Exploring the Evidence for Characterizing T.B.I Injury as a Chronic Condition - Examining Traumatic Brain Injury as a Chronic Condition

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National Academies of Sciences, Engineering, and Medicine; Health and Medicine Division; Board on Health Sciences Policy; Forum on Traumatic Brain Injury; Bowman K, Bologna A, Yost O, editors. Examining Traumatic Brain Injury as a Chronic Condition: Proceedings of a Workshop. Washington D.C: National Academies Press U.S; 2026 Jan 27.

2 Exploring the Evidence for Characterizing T.B.I Injury as a Chronic Condition

Key Points Highlighted by Individual Speakers

- Traumatic brain injury (T.B.I) can lead to long-term sequelae across physical, cognitive, emotional, and social domains, with outcomes that evolve over time rather than remaining static. These impacts may persist years after the initial injury and can significantly affect independence, employment, and social participation (Dams-O'Connor, Sander).

- T.B.I is linked to higher risks of mortality, disability, cognitive decline, dementia, epilepsy, stroke, falls, frailty, and psychiatric and medical comorbidities. The number and severity of T.B.I's compound these risks, underscoring the need for long-term monitoring and care (Sander, Schneider).

- A paradigm shift is needed that moves away from viewing T.B.I as an acute event. This includes improving T.B.I screening, adopting longitudinal care models, broadening inclusion in research and services, and using epidemiologic and other data to address knowledge gaps (Corrigan, Sander).

- Outcomes after T.B.I are shaped by multiple interconnected factors, including comorbidities, age, socioeconomic status, injury history, and access to care, requiring a multifaceted and person-centered approach to treatment and support (Sander).

- Research is needed to better understand such areas as comorbidity interactions, cognitive changes over time, sex differences in T.B.I injury and recovery, and developmental timing of injury (Corrigan, Sander, Schneider).

- T.B.I triggers long-term neuroinflammation and can hasten age-related neuropathology and cognitive impairment, with molecular evidence of neuroinflammation detected even decades postinjury (Loane).

- Moderate to severe T.B.I can initiate systemic inflammation that evolves from acute immunosuppression to chronic immune dysfunction, increasing susceptibility to infections and comorbidities. This underscores the need to treat T.B.I as a systemic condition, not solely a neurological one (Loane).

- Drugs targeting specific inflammatory pathways could help prevent or slow neurodegeneration after T.B.I. These findings expand the potential therapeutic window beyond the acute phase of injury (Loane).

- Biomarker-based approaches, such as the Rehabilomics model, which maps inflammatory biomarkers to functional outcomes, reveal how inflammatory load influences cognition, independence, and quality of life. This approach supports development of tailored and individualized treatments (Wagner).

- Developments in scalable biomarker technologies integrated with point-of-care diagnostics and telehealth may enable greater real-time monitoring and personalized treatment in community settings, to support long-term recovery (Wagner).

- Individuals with T.B.I are eight times more likely to develop major depression in the first year postinjury, with potentially long-lasting effects, even among those with no prior history of mental health issues. Depression is closely linked to other conditions including pain, cognitive dysfunction, and insomnia, and treating these can improve depressive symptoms (Bombardier).

- Post-traumatic epilepsy can pose a significant psychosocial burden on people who experience this condition after T.B.I. Its severity is linked to injury characteristics and age, and individuals with post-traumatic epilepsy face more complex care needs than those with either epilepsy or T.B.I alone (Pugh).

- Up to 25 to 30 percent of adults with persistent T.B.I symptoms at 1 year after T.B.I may have pituitary hormone deficiencies. Symptoms may be misattributed or dismissed, contributing to underdiagnosis of hypopituitarism. Proper endocrine evaluation is critical, as appropriate replacement can reverse symptoms due to hormone deficiencies, significantly improving cognition, mood, physical health, and quality of life (Wexler).

- T.B.I is a significant risk factor for such cardiovascular comorbidities as hypertension and coronary artery disease. Incidence is high even in the young T.B.I patients of the 18 to 40 years age group compared to an uninjured group, warranting awareness, screening, and strategies for long-term management (Izzy).

