we summarize funding and publication trends since the mainstream adoption of imaging in TBI to elucidate evolving trends and priorities in the application of different techniques and patient populations. We also review recent and ongoing efforts to advance the field through promoting reproducibility, data sharing, big data analytic methods, and team science. Finally, we discuss international collaborative efforts to combine and harmonize neuroimaging, cognitive, and clinical data, both prospectively and retrospectively. Each of these represent unique, but related, efforts that facilitate closing gaps between the use of advanced imaging solely as a research tool and the use of it in clinical diagnosis, prognosis, and treatment planning and monitoring.

Traumatic Brain Injury and Risk of Long-Term Nursing Home Entry among Older Adults: An Analysis of Medicare Administrative Claims Data

Traumatic brain injury (TBI) is a leading cause of injury-related disability among older adults, and there is increasing interest in post-discharge management as this population grows. We evaluated the association between TBI and long-term nursing home (NH) entry among a nationally representative sample of older adults. We identified 207,355 adults aged ≥65 years who received a diagnosis of either a TBI, non-TBI trauma, or were uninjured between January 2008 and June 2015 from a 5% sample of Medicare beneficiaries. The NH entry was operationalized as the first NH admission that resulted in a stay ≥100 days. Time to NH entry was calculated as the difference between the NH entry date and the index date (the date of TBI, non-TBI trauma, or inpatient/outpatient visit in the uninjured group). We used cause-specific Cox proportional hazards models with stabilized inverse probability of exposure weights to model time to NH entry as a function of injury in the presence of death as a competing risk and generated hazard ratios (HR) and 95% confidence intervals (CI). After excluding beneficiaries living in a NH at index, there were 60,600 TBI, 63,762 non-TBI trauma, and 69,893 uninjured beneficiaries in the sample. In weighted models, beneficiaries with TBI entered NHs at higher rates relative to the non-TBI trauma (HR 1.15; 95% CI 1.10, 1.20) and uninjured (HR 1.67; 95% CI 1.60, 1.74) groups. Future research should focus on interventions to retain older adult TBI survivors within the community.

Cognitive impairment following traumatic brain injury in Uganda: Prevalence and associated factors

BACKGROUND

As the burden of dementia continues to rise in sub-Saharan Africa, it is crucial to develop an evidence base for potentially modifiable risk factors such as Traumatic Brain Injury (TBI). Cognitive impairment may result from TBI and since it is an established prodromal form of dementia, we investigated the burden of cognitive impairment and associated factors in persons with a history of TBI in southwestern Uganda.

METHODS

This was a community-based quantitative study with a cross-sectional design among 189 persons with a history of TBI in southwestern Uganda. Data were collected by the research team in March and June 2022 and entered into Kobo Toolbox before being transferred to RStudio version 4.1.0 for cleaning and analysis. Data were analyzed at a 5% level of significance.

RESULTS

Most study participants had some form of cognitive impairment (56.1%), with 43.1% of the participants having mild cognitive impairment (MCI). Cognitive impairment was associated with older age (p-value<0.001); loss of consciousness following the TBI (p-value = 0.019) and a history of tobacco use (p-value = 0.003). As a measure of severity of the TBI, loss of consciousness (aOR = 4.09; CI = 1.57-11.76; p<0.01) and older age (aOR = 1.04; CI = 1.01-1.07; p<0.01) were identified as risk factors for cognitive impairment.

CONCLUSION

There is a high burden of cognitive impairment among individuals with a history of TBI in southwestern Uganda, and most associated risk factors are potentially modifiable. Long-term follow-up of TBI patients would enable early identification of some risks. Patients with TBI could benefit from behavioural modifications such as restriction of alcohol intake and tobacco use to slow down the progression into dementia.

How Traumatic Brain Injury History Relates to Brain Health MRI Markers and Dementia Risk: Findings from the 3C Dijon Cohort

BACKGROUND

The long-term effects of traumatic brain injury (TBI) with loss of consciousness (LOC) on magnetic resonance imaging (MRI) markers of brain health and on dementia risk are still debated.

OBJECTIVE

To investigate the associations of history of TBI with LOC with incident dementia and neuroimaging markers of brain structure and small vessel disease lesions.

METHODS

The analytical sample consisted in 4,144 participants aged 65 and older who were dementia-free at baseline from the Three City -Dijon study. History of TBI with LOC was self-reported at baseline. Clinical Dementia was assessed every two to three years, up to 12 years of follow-up. A subsample of 1,675 participants <80 years old underwent a brain MRI at baseline. We investigated the associations between history of TBI with LOC and 1) incident all cause and Alzheimer's disease (AD) dementia using illness-death models, and 2) neuroimaging markers at baseline.

RESULTS

At baseline, 8.3% of the participants reported a history of TBI with LOC. In fully-adjusted models, participants with a history of TBI with LOC had no statistically significant differences in dementia risk (HR = 0.90, 95% CI = 0.60-1.36) or AD risk (HR = 1.03, 95% CI = 0.69-1.52), compared to participants without TBI history. History of TBI with LOC was associated with lower white matter volume (β= -4.58, p = 0.048), but not with other brain volumes, white matter hyperintensities volume, nor covert brain infarct.

CONCLUSION

This study did not find evidence of an association between history of TBI with LOC and dementia or AD dementia risks over 12-year follow-up, brain atrophy, or markers of small vessel disease.

Association of life-course traumatic brain injury with dementia risk: A nationwide twin study

INTRODUCTION

The impact of life-course traumatic brain injury (TBI) on dementia is unclear.

METHODS

Within the Swedish Twin Registry (STR), 35,312 dementia-free twins were followed for up to 18 years. TBI history was identified via medical records. Data were analyzed using generalized estimating equation (GEE) and conditional logistic regression.

RESULTS

In multi-adjusted GEE models, the odds ratio (OR, 95% confidence interval [CI]) of dementia was 1.27 (1.03-1.57) for TBI at any age, 1.55 (1.04-2.31) for TBI at 50 to 59 years, and 1.67 (1.12-2.49) for TBI at 60 to 69 years. Cardiometabolic diseases (CMDs) increased dementia risk associated with TBI at age 50 to 69 years. The ORs in GEE and conditional logistic regression did not differ significantly (P = .37).

DISCUSSION

TBI, especially between ages 50 and 69 years, is associated with an increased risk of dementia, and this is exacerbated among people with CMDs. Genetic and early-life environmental factors may not account for the TBI-dementia association.