- T.B.I increases dementia risk by 71 percent and is associated with multiple and often co-occurring underlying neuropathologies including both Alzheimer's disease and non-Alzheimer's disease pathologies. Addressing modifiable T.B.I comorbidities may help prevent or delay cognitive decline, and adapting emerging dementia diagnostics to post-T.B.I contexts is urgently needed (Gardner).

- Comorbidities can emerge or persist years after T.B.I, and treatable conditions such as depression and pituitary hormone deficiencies can be overlooked because their symptoms resemble those of T.B.I. Longitudinal monitoring and personalized assessments, including biomarker tools, are key to improving diagnostic accuracy and care (Bombardier, Gardner, Izzy, Pugh, Wexler).

- Targeted interventions for T.B.I symptoms, even when initiated years after injury, can yield significant functional gains, particularly when designed to restore host function and applied in appropriately intensive care or rehabilitation settings (Ashley, Loane).

The first aim of the workshop was to describe the evidence for characterizing traumatic brain injury (T.B.I) as a chronic condition. Presentations and discussions over three sessions explored epidemiological data on the incidence and prevalence of long-term symptoms, the biological mechanisms underlying lasting health effects after T.B.I, and the symptoms and co-occurring health conditions associated with T.B.I as a chronic condition over the life course.

Epidemiology of T.B.I as A Chronic Condition

Kristen Dams-O'Connor, professor of rehabilitation and human performance and director of the Brain Injury Research Center of Mount Sinai, introduced and moderated the first of these sessions, which discussed data on the risks of increased mortality and long-term sequelae associated with T.B.I and what is known about biological and sociodemographic characteristics associated with an elevated risk of chronic T.B.I.

T.B.I is increasingly being recognized not merely as an acute event but as a chronic condition with wide-ranging and long-lasting implications across cognitive, emotional, and physical domains, as well as an array of associated comorbidities, Dams-O'Connor said. The session served to highlight emerging scientific evidence that supports this conceptualization, including how both injury-specific and individual characteristics contribute to the long-term trajectory of recovery or decline. For many individuals, symptoms may linger indefinitely, worsen with time, or even reemerge years after the original injury, underscoring a pattern that mirrors other chronic illnesses, she said.

The current health care model often falls short by declaring recovery at the point of stabilization or plateau, thereby ending care prematurely, Dams-O'Connor continued. However, many T.B.I survivors continue to improve, or can develop new or worsening conditions, well beyond those early stages. A growing body of research is shedding light on who benefits from continued rehabilitation and what types of care are most effective over time, she said. She highlighted the role of a proactive approach not only to enhance long-term outcomes but also to prevent avoidable setbacks by addressing symptoms before they escalate.

Dams-O'Connor concluded by underscoring the importance of epidemiological data in shaping care models in the near term, as prospective longitudinal studies that collect clinical and biological data continue to mature. Epidemiological data from representative samples play a crucial role in identifying patterns and risk factors, informing care strategies that are tailored to individual needs. As the field works to fill current knowledge gaps and overcome methodological limitations, there is renewed hope for optimizing quality of life for T.B.I survivors, she said. By better understanding who is at elevated risk and when to intervene, the health care system can develop more responsive lifelong care pathways that address the evolving realities of living with T.B.I.

Epidemiological Evidence of Long-Term T.B.I Sequelae

Andrea Schneider, assistant professor at the University of Pennsylvania Perelman School of Medicine, discussed the growing body of evidence that T.B.I is a multisystem condition associated with long-term risks including functional disability, cognitive decline, dementia, epilepsy, cardiovascular disease, frailty, and increased mortality—highlighting the need for longitudinal research and a comprehensive life-course approach to care and prevention.

T.B.I Prevalence and Mortality Trends

T.B.I poses a major public health challenge, with prevalence estimates in the United States ranging from 15 percent to 30 percent, Schneider began. A nationally representative study found that 15.7 percent of U.S. adults aged 40 and older reported a prior head injury with loss of consciousness, equating to nearly 23 million people (Schneider et al., 2018). Schneider emphasized that while T.B.I-related mortality was generally stable between 1999 and 2020, significant increases were observed among older adults, particularly those aged 75 and above (Shaik et al., 2024). Furthermore, individuals with a history of T.B.I had a twofold higher risk of long-term mortality over a median follow-up of 28 years compared to those without T.B.I, with mortality risk increasing in correlation with injury severity and frequency (Elser et al., 2023).