Characterization of the spatial distribution of metals and profile of metalloprotein complexes in a mouse model of repetitive mild traumatic brain injury

Metal dyshomeostasis is a well-established consequence of neurodegenerative diseases and traumatic brain injury. While the significance of metals continues to be uncovered in many neurological disorders, their implication in repetitive mild traumatic brain injury remains uncharted. To address this gap, we characterized the spatial distribution of metal levels (iron, zinc, and copper) using laser ablation-inductively coupled plasma-mass spectrometry, the profile of metal-binding proteins via size exclusion chromatography-inductively coupled plasma-mass spectrometry and the expression of the major iron storing protein ferritin via western blotting. Using a mouse model of repetitive mild traumatic brain injury, 3-month-old male and female C57Bl6 mice received one or five impacts (48 h apart). At 1 month following 5× TBI (traumatic brain injury), iron and ferritin levels were significantly elevated in the contralateral cortex. There was a trend toward increased iron levels in the entire contralateral hemisphere and a reduction in contralateral cortical iron-binding proteins following 1× TBI. No major changes in zinc levels were seen in both hemispheres following 5× or 1× TBI, although there was a reduction in ipsilateral zinc-binding proteins following 5× TBI and a contralateral increase in zinc-binding proteins following 1× TBI. Copper levels were significantly increased in both hemispheres following 5× TBI, without changes in copper-binding proteins. This study shows for the first time that repetitive mild TBI (r-mTBI) leads to metal dyshomeostasis, highlighting its potential involvement in promoting neurodegeneration, which provides a rationale for examining the benefit of metal-targeting drugs, which have shown promising results in neurodegenerative conditions and single TBI, but have yet to be tested following r-mTBI.

Epidemiology and Risk Factors for Dementia

In this article, the authors discuss primarily what is known about the epidemiology of all-cause dementia. Dementia is caused by a complex interplay of genetics, comorbidities, and lifestyle factors, and drug development has been challenging. However, evidence from large, prospective, observational studies has identified a variety of factors that may prevent or delay the onset of dementia. Several of these factors are modifiable and lend themselves to well to treatments currently available. The authors discuss the state of current evidence on dementia risk factors, the most promising avenues, and future directions for dementia prevention and management.

Pathophysiology of Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disease leading to dementia worldwide. While neuritic plaques consisting of aggregated amyloid-beta proteins and neurofibrillary tangles of accumulated tau proteins represent the pathophysiologic hallmarks of AD, numerous processes likely interact with risk and protective factors and one's culture to produce the cognitive loss, neuropsychiatric symptoms, and functional impairments that characterize AD dementia. Recent biomarker and neuroimaging research has revealed how the pathophysiology of AD may lead to symptoms, and as the pathophysiology of AD gains clarity, more potential treatments are emerging that aim to modify the disease and relieve its burden.

Traumatic brain injury and dementia risk in male veteran older twins-Controlling for genetic and early life non-genetic factors

INTRODUCTION

This study leveraged the twin study design, which controls for shared genetic and early life exposures, to investigate the association between traumatic brain injury (TBI) and dementia.

METHODS

Members of the National Academy of Sciences-National Research Council's Twins Registry of World War II male veterans were assigned a cognitive outcome based on a multi-step assessment protocol. History of TBI was obtained via interviews.

RESULTS

Among 8302 individuals, risk of non-Alzheimer's disease (non-AD) dementia was higher in those with TBI (hazard ratio [HR] = 2.00, 95% confidence interval [CI], 0.97-4.12), than for AD (HR = 1.23, 95% CI, 0.76-2.00). To add more control of genetic and shared environmental factors, we analyzed 100 twin pairs discordant for both TBI and dementia onset, and found TBI-associated risk for non-AD dementia increased further (McNemar odds ratio = 2.70; 95% CI, 1.27-6.25).

DISCUSSION

These findings suggest that non-AD mechanisms may underlie the association between TBI and dementia, potentially providing insight into inconsistent results from prior studies.

Predictors of 10-year functional independence trajectories in older adults with traumatic brain injury: A Model Systems study

BACKGROUND

Older adults have the highest traumatic brain injury (TBI)-related morbidity and mortality, and rates in older adults are increasing, chiefly due to falls.

OBJECTIVE

This study used hierarchical linear modeling (HLM) to examine baseline predictors of functional independence trajectories across 1, 2, 5, and 10 years after TBI in older adults.

METHODS

Participants comprised 2,459 individuals aged 60 or older at the time of TBI, enrolled in the longitudinal TBI Model Systems database, and had Functional Independence Measure Motor and Cognitive subscale scores and Glasgow Outcome Scale-Extended scores during at least 1 time point.

RESULTS

Functional independence trajectories generally declined over the 10 years after TBI. Individuals who were older, male, underrepresented minorities, had lower education, were unemployed at time of injury, had no history of substance use disorder, or had difficulties with learning, dressing, and going out of the home prior to the TBI, or longer time in posttraumatic amnesia had lower functional independence trajectories across at least one of the functional independence outcomes.

CONCLUSION

These predictors of functional independence in older adults with TBI may heighten awareness of these factors in treatment planning and long-term health monitoring and ultimately as a way to decrease morbidity and mortality.

Frailty independently predicts unfavorable discharge in non-operative traumatic brain injury: A retrospective single-institution cohort study

BACKGROUND

Frailty is associated with adverse outcomes in traumatically injured geriatric patients but has not been well-studied in geriatric Traumatic Brain Injury (TBI).

OBJECTIVE

To assess relationships between frailty and outcomes after TBI.

METHODS

The records of all patients aged 70 or older admitted from home to the neurosurgical service of a single institution for non-operative TBI between January 2020 and July 2021 were retrospectively reviewed. The primary outcome was adverse discharge disposition (either in-hospital expiration or discharge to skilled nursing facility (SNF), hospice, or home with hospice). Secondary outcomes included major inpatient complication, 30-day readmission, and length of stay.

RESULTS

100 patients were included, 90% of whom presented with Glasgow Coma Score (GCS) 14-15. The mean length of stay was 3.78 days. 7% had an in-hospital complication, and 44% had an unfavorable discharge destination. 49% of patients attended follow-up within 3 months. The rate of readmission within 30 days was 13%. Patients were characterized as low frailty (FRAIL score 0-1, n = 35, 35%) or high frailty (FRAIL score 2-5, n = 65, 65%). In multivariate analysis controlling for age and other factors, frailty category (aOR 2.63, 95CI [1.02, 7.14], p = 0.005) was significantly associated with unfavorable discharge. Frailty was not associated with increased readmission rate, LOS, or rate of complications on uncontrolled univariate analyses.

CONCLUSION

Frailty is associated with increased odds of unfavorable discharge disposition for geriatric patients admitted with TBI.

Gender Differences in Personal and Situational Risk Factors for Traumatic Brain Injury Among Older Adults

OBJECTIVE

To investigate differences between older men and women in Taiwan in personal and situational risk factors for sustaining a traumatic brain injury (TBI) versus soft-tissue injury (STI) due to a fall.

DESIGN

Matched case-control study.

PARTICIPANTS AND SETTINGS

Cases were defined as patients with a primary diagnosis of TBI due to a fall and were identified from those 60 years or older who visited the emergency department (ED) of 3 university-affiliated hospitals in 2015. Matched by the same hospital ED, gender, and time of falling, 3 controls who had no TBI and who had sustained only soft-tissue injury (STI) due to falling were selected for comparison with each case. Personal factors and situational exposures were compared between the control and case groups. In total, 96 cases and 288 controls in men and 72 cases and 216 controls in women participated in this study.

MAIN MEASURES

Personal factors (sociodemographic and lifestyle factors, medical characteristics, and functional abilities) and situational exposures (location, activities before the fall, center-of-mass change, type of fall, falling direction, protective response, and impact during the fall).

RESULTS

In men, after adjusting for other variables, older age (odds ratio [OR] = 1.04), regular alcohol use (OR = 2.03), an indoor fall (OR = 1.92), activity of getting in/out of bed (OR = 2.56), a fall due to dizziness (OR = 4.09), and falling backward (OR = 2.95) were independently associated with a higher odds of TBI. In women, an older age (OR = 1.03), the presence of Parkinson disease (OR = 10.4), activities of toileting (OR = 2.50), getting in/out of bed (OR = 4.90), and negotiating stairs (OR = 7.13), a fall due to dizziness (OR = 5.05), and falling backward (OR = 2.61) were independently associated with a higher odds of TBI.

CONCLUSIONS

Our results demonstrated similarities and differences in personal and situational risk factors for fall-related TBIs versus STIs between older men and women, and gender differences should be considered when developing intervention strategies.

Comparison Groups Matter in Traumatic Brain Injury Research: An Example with Dementia

The association between traumatic brain injury (TBI) and risk for Alzheimer's disease and related dementias (ADRD) has been investigated in multiple studies yet reported effect sizes have varied widely. Large differences in comorbid and demographic characteristics between individuals with and without TBI could result in spurious associations between TBI and poor outcomes, even when control for confounding is attempted. Yet, inadvertent control for post-TBI exposures (e.g., psychological and physical trauma) could result in an underestimate of the effect of TBI. Choice of the unexposed or comparison group is critical to estimating total associated risk. The objective of this study was to highlight how selection of the comparison group impacts estimates of the effect of TBI on risk for ADRD. Using data on veterans aged ≥55 years obtained from the Veterans Health Administration (VA) for years 1999-2019, we compared risk of ADRD between veterans with incident TBI (n=9,440) and 1) the general population of veterans who receive care at the VA (All VA)(n=119,003); 2) veterans who received care at a VA emergency department (VA ED)(n=111,342); and 3) veterans who received care at a VA ED for non-TBI trauma (VA ED NTT)(n=65,710). In inverse probability of treatment weighted models, TBI was associated with increased risk of ADRD compared to All VA (HR 1.94; 95% CI 1.84, 2.04), VA ED (HR 1.42; 95% CI 1.35, 1.50), and VA ED NTT (HR 1.12; 95% CI 1.06, 1.18). The estimated effect of TBI on incident ADRD was strongly impacted by choice of the comparison group.

Age Moderates the Effect of Injury Severity on Functional Trajectories in Traumatic Brain Injury: A Study Using the NIDILRR Traumatic Brain Injury Model Systems National Dataset

Age is a risk factor for a host of poor outcomes following traumatic brain injury (TBI), with some evidence suggesting that age is also a source of excess disability. We tested the extent to which age moderates the effect of injury severity on functional trajectories over 15 years post injury. Data from 11,442 participants from the 2020 National Institute of Disability and Independent Living Rehabiitation Research (NIDILRR) Traumatic Brain Injury Model Systems (TBIMS) National Dataset were analyzed using linear mixed effects models. Injury severity was operationally defined using a composite of Glasgow Coma Scale scores, structural imaging findings, and the number of days with post-trauma amnesia. Functioning was measured using the Glasgow Outcomes Scale-Extended. Age at injury was the hypothesized moderator. Race, ethnicity, sex, education, and marital status served as covariates. The results showed a significant confounder-adjusted effect of injury severity and age of injury on the linear slope in functioning. The age effect was strongest for those with mild TBI. Thus, the effects of injury severity on functional trajectory were found to be moderated by age. To optimize outcomes, TBI rehabilitation should be developed specifically for older patients. Age should also be a major focus in TBI research.

Mild Traumatic Brain Injuries and Future Risk of Developing Alzheimer’s Disease: Systematic Review and Meta-Analysis

Background: Traumatic brain injury (TBI) increases the risk of future dementia and Alzheimer’s disease (AD). However, it is unclear whether this is true for mild TBI (mTBI). Objective: To explore the association between mTBI and subsequent risk of developing AD. Method: We systematically searched four electronic databases from January 1954 to April 2020. We included studies reporting primary data and where mTBI preceded AD by≥5 years. We meta-analyzed included studies for both high quality studies and studies with a follow up of > 10 years. Result: We included 5 of the 10,435 results found. Meta-analysis found a history of mTBI increased risk of AD (pooled relative risk = 1.18, 95% CI 1.11–1.25, N = 3,149,740). The sensitivity analysis including only studies in which mTBI preceded AD by > 10 years, excluded two very large studies and resulted in wider confidence intervals (RR = 2.02, 95% CI 0.66–6.21, N = 2307). Conclusion: There is an increased risk of AD following mTBI. Our findings of increased risk even with mTBI means it cannot be assumed that mild head injuries from sports are harmless. The sensitivity analysis suggests that we cannot exclude reverse causation, and longer follow up times are needed. Implementation of policy to reduce mTBIs, including in children and sportsmen, are urgently needed. Further research is needed on the effect of frequency and age at injury of mTBIs.