Functional Disability and Cognitive Decline

T.B.I has also been linked to persistent disability. Nearly 47 percent of individuals with a history of T.B.I reported at least one functional limitation, in contrast to 39 percent of those without such a history, with the most affected domains being mobility and work-related function (Schneider et al., 2021b). Using longitudinal data from the Atherosclerosis Risk in Communities (Aric) study, a community-based cohort of nearly 16,000 adults, Schneider and colleagues demonstrated that individuals with T.B.I experienced cognitive decline equivalent to being 7.4 years older at baseline compared to peers without T.B.I. Those with multiple T.B.I's experienced declines comparable to those nearly 10 years older at baseline, highlighting the cumulative toll of repeated injuries on cognitive health (Schneider et al., 2021a).

Risk of Dementia and Epilepsy

Beyond cognitive impairment, T.B.I significantly increases the risk for neurological disorders. Individuals with T.B.I had a 1.4-fold increased risk of developing dementia over a median follow-up of 25 years, with risk rising alongside the number of prior T.B.I's (Schneider et al., 2024b). Epilepsy is another critical sequela: individuals with T.B.I were found to be 1.9 times more likely to develop epilepsy over 11 years (Schneider et al., 2022). Notably, individuals with both post-traumatic epilepsy (P.T.E) and T.B.I had a threefold increased risk of developing dementia compared to those without either condition, underscoring the importance of examining the joint effect of comorbidities (Schneider et al., 2024a).

Cardiovascular and Physical Health Consequences

The implications of T.B.I extend into cardiovascular and physical health as well. Using an administrative dataset of over 600,000 veterans receiving health care in the Department of Veterans Affairs (V.A) system, T.B.I was associated with a 1.7-fold increased risk of stroke (ischemic or hemorrhagic) over 5 years, with elevated risk persisting for more than a decade (Figure 2 to 1; Schneider et al., 2023). Findings from Aric data supported this, showing a 1.3-fold higher risk of ischemic stroke in individuals with T.B.I, particularly among those with repeated or severe injuries (Elser et al., 2024). Additionally, individuals with T.B.I had a 1.7-fold increased risk of injurious falls requiring hospitalization over 23 years (Hunzinger et al., 2023) and were more likely to be prefrail or frail at baseline and to develop frailty over time (Hunzinger et al., 2024).

Image summary: Three forest plots showing that traumatic brain injury (TBI) increases the risk of any stroke, ischemic stroke, and hemorrhagic stroke in U.S. military veterans, with the highest risk associated with the most severe injury categories.

Figure 2 to 1

T.B.I is associated with 1.7 times the risk of any stroke (ischemic or hemorrhagic; Figure A) in U.S. military veterans over a median of 5 years, along with elevated risks for ischemic stroke (Figure B) and for hemorrhagic stroke (Figure C) over time. Note: (more...)

Research Gaps

Epidemiological data support the recognition of T.B.I as a chronic condition because of its wide-ranging and long-term sequelae, Schneider summarized. However, she noted that most studies focus on T.B.I as an isolated risk factor. She advocated for future research to address how T.B.I interacts with comorbid conditions, such as epilepsy, vascular disease, and frailty, and how both preinjury and postinjury factors influence outcomes across the life course. She also emphasized the need to identify high-risk subpopulations by examining medical comorbidities and social and environmental determinants of health and to target modifiable risk factors such as hypertension, diabetes, and smoking for prevention and intervention.

Using Longitudinal Data and Methodological Considerations

To advance T.B.I research, Schneider recommended using large-scale longitudinal datasets such as Aric for deeper insights. She acknowledged that while cost-effective, this approach entails navigating methodological challenges, including missing data, repeated measures, and study attrition. Nonetheless, such datasets enable researchers to evaluate T.B.I as a chronic, multisystem condition and to explore its cascading effects on cognition, physical health, and comorbidity-driven risks. Schneider concluded that a comprehensive, life-course approach—incorporating medical, social, and environmental dimensions—is essential to improving outcomes and care strategies for individuals with T.B.I.