Traumatic Brain Injury and Risk of Neurodegenerative Disorder

Traumatic brain injury (TBI), particularly of greater severity (i.e., moderate to severe), has been identified as a risk factor for all-cause dementia and Parkinson's disease, with risk for specific dementia subtypes being more variable. Among the limited studies involving neuropathological (postmortem) confirmation, the association between TBI and risk for neurodegenerative disease increases in complexity, with polypathology often reported on examination. The heterogeneous clinical and neuropathological outcomes associated with TBI are likely reflective of the multifaceted postinjury acute and chronic processes that may contribute to neurodegeneration. Acutely in TBI, axonal injury and disrupted transport influences molecular mechanisms fundamental to the formation of pathological proteins, such as amyloid-β peptide and hyperphosphorylated tau. These protein deposits may develop into amyloid-β plaques, hyperphosphorylated tau-positive neurofibrillary tangles, and dystrophic neurites. These and other characteristic neurodegenerative disease pathologies may then spread across brain regions. The acute immune and neuroinflammatory response involves alteration of microglia, astrocytes, oligodendrocytes, and endothelial cells; release of downstream pro- and anti-inflammatory cytokines and chemokines; and recruitment of peripheral immune cells. Although thought to be neuroprotective and reparative initially, prolongation of these processes may promote neurodegeneration. We review the evidence for TBI as a risk factor for neurodegenerative disorders, including Alzheimer's dementia and Parkinson's disease, in clinical and neuropathological studies. Further, we describe the dynamic interactions between acute response to injury and chronic processes that may be involved in TBI-related pathogenesis and progression of neurodegeneration.

Traumatic Brain Injury and Risk of Alzheimer's Disease and Related Dementias in the Population

BACKGROUND

Epidemiological studies examining associations between traumatic brain injury (TBI) and Alzheimer's disease and related dementias (ADRD) have yielded conflicting results, which may be due to methodological differences.

OBJECTIVE

To examine the relationship between the presence and severity of TBI and risk of ADRD using a population-based cohort with medical record abstraction for confirmation of TBI and ADRD.

METHODS

All TBI events among Olmsted County, Minnesota residents aged > 40 years from 1985-1999 were confirmed by manual review and classified by severity. Each TBI case was randomly matched to two age-, sex-, and non-head injury population-based referents without TBI. For TBI events with non-head trauma, the Trauma Mortality Prediction Model was applied to assign an overall measure of non-head injury severity and corresponding referents were matched on this variable. Medical records were manually abstracted to confirm ADRD diagnosis. Cox proportional hazards models examined the relationship between TBI and severity with risk of ADRD.

RESULTS

A total of 1,418 residents had a confirmed TBI (865 Possible, 450 Probable, and 103 Definite) and were matched to 2,836 referents. When combining all TBI severities, the risk of any ADRD was significantly higher for those with a confirmed TBI compared to referents (HR = 1.32, 95% CI: 1.11, 1.58). Stratifying by TBI severity, Probable (HR = 1.42, 95% CI: 1.05, 1.92) and Possible (HR = 1.29, 95% CI: 1.02-1.62) TBI was associated with an increased risk of ADRD, but not Definite TBI (HR = 1.22, 95% CI: 0.68, 2.18).

CONCLUSION

Our analyses support including TBI as a potential risk factor for developing ADRD.

Traumatic Brain Injury and Risk of Dementia and Alzheimer's Disease: A Systematic Review and Meta-Analysis

INTRODUCTION

Previous studies have investigated the potential role of traumatic brain injury (TBI) in subsequent development of dementia and Alzheimer's disease (AD) but reported inconsistent results. We aim to determine the association between TBI and subsequent occurrence of dementia and AD.

METHODS

We performed a systematic search in PubMed and Web of Science for studies that quantitatively investigated the association between TBI and risk of dementia and AD and were published on or before September 21, 2021. A random-effect model was used to combine the estimates.

RESULTS

Twenty-five eligible articles were included in this meta-analysis. The results suggested that TBI was associated with an increased risk of dementia (pooled odds ratio [OR] = 1.81, 95% confidence interval [CI] = 1.53 - 2.14). However, no association was observed between TBI and Alzheimer's disease (pooled OR = 1.02, 95% CI = 0.91 - 1.15). In the subgroup analysis, TBI with loss of consciousness was not associated with risk of dementia (pooled OR = 0.96, 95% CI = 0.84 - 1.09). Besides, Asian ethnicity, male gender, and mean age of the participants less than 65 were associated with a higher risk of dementia.

CONCLUSION

Our study suggests an increased risk of dementia among individuals with TBI, highlighting the need for more intensive medical monitoring and health education in individuals with TBI. Biological mechanisms linking TBI and the development of dementia are needed in future studies.

Alzheimer's Disease-Related Dementias Summit 2019: National research priorities for the investigation of traumatic brain injury as a risk factor for Alzheimer's Disease and Related Dementias

TBI is a risk factor for later life dementia. Clinical and preclinical studies have elucidated multiple mechanisms through which TBI may influence or exacerbate multiple pathological processes underlying Alzheimer's Disease and Alzheimer's Disease Related Dementias (AD/ADRD). The National Institutes of Health hosts triennial ADRD Summits to inform a national research agenda, and the 2019 ADRD Summit was the first to highlight 'TBI and AD/ADRD Risk' as an emerging topic in the field. A multidisciplinary committee of TBI researchers with relevant expertise reviewed extant literature, identified research gaps and opportunities, and proposed draft research recommendations at the 2019 ADRD Summit. These research recommendations, further refined after broad stakeholder input at the Summit, cover four overall areas: (1) Encourage crosstalk and interdisciplinary collaboration between TBI and dementia researchers, (2) Establish infrastructure to study TBI as a risk factor for AD/ADRD, (3) Promote basic and clinical research examining the development and progression of TBI AD/ADRD neuropathologies and associated clinical symptoms, and (4) Characterize the clinical phenotype of progressive dementia associated with TBI and develop non-invasive diagnostic approaches. These recommendations recognize a need to strengthen communication and build frameworks to connect the complexity of TBI with rapidly evolving AD/ADRD research. Recommendations acknowledge TBI as a clinically and pathologically heterogeneous disease whose associations with AD/ADRDs remain incompletely understood. The recommendations highlight the scientific advantage of investigating AD/ADRD in the context of a known TBI exposure, the study of which can directly inform on disease mechanisms and treatment targets for AD/ADRDs with shared common pathways.