Evidence from the T.B.I Model Systems National Database

Angelle Sander, professor in the Department of Physical Medicine and Rehabilitation at Baylor College of Medicine and director of T.I.R.R Memorial Hermann's Brain Injury Research Center, presented findings from the Traumatic Brain Injury Model Systems (T.B.I.M.S) National Database, a 35-year longitudinal study tracking individuals with moderate to severe T.B.I who received Level 1 trauma care and specialized rehabilitation. This national dataset provides detailed insights into long-term outcomes across physical, cognitive, social, and emotional domains (Dams-O'Connor et al., 2023b; see Box 2 to 1). T.B.I.M.S data confirm that individuals with T.B.I frequently experience persistent or evolving impairments even decades postinjury. Functional trajectories are dynamic, and patients may show recovery followed by decline, she said, emphasizing that early improvement does not guarantee long-term stability.

Box 2 to 1

Factors Affecting Outcomes in Chronic T.B.I.

Functional and Cognitive Outcomes Over Time

Functional change after T.B.I is more common than stability, Sander highlighted. A subset of T.B.I survivors showed improvement in functioning up to 10 years postinjury, with the most improvement seen early after injury. More than half of the individuals who survived their injuries were moderately to severely disabled at 5 years postinjury (Corrigan et al., 2014), and decline was common 5 to 10 years postinjury (Pretz and Dams-O'Connor, 2013). Physical improvements typically plateau earlier, whereas cognitive improvements can continue into the 5-year mark. Decline early postinjury is often linked to psychiatric conditions and poorer initial health, while later decline correlates with chronic medical issues (Kumar et al., 2020; Malec et al., 2019). Encouragingly, even individuals initially unable to follow commands often achieve self-care independence by year 10 (Hammond et al., 2019; Whyte et al., 2013), though many still function below normative cognitive levels, with 22 to 50 percent scoring below the third percentile at 5 years (Dams-O'Connor et al., 2018).

Comorbidities, Mental Health, and Risk of Reinjury

Sander highlighted that at least half of individuals with T.B.I are rehospitalized within 5 years, and 8 percent suffer another T.B.I, mostly within the first year (Corrigan et al., 2014). Comorbid conditions such as hypertension, respiratory issues, diabetes, and seizures are prevalent throughout recovery. Mental health is a critical concern: 25 percent of survivors meet criteria for major depressive disorder even two decades later, and within 5 years, 3 percent attempt suicide and an additional 8 percent report suicidal ideation (Dams-O'Connor et al., 2023b). These data underscore the enduring psychiatric burden of T.B.I and the need for sustained behavioral health interventions, she said.

Social, Vocational, and Substance Use Challenges

Participation in work, education, and community life is often affected after T.B.I. Employment rates hover between 53 and 60 percent through year 5, and gains in productive activity from years 2 to 5 often reverse by year 10 (Dams-O'Connor et al., 2023b). Between 36 and 41 percent report dissatisfaction with life, a figure that remains stable over time (Dams-O'Connor et al., 2023b). Substance use, particularly alcohol and illicit drugs, resurfaces postinjury as individuals regain mobility and community access, with 17 percent reporting problem alcohol use and 12 percent illicit drug use at year 5 (Dams-O'Connor et al., 2023b). These findings highlight the complex reentry challenges T.B.I survivors face, especially when underlying substance use histories are involved.

Additional Considerations

Sander emphasized that the risk of better or worse T.B.I outcomes differs across demographic and psychosocial lines. For example, individuals at elevated risk for chronic poor outcomes include older adults, those with early disability, and individuals with substance use histories. Young adults with functional independence may paradoxically be more vulnerable to risky behaviors, reinjury, and premature mortality, she noted.

Other influencing factors include coexisting health conditions, fitness levels, access to care, and social support. Given the interplay of these diverse factors, Sander called for a holistic bio-psychosocial-ecological approach to T.B.I management (Dams-O'Connor et al., 2023b; nasem, 2022).

Gaps in Rehabilitation Access and the Need for Broader Research

Despite the value of T.B.I.M.S data, fewer than 15 percent of individuals with moderate to severe T.B.I in the United States receive inpatient rehabilitation, and many do not receive Level 1 trauma care, she said. Sander pointed to the need for systematic, community-based studies on those outside the specialized care system, as their outcomes after T.B.I may be worse or more variable. Understanding how different outpatient or postacute services affect recovery could inform equitable, evidence-based care strategies, she emphasized. Ultimately, recognizing T.B.I as a chronic condition and expanding research beyond specialized cohorts will be essential to better address the long-term needs of all individuals affected by brain injury, she added.

Discussion

During discussion, Dams-O'Connor, Schneider, and Sander were joined by John Corrigan from the Ohio State University. The panel explored research gaps and considerations to gain a more comprehensive understanding of T.B.I as a chronic condition and develop an evidence-based approach to addressing it.

A Need for Life-Course and Preinjury Data in T.B.I Research

A point emphasized by all four panel members was the need for a life-course approach to understanding T.B.I. Schneider highlighted the importance of collecting robust preinjury data to assess how existing comorbidities influence recovery. Corrigan echoed this by advocating for longitudinal population-based studies, such as the Adolescent Brain Cognitive Development A.B.C.D study of youth aged 10 to 20 years and the Aric cohort, which can track developmental and aging-related changes over time. Research has shown that brain injuries sustained at different developmental stages, particularly early childhood or adolescence, may have distinct effects (Sariaslan et al., 2016). Moreover, T.B.I in older adults may serve as a sentinel event, often leading to loss of independence. The panelists noted the importance of longitudinal studies that follow individuals before and after injury to understand differences among individuals and corresponding effects on the injury over time, illuminating the full complexity of T.B.I as a chronic condition.

Methodological Challenges and Representative Sampling

Panelists discussed the issue of representativeness in T.B.I studies, with Corrigan noting the underrepresentation of women in T.B.I research as an important issue. Odette Harris, Stanford University and V.A Palo Alto Health Care System, Schneider, and Corrigan described a need for adequately powered studies to explore sex-related differences in outcomes after T.B.I. Limited studies exploring sex differences in T.B.I indicate that these differences can be significant, said Harris. Sex differences are observed with other chronic diseases, and T.B.I is not likely to be immune from these differences, Harris said. Many studies also exclude people who never sought care or received a diagnosis, said Dams-O'Connor, thereby introducing selection bias and systematically excluding those who may be at greatest risk for poor outcomes. The panelists called for greater community-based research and enhanced recruitment strategies that capture the populations not well reflected in current clinical datasets.

Self-Report and Standardization Efforts

Because many individuals with T.B.I never receive formal medical care, self-report remains essential, the panelists said. Sander noted findings from studies in which individuals with severe T.B.I's, including those with craniotomy scars, were unaware they had sustained a brain injury owing in part to a lack of postacute care and education. Schneider and Corrigan emphasized the development and validation of retrospective self-report tools and the importance of public education to improve self-recognition of T.B.I symptoms. Corrigan also highlighted the importance of developing agreed upon case definitions and classification standards, particularly for effective medical record abstraction.

Improved T.B.I ascertainment algorithms for use in medical records could increase granularity of data on those with T.B.I, Dams-O'Connor agreed, given that self-report data on care received often lack the level of detail included in medical records. While prospectively gathered data are ideal, the four panelists identified retrospective self-report as a legitimate and necessary method, especially when combined with other data sources such as hospital records, Medicare data, and existing longitudinal studies like Aric and the All of Us research program.

Using and Harmonizing Existing Datasets and Enhancing International Collaboration

Panelists emphasized the cost and time involved in launching new prospective studies and encouraged using existing ones. Schneider explained that studies such as Aric and All of Us, which already collect medical and self-report data, can be enhanced with standardized T.B.I screening instruments. Corrigan added that harmonizing T.B.I definitions and measurement across studies would improve comparability.