Association of remote mild traumatic brain injury with cortical amyloid burden in clinically normal older adults

We investigated whether clinically normal older adults with remote, mild traumatic brain injury (mTBI) show evidence of higher cortical Aβ burden. Our study included 134 clinically normal older adults (age 74.1 ± 6.8 years, 59.7% female, 85.8% white) who underwent Aβ positron emission tomography (Aβ-PET) and who completed the Ohio State University Traumatic Brain Injury Identification questionnaire. We limited participants to those reporting injuries classified as mTBI. A subset (N = 30) underwent a second Aβ-PET scan (mean 2.7 years later). We examined the effect of remote mTBI on Aβ-PET burden, interactions between remote mTBI and age, sex, and APOE status, longitudinal Aβ accumulation, and the interaction between remote mTBI and Aβ burden on memory and executive functioning. Of 134 participants, 48 (36%) reported remote mTBI (0, N = 86; 1, N = 31, 2+, N = 17; mean 37 ± 23 years since last mTBI). Effect size estimates were small to negligible for the association of remote mTBI with Aβ burden (p = .94, η2 < 0.01), and for all interaction analyses. Longitudinally, we found a non-statistically significant association of those with remote mTBI (N = 11) having a faster rate of Aβ accumulation (B = 0.01, p = .08) than those without (N = 19). There was no significant interaction between remote mTBI and Aβ burden on cognition. In clinically normal older adults, history of mTBI is not associated with greater cortical Aβ burden and does not interact with Aβ burden to impact cognition. Longitudinal analyses suggest remote mTBI may be associated with more rapid cortical Aβ accumulation. This finding warrants further study in larger and more diverse samples with well-characterized lifelong head trauma exposure.

Epidemiology of Chronic Effects of Traumatic Brain Injury

Although many patients diagnosed with traumatic brain injury (TBI), particularly mild TBI, recover from their symptoms within a few weeks, a small but meaningful subset experience symptoms that persist for months or years after injury and significantly impact quality of life for the person and their family. Factors associated with an increased likelihood of negative TBI outcomes include not only characteristics of the injury and injury mechanism, but also the person’s age, pre-injury status, comorbid conditions, environment, and propensity for resilience. In this article, as part of the Brain Trauma Blueprint: TBI State of the Science framework, we examine the epidemiology of long-term outcomes of TBI, including incidence, prevalence, and risk factors. We identify the need for increased longitudinal, global, standardized, and validated assessments on incidence, recovery, and treatments, as well as standardized assessments of the influence of genetics, race, ethnicity, sex, and environment on TBI outcomes. By identifying how epidemiological factors contribute to TBI outcomes in different groups of persons and potentially impact differential disease progression, we can guide investigators and clinicians toward more-precise patient diagnosis, along with tailored management, and improve clinical trial designs, data evaluation, and patient selection criteria.

The Impact of Age and Severity on Dementia After Traumatic Brain Injury: A Comparison Study

BACKGROUND

Growing evidence associates traumatic brain injury (TBI) with increased risk of dementia, but few studies have evaluated associations in patients younger than 55 yr using non-TBI orthopedic trauma (NTOT) patients as controls to investigate the influence of age and TBI severity, and to identify predictors of dementia after trauma.

OBJECTIVE

To investigate the relationship between TBI and dementia in an institutional group.

METHODS

Retrospective cohort study (2000-2018) of TBI patients aged 45 to 100 yr vs NTOT controls. Primary outcome was dementia after TBI (followed ≤10 yr). Cox proportional hazards models were used to assess risk of dementia; logistic regression models assessed predictors of dementia.

RESULTS

Among 24 846 patients, TBI patients developed dementia (7.5% vs 4.6%) at a younger age (78.6 vs 82.7 yr) and demonstrated higher 10-yr mortality than controls (27% vs 14%; P < .001). Mild TBI patients had higher incidence of dementia (9%) than moderate/severe TBI (5.4%), with lower 10-yr mortality (20% vs 31%; P < .001). Risk of dementia was significant in all mild TBI age groups, even 45 to 54 yr (hazard ratio 4.1, 95% CI 2.7-7.8). A total of 10-yr cumulative incidence was higher in mild TBI (14.4%) than moderate/severe TBI (11.3%) and controls (6.8%) (P < .001). Predictors of dementia include TBI, sex, age, hypertension, hyperlipidemia, stroke, depression, anxiety, and Injury Severity Score.

CONCLUSION

Mild and moderate/severe TBI patients experienced higher incidence of dementia, even in the youngest group (45-54 yr old), than NTOT controls. All TBI patients, especially middle-aged adults with minor injury who are more likely to be overlooked, should be monitored for dementia.

A meta-analysis of cohort studies: Traumatic brain injury and risk of Alzheimer's Disease

Introduction

Recently, some epidemiological studies have reported that cognitive disorders in elderly people is accelerated with traumatic brain injury. But the causal relationship between traumatic brain injury and AD is still an area of controversy.

Aims

Our review was conducted to estimate the relation between traumatic brain injury and risk of AD.

Methods

All longitudinal population-based studies comparing incidence of AD between subjects with and without traumatic brain injury from their inception to September 2020 were searched in The Cochrane Library, PubMed, Medline, Embase, Web of Science without restriction of language. The meta-analysis was conducted using Stata software.

Results

A total of 17 studies involving 4289,548 individuals were included. After pooling these 17 studies, subjects with traumatic brain injury had significant higher incidence of AD than those without traumatic brain injury (RR: 1.17, 95% CI: 1.05–1.29). When considering the severity of traumatic brain injury, this elevated risk of AD was still significant comparing subjects with moderate and severe traumatic brain injury and those with no traumatic brain injury (RR: 1.30, 95% CI: 1.01–1.59).

Conclusion

Traumatic brain injury, especially moderate and severe traumatic brain injury may be associated with increased risk of AD.

Head Injury Exposure in Veterans Presenting to Memory Disorders Clinic: An Observational Study of Clinical Characteristics and Relationship of Event-Related Potentials and Imaging Markers

Objective: Traumatic brain injury (TBI) and repetitive head impacts (RHI) related to blasts or contact sports are commonly reported among military service members. However, the clinical implications of remote TBI and RHI in veterans remains a challenge when evaluating older veterans at risk of neurodegenerative conditions including Alzheimer's disease (AD) and Chronic Traumatic Encephalopathy (CTE). This study aimed to test the hypothesis that veterans in a memory disorders clinic with remote head injury would be more likely to have neurodegenerative clinical diagnoses, increased rates of amyloid PET positivity, higher prevalence of cavum septum pellucidi/vergae, and alterations in event-related potential (ERP) middle latency auditory evoked potentials (MLAEPs) and long latency ERP responses compared to those without head injuries. Methods: Older veterans aged 50-100 were recruited from a memory disorders clinic at VA Boston Healthcare system with a history of head injury (n = 72) and without head injury history (n = 52). Patients were classified as reporting prior head injury including TBI and/or RHI exposure based on self-report and chart review. Participants underwent MRI to determine presence/absence of cavum and an ERP auditory oddball protocol. Results: The head injury group was equally likely to have a positive amyloid PET compared to the non-head injury group. Additionally, the head injury group were less likely to have a diagnosis of a neurodegenerative condition than those without head injury. P200 target amplitude and MLAEP amplitudes for standard and target tones were decreased in the head injury group compared to the non-head injury group while P3b amplitude did not differ. Conclusions: Veterans with reported remote head injury evaluated in a memory disorders clinic were not more likely to have a neurodegenerative diagnosis or imaging markers of neurodegeneration than those without head injury. Decreased P200 target and MLAEP target and standard tone amplitudes in the head injury group may be relevant as potential diagnostic markers of remote head injury.