International collaborations, particularly with countries that have national health registries such as those in Scandinavia and New Zealand, were noted as promising opportunities. Corrigan and Schneider highlighted the value of these registries, which can link T.B.I data with outcomes such as employment, independence, and criminal history, although they noted that registry data typically do not include individuals who never sought care. Studies from the Centers for Disease Control and Prevention suggest that fewer than 5 percent of adult T.B.I's are treated in emergency departments, highlighting the limitations of relying solely on medical records, they said. Dams-O'Connor reaffirmed the need for a complementary mix of medical, self-report, and community-sourced data for a more accurate and inclusive understanding of T.B.I. Schneider also emphasized that low- and middle-income countries are largely absent from global T.B.I research. Panelists supported current efforts to urge the World Health Assembly to recognize T.B.I as a chronic and notifiable condition, to encourage broader data collection beyond countries with national registries.

Mechanisms of Injury and Cumulative Effects

The conversation broadened to include the need for more precise characterization of injury mechanisms. Corrigan emphasized that T.B.I is often not a single event but rather a cumulative series of exposures that occur across the life span. Military veterans, for instance, may experience simultaneous blast and blunt-force injuries.

Dams-O'Connor pointed out that different injury mechanisms, such as hypoxic injury caused by strangulation in intimate partner violence or repetitive concussions in sports, may have different long-term outcomes (Dams-O'Connor et al., 2023a). Understanding how biomechanics and injury characteristics influence long-term symptoms requires refined measurement and comprehensive injury profiles. Corrigan highlighted the effort through the National Institute of Neurological Disorders and Stroke to develop the new Clinical, Biomarker, Imaging, plus Modifier C.B.I-M approach to classifying T.B.I as a promising framework for capturing injury characteristics and modifiable risk factors (Manely et al., 2025).

Embracing Complexity and Future Research Directions

The session concluded with panelists emphasizing the importance of T.B.I research moving beyond overly simplistic models. Dams-O'Connor warned that focusing solely on “index injuries” (e.g., the initial brain injury that takes place in a given context) neglects the complexity of lifetime exposures. Schneider and Sander reiterated the importance of accounting for social and environmental determinants, comorbidities, and functional diversity in outcomes. For example, Corrigan and Dams-O'Connor emphasized the need for safe and effective screening for T.B.I in domestic violence shelters, while cautioning against the potential misuse of such data in legal contexts such as child custody disputes.

Corrigan called for broader use of the C.B.I-M framework and emphasized the need to understand injury context, timing, and cumulative burden. Collectively, the panel called for multidisciplinary, longitudinal research that reflects the multifactorial reality of living with T.B.I. Only by embracing this complexity can researchers, clinicians, and policy makers develop interventions that meaningfully improve long-term outcomes for people with T.B.I, Dams-O'Connor said.

neuropathophysiological Mechanisms Underlying T.B.I as A Chronic Condition

Amy Wagner, professor and vice chair in the Department of Physical Medicine and Rehabilitation at the University of Pittsburgh, introduced and moderated the next session, which explored the biological basis for chronic T.B.I and identified research gaps and barriers to advancing understanding of lasting health effects. This session and the following session on health outcomes and comorbidities included clinical and technical discussions of changes in the brain and immune system after T.B.I. As discussed by the speakers, research shows that T.B.I can accelerate brain aging, increase risk for neurodegenerative diseases such as Alzheimer's disease, and contribute to concerns such as depression, epilepsy, and chronic pain. Speakers described how an important driver of long-term effects after T.B.I is ongoing brain inflammation and disrupted communication between brain and body systems, which can leave people more vulnerable to infections and other health problems even years after injury.

Studies suggest that targeting inflammation, including from brain immune cells called microglia, may improve recovery even long after the initial injury. Session speakers also emphasized that T.B.I treatment, rehabilitation, and monitoring need to be tailored to the person's symptoms and stages of recovery.

T.B.I as a Chronic Neurological Condition

David Loane, neuroimmunologist and associate professor at Trinity College Dublin and adjunct associate professor at the University of Maryland School of Medicine, Baltimore, provided an overview of the chronic neuropathology of T.B.I, the contributions of chronic inflammation to neuropathology, the communication between central nervous system and peripheral systems in the context of systemic inflammation, associations between T.B.I and changes in the host immune response, and the risk those immune response changes pose in terms of secondary complications and mortality. Loane emphasized the complex and chronic nature of T.B.I, underscoring that both repetitive mild T.B.I's and single severe T.B.I's can lead to neurodegenerative diseases such as Alzheimer's disease and chronic traumatic encephalopathy C.T.E. These injuries are associated with long-term outcomes including hippocampal atrophy (a region of the brain associated with memory and cognitive function), executive dysfunction, psychiatric symptoms (e.g., depression, anxiety, aggression), post-traumatic epilepsy, and chronic pain. These effects highlight the enduring nature of T.B.I and challenge the outdated view that it is a short-term or static condition, he said.