Helicopter emergency medical service dispatch in older trauma: time to reconsider the trigger?

BACKGROUND

Helicopter Emergency Medical Services (HEMS) respond to serious trauma and medical emergencies. Geographical disparity and the regionalisation of trauma systems can complicate accurate HEMS dispatch. We sought to evaluate HEMS dispatch sensitivity in older trauma patients by analysing critical care interventions and conveyance in a well-established trauma system.

METHODS

All trauma patients aged ≥65 years that were attended by the Air Ambulance Kent Surrey Sussex over a 6-year period from 1 July 2013 to 30 June 2019 were included. Patient characteristics, critical care interventions and hospital disposition were stratified by dispatch type (immediate, interrogate and crew request).

RESULTS

1321 trauma patients aged ≥65 were included. Median age was 75 years [IQR 69-89]. HEMS dispatch was by immediate (32.0%), interrogation (43.5%) and at the request of ambulance clinicians (24.5%). Older age was associated with a longer dispatch interval and was significantly longer in the crew request category (37 min [34-39]) compared to immediate dispatch (6 min [5-6] (p = .001). Dispatch by crew request was common in patients with falls < 2 m, whereas pedestrian road traffic collisions and falls > 2 m more often resulted in immediate dispatch (p = .001). Immediate dispatch to isolated head injured patients often resulted in pre-hospital emergency anaesthesia (PHEA) (39%). However, over a third of head injured patients attended after dispatch by crew request received PHEA (36%) and a large proportion were triaged to major trauma centres (69%).

CONCLUSIONS

Many patients who do not fulfil the criteria for immediate HEMS dispatch need advanced clinical interventions and subsequent tertiary level care at a major trauma centre. Further studies should evaluate if HEMS activation criteria, nuanced by age-dependant triggers for mechanism and physiological parameters, optimise dispatch sensitivity and HEMS utilisation.

Factors affecting functional outcomes of traumatic brain injury rehabilitation at a rehabilitation facility in Saudi Arabia

Objectives:

To identify the factors that affect disability after inpatient rehabilitation (IPR) in persons with traumatic brain injury (TBI).

Methods:

This retrospective study identified 140 patients aged ≥16 years who were admitted to the TBI rehabilitation unit at King Fahad Medical City, Riyadh, Kingdom of Saudi Arabia between 2015 and 2017. The collected data included demographic variables, TBI cause, coma duration, time from injury to IPR, LOS, and Functional Independence Measure (FIM) scores at IPR admission and discharge.

Results:

Majority of the patients were young males. The TBI was caused by motor vehicle accidents (MVA) in 95% of patients. The mean coma duration, time from injury to IPR admission, and LOS were 47±38, 264±357, and 75±52 days, respectively. The factors that were found to have an association with FIM change were time from injury to IPR admission (p=0.003, r=-0.250), admission FIM score (p=0.003, r=-0.253), and discharge FIM score (p<0.001, r=0.390). Employed patients had high FIM scores at admission (p=0.029, r=0.184) and discharge (p=0.003, r=0.252).

Conclusion:

Reduction in disability at discharge was positively associated with the severity of disability at admission and negatively with the time duration from injury to IPR admission, indicating a need to reduce time before admittance to an IPR setup. The high incidence of MVA causing TBI in a young male population strongly points to a need for appropriate measures of prevention.

The Delayed Neuropathological Consequences of Traumatic Brain Injury in a Community-Based Sample

The late neuropathological effects of traumatic brain injury have yet to be fully elucidated, particularly with respect to community-based cohorts. To contribute to this critical gap in knowledge, we designed a multimodal neuropathological study, integrating traditional and quantitative approaches to detect pathologic changes in 532 consecutive brain autopsies from participants in the Adult Changes in Thought (ACT) study. Diagnostic evaluation including assessment for chronic traumatic encephalopathy (CTE) and quantitative immunoassay-based methods were deployed to examine levels of pathological (hyperphosphorylated) tau (pTau) and amyloid (A) β in brains from ACT participants with (n = 107) and without (n = 425) history of remote TBI with loss of consciousness (w/LOC). Further neuropathological assessments included immunohistochemistry for α-synuclein and phospho-TDP-43 pathology and astro- (GFAP) and micro- (Iba1) gliosis, mass spectrometry analysis of free radical injury, and gene expression evaluation (RNA sequencing) in a smaller sub-cohort of matched samples (49 cases with TBI and 49 non-exposed matched controls). Out of 532 cases, only 3 (0.6%-none with TBI w/LOC history) showed evidence of the neuropathologic signature of chronic traumatic encephalopathy (CTE). Across the entire cohort, the levels of pTau and Aβ showed expected differences for brain region (higher levels in temporal cortex), neuropathological diagnosis (higher in participants with Alzheimer's disease), and APOE genotype (higher in participants with one or more APOE ε4 allele). However, no differences in PHF-tau or Aβ1-42 were identified by Histelide with respect to the history of TBI w/LOC. In a subset of TBI cases with more carefully matched control samples and more extensive analysis, those with TBI w/LOC history had higher levels of hippocampal pTau but no significant differences in Aβ, α-synuclein, pTDP-43, GFAP, Iba1, or free radical injury. RNA-sequencing also did not reveal significant gene expression associated with any measure of TBI exposure. Combined, these findings suggest long term neuropathological changes associated with TBI w/LOC may be subtle, involve non-traditional pathways of neurotoxicity and neurodegeneration, and/or differ from those in autopsy cohorts specifically selected for neurotrauma exposure.

Association of remote traumatic brain injury and military employment with late-life trajectories of depressive symptom severity

BACKGROUND

Traumatic brain injury (TBI) and military service are common lifetime exposures among current older adults that may affect late-life mental health. The objective of the present study was to evaluate the association between TBI with loss of consciousness (LOC) and military employment and late-life depressive symptom severity trajectory.

METHODS

1445 males and 2096 females adults at least 65 years old without dementia or recent TBI were enrolled and followed biennially for up to 10 years in the Adult Changes in Thought study from Kaiser Permanente Washington in Seattle, Washington.

RESULTS

Using group-based trajectory modeling, we documented four distinct depressive symptom severity trajectories that followed a similar course in males and females (Minimal, Decreasing, Increasing, and Persistent). In multinomial regression analyses, TBI with LOC in males was associated with greater likelihood of Persistent versus Minimal depressive symptom severity compared to individuals without TBI (OR = 1.51, 95% CI: 1.01, 2.27; p=0.046). Males reporting past military employment had greater likelihood of Decreasing versus Minimal depressive symptom severity compared to individuals without past military employment (OR = 1.54, 95% CI: 1.03, 2.31; p=0.035). There was no association between TBI or military employment and depression trajectories in females, and no evidence of effect modification by age or between exposures.

LIMITATIONS

Lifetime history of TBI was ascertained retrospectively and may be subject to recall bias. Also, past military employment does not presuppose combat exposure.

CONCLUSIONS

Remote TBI and past military employment are relevant to late-life trajectories of depressive symptom severity in dementia-free older males.

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.

Reinjury After Moderate to Severe TBI: Rates and Risk Factors in the NIDILRR Traumatic Brain Injury Model Systems

OBJECTIVES

To compare characteristics of those who do and do not sustain subsequent traumatic brain injuries (TBIs) following index TBI and to identify reinjury risk factors.

DESIGN

Secondary data analysis of an ongoing longitudinal cohort study.

SETTING

TBI Model Systems Centers.

PARTICIPANTS

In total, 11 353 individuals aged 16+ years.

MAIN OUTCOME MEASURES

Ohio State University TBI Identification Method.

RESULTS

In total, 7.9% of individuals reported sustaining a TBI post-index TBI. Twenty percent of reinjuries occurred within a year of the index TBI. Reinjury risk followed an approximate U-shaped distribution such that risk was higher in the first year, declined 2 to 10 years postinjury, and then increased after 10 years. A multivariable Weibull model identified predictors of reinjury: younger (<29 years) and middle-aged and older (50+ years) age at index TBI relative to middle age, pre-index TBI, pre-index alcohol and illicit drug use, incarceration history, and less severe index TBI.

CONCLUSIONS

A subset of individuals who receive inpatient rehabilitation for TBI are at an increased risk for reinjury, and an injury-prone phenotype may be characterized by engagement in risk behaviors. Factors associated with reinjury risk may differ for younger versus middle-aged and older adults. Findings underscore the need for empirically informed risk stratification models to identify TBI survivors at risk for reinjury.

Broader Insights into Understanding Tumor Necrosis Factor and Neurodegenerative Disease Pathogenesis Infer New Therapeutic Approaches

Proinflammatory cytokines such as tumor necrosis factor (TNF), with its now appreciated key roles in neurophysiology as well as neuropathophysiology, are sufficiently well-documented to be useful tools for enquiry into the natural history of neurodegenerative diseases. We review the broader literature on TNF to rationalize why abruptly-acquired neurodegenerative states do not exhibit the remorseless clinical progression seen in those states with gradual onsets. We propose that the three typically non-worsening neurodegenerative syndromes, post-stroke, post-traumatic brain injury (TBI), and post cardiac arrest, usually become and remain static because of excess cerebral TNF induced by the initial dramatic peak keeping microglia chronically activated through an autocrine loop of microglial activation through excess cerebral TNF. The existence of this autocrine loop rationalizes post-damage repair with perispinal etanercept and proposes a treatment for cerebral aspects of COVID-19 chronicity. Another insufficiently considered aspect of cerebral proinflammatory cytokines is the fitness of the endogenous cerebral anti-TNF system provided by norepinephrine (NE), generated and distributed throughout the brain from the locus coeruleus (LC). We propose that an intact LC, and therefore an intact NE-mediated endogenous anti-cerebral TNF system, plus the DAMP (damage or danger-associated molecular pattern) input having diminished, is what allows post-stroke, post-TBI, and post cardiac arrest patients a strong long-term survival advantage over Alzheimer's disease and Parkinson's disease sufferers. In contrast, Alzheimer's disease and Parkinson's disease patients remorselessly worsen, being handicapped by sustained, accumulating, DAMP and PAMP (pathogen-associated molecular patterns) input, as well as loss of the LC-origin, NE-mediated, endogenous anti-cerebral TNF system. Adrenergic receptor agonists may counter this.

What do we know about the risks of developing dementia after traumatic brain injury?

Traumatic brain injury (TBI) is a risk factor for the later development of dementia, but although the evidence dates back to the early 20^th century, the nature of any association and its mechanistic pathways remain unclear. There has been greater focus on this subject over recent years, in part because of increasing reports around sports related TBIs, especially in the USA. Differences in research methods and clinical sampling remain the primary reason for the variable findings, although there is clearly increased prevalence of neurodegenerative disorders in general. Duration of follow up, definition of both TBI and dementia, and differences in the extent to which other dementia risk factors are controlled, as well as concerns about medical record accuracy are all issues yet to be resolved in TBI research, as is an absence pathological evidence. In addition, TBI has been reported to initiate a cascade of pathological processes related to several neurodegenerative disorders, and as such, it is likely that the risks vary between individuals. Given the evidence that dementia risk may increase with injury severity and frequency, a detailed account of age and type of injury, as well as lifetime TBI exposure is essential to document in future studies, and further longitudinal research with biomarker assessments are needed.

Traumatic Brain Injury and Risk of Long-Term Brain Changes, Accumulation of Pathological Markers, and Developing Dementia: A Review

Traumatic brain injuries (TBI) have received widespread media attention in recent years as being a risk factor for the development of dementia and chronic traumatic encephalopathy (CTE). This has sparked fears about the potential long-term effects of TBI of any severity on cognitive aging, leading to a public health concern. This article reviews the evidence surrounding TBI as a risk factor for the later development of changes in brain structure and function, and an increased risk of neurodegenerative disorders. A number of studies have shown evidence of long-term brain changes and accumulation of pathological biomarkers (e.g., amyloid and tau proteins) related to a history of moderate-to-severe TBI, and research has also demonstrated that individuals with moderate-to-severe injuries have an increased risk of dementia. While milder injuries have been found to be associated with an increased risk for dementia in some recent studies, reports on long-term brain changes have been mixed and often are complicated by factors related to injury exposure (i.e., number of injuries) and severity/complications, psychiatric conditions, and opioid use disorder. CTE, although often described as a neurodegenerative disorder, remains a neuropathological condition that is poorly understood. Future research is needed to clarify the significance of CTE pathology and determine whether that can explain any clinical symptoms. Overall, it is clear that most individuals who sustain a TBI (particularly milder injuries) do not experience worse outcomes with aging, as the incidence for dementia is found to be less than 7% across the literature.

Association of traumatic brain injury with dementia and memory decline in older adults in the United States

INTRODUCTION

To examine associations of history of traumatic brain injuries (TBIs) with loss of consciousness (LOC) with dementia incidence and memory decline.

METHODS

We studied 2718 participants from the 1992 enrollment cohort of the Health and Retirement Study (HRS) aged 65 years or older in 2000. History of TBI with LOC was self-reported in 1992. Dementia was assessed using four algorithms established in HRS. Participants were followed from 2000 to 2014 with repeated measures of dementia and memory performance. Cox models and linear mixed-effects models were used.

RESULTS

In 1992, 11.9% of the participants reported a history of TBI with LOC. In fully adjusted models for all four algorithms, participants with a history of TBI with LOC had no statistically significant difference in dementia incidence nor in memory decline, compared to participants without TBI history.

DISCUSSION

Our study did not find evidence of a long-term association between history of TBI with LOC (of unknown frequency and severity) and dementia incidence or memory decline.

Microglial Depletion with CSF1R Inhibitor During Chronic Phase of Experimental Traumatic Brain Injury Reduces Neurodegeneration and Neurological Deficits

Chronic neuroinflammation with sustained microglial activation occurs following severe traumatic brain injury (TBI) and is believed to contribute to subsequent neurodegeneration and neurological deficits. Microglia, the primary innate immune cells in brain, are dependent on colony stimulating factor 1 receptor (CSF1R) signaling for their survival. In this preclinical study, we examined the effects of delayed depletion of chronically activated microglia on functional recovery and neurodegeneration up to 3 months postinjury. A CSF1R inhibitor, Plexxikon (PLX) 5622, was administered to adult male C57BL/6J mice at 1 month after controlled cortical impact to remove chronically activated microglia, and the inhibitor was withdrawn 1-week later to allow for microglial repopulation. Following TBI, the repopulated microglia displayed a ramified morphology similar to that of Sham uninjured mice, whereas microglia in vehicle-treated TBI mice showed the typical chronic posttraumatic hypertrophic morphology. PLX5622 treatment limited TBI-associated neuropathological changes at 3 months postinjury; these included a smaller cortical lesion, reduced hippocampal neuron cell death, and decreased NOX2- and NLRP3 inflammasome-associated neuroinflammation. Furthermore, delayed depletion of chronically activated microglia after TBI led to widespread changes in the cortical transcriptome and altered gene pathways involved in neuroinflammation, oxidative stress, and neuroplasticity. Using a variety of complementary neurobehavioral tests, PLX5622-treated TBI mice also had improved long-term motor and cognitive function recovery through 3 months postinjury. Together, these studies demonstrate that chronic phase removal of neurotoxic microglia after TBI using CSF1R inhibitors markedly reduce chronic neuroinflammation and associated neurodegeneration, as well as related motor and cognitive deficits.SIGNIFICANCE STATEMENT Traumatic brain injury (TBI) is a debilitating neurological disorder that can seriously impact the patient's quality of life. Microglial-mediated neuroinflammation is induced after severe TBI and contributes to neurological deficits and on-going neurodegenerative processes. Here, we investigated the effect of breaking the neurotoxic neuroinflammatory loop at 1-month after controlled cortical impact in mice by pharmacological removal of chronically activated microglia using a colony stimulating factor 1 receptor (CSF1R) inhibitor, Plexxikon 5622. Overall, we show that short-term elimination of microglia during the chronic phase of TBI followed by repopulation results in long-term improvements in neurological function, suppression of neuroinflammatory and oxidative stress pathways, and a reduction in persistent neurodegenerative processes. These studies are clinically relevant and support new concepts that the therapeutic window for TBI may be far longer than traditionally believed if chronic and evolving microglial-mediated neuroinflammation can be inhibited or regulated in a precise manner.

POINT/COUNTER-POINT-Links between traumatic brain injury and dementia remain poorly defined

There has been considerable public interest in the topic of traumatic brain injury (TBI) as a risk factor for development of late-life dementia. A review was performed on empirical studies examining the relationship between these two conditions. Although results from a number of studies clearly demonstrate that TBI is a positive risk factor for developing dementia, there are an equivalent number of studies that obtain inconclusive or negative findings. Inconsistencies across studies are often the result of methodological findings including the nature of the investigational design, choice of comparison groups, and criteria used to define cases. In many studies, the diagnosis of TBI is obtained retrospectively in a manner that is subject to bias. Accurate identification of dementia cases is often compromised by the use of inappropriately brief follow-up periods and variations in diagnostic methods. There remains no universally accepted neurobiological mechanism to explain the transition from acute TBI to the chronic effects of dementia. Studies of specialty populations, including athletes and military personnel are beset by secular and cohort effects, raising questions about the applicability of findings to the general population. No existing studies have been able to exclude the possible effects of confounding medical or lifestyle factors in facilitating the onset of dementia following TBI. Although the research findings suggest a general association between TBI and dementia, the specifics of the relationship remain poorly defined.

Associations of Race-Ethnicity and History of Traumatic Brain Injury With Age at Onset of Alzheimer's Disease

OBJECTIVE

This study examined whether a history of traumatic brain injury (TBI) is associated with age at onset of Alzheimer's disease (AD) in three racial-ethnic groups.

METHODS

Data from 7,577 non-Hispanic Caucasian, 792 African American, and 870 Hispanic participants with clinically diagnosed AD were obtained from the National Alzheimer's Coordinating Center. Participants were categorized by the presence or absence of self-reported remote history of TBI (>1 year before diagnosis of AD) with loss of consciousness (LOC) (TBI+) or no history of TBI with LOC (TBI-). Any group differences in education; sex; APOE ε4 alleles; family history of dementia; or history of depression, stroke, hypertension, hypercholesterolemia, and diabetes were included in analyses of covariance comparing clinician-estimated age at AD symptom onset for the TBI+ and TBI- groups.

RESULTS

AD onset occurred 2.3 years earlier for non-Hispanic Caucasians (F=30.49, df=1, 7,572, p<0.001) and 3.4 years earlier for African Americans (F=5.17, df=1, 772, p=0.023) in the TBI+ group. In the Hispanic cohort, females in the TBI+ group had AD onset 5.6 years earlier, compared with females in the TBI- group (F=6.96, df=1, 865, p=0.008); little difference in age at AD onset was observed for Hispanic males with and without a TBI history.

CONCLUSIONS

A history of TBI with LOC was associated with AD onset 2-3 years earlier in non-Hispanic Caucasians and African Americans and an onset nearly 6 years earlier in Hispanic females; no association was observed in Hispanic males. Further work in underserved populations is needed to understand possible underlying mechanisms for these differences.