Accelerated Brain Aging and Cognitive Impairment

Loane discussed evidence for the hypothesis that T.B.I accelerates brain aging. Using the Alzheimer's Disease Neuroimaging Initiative A.D.N.I database and machine learning, researchers demonstrated that T.B.I patients had a predicted brain age 4.66 years (gray matter) to 5.97 years (white matter) older than their chronological age (Cole et al., 2015). This accelerated aging was predictive of cognitive impairment and suggests that T.B.I pushes individuals closer to the threshold for age-related neurodegeneration (Smith et al., 2013). The work supports the notion that T.B.I disrupts the natural aging trajectory of the brain.

Neuropathological Mechanisms of Chronic T.B.I

Loane provided a detailed overview of neuropathological features linked with chronic T.B.I. These include amyloid beta accumulation, tau tangles, axonal degeneration, T.D.P-43 aggregation, and cerebrovascular pathology (Dams-O'Connor et al., 2023b; Emrani et al., 2025; Sandsmark et al., 2019). These changes are highly heterogeneous, reflecting differences in injury severity and mechanism. For instance, repetitive mild T.B.I may preferentially result in sulcal tau pathology and frontotemporal involvement, while severe T.B.I may involve diffuse axonal injury and white matter loss.

The Role of Chronic Neuroinflammation

Central to the chronic effects of T.B.I is sustained neuroinflammation. Loane highlighted microglia and astrocytes—the brain's innate immune cells—as key players. Chronic microglial activation persists postinjury and contributes to neurodegeneration, he said (Loane et al., 2014). Positron emission tomography imaging has shown long-term thalamic inflammation in T.B.I survivors 17 years postinjury (Ramlackhansingh et al., 2011), with evidence of hippocampal sclerosis and white matter degeneration (Johnson et al., 2013). Aging compounds this issue through “inflammaging,” a state of heightened immune responsiveness and cellular senescence (Scheiblich et al., 2020).

Microglia as Therapeutic Targets

Loane shared data from rodent models showing that targeted removal of chronically activated microglia using a colony-stimulating factor 1 receptor C.S.F.1.R inhibitor led to improved motor and cognitive outcomes, and arrested chronic lesion development (Henry et al., 2020). Microglial depletion suppressed the expression of genes associated with Alzheimer's-like neurodegeneration. These findings indicate that therapeutic interventions targeting microglial-mediated inflammation in the chronic postinjury period may restore brain function and halt further degeneration, he said, thereby expanding the window for effective treatment beyond the acute phase.

T.B.I as a Systemic Disorder

T.B.I affects not just the brain but also the peripheral immune system, Loane said, emphasizing the complex bidirectional communication between the brain and organs such as the lungs, liver, gut, and bone marrow. After a T.B.I, systemic immune responses are often triggered through the autonomic nervous system, the hypothalamic-pituitary-adrenal axis, and peripheral organ interactions, resulting in acute immunosuppression and, over time, chronic immune dysregulation (Meisel et al., 2005). In both clinical and animal studies, this dysregulation affects immune cell function, including phagocytosis and inflammatory responses, and can make the immune system less capable of fighting off subsequent infections or inflammatory conditions (Hanscom et al., 2021; Ritzel et al., 2018).

Vulnerability to Secondary Infections

Data indicate that both mild and more severe T.B.I's cause lasting vulnerabilities in immune function, Loane said, creating vulnerability to secondary complications such as infections during the chronic phase of recovery. Loane highlighted the increased susceptibility of T.B.I patients to infections, especially pneumonia, which is a leading cause of mortality. Rodent models showed that T.B.I suppresses immune cell function in the lungs, impairing the response to pathogens like Streptococcus pneumoniae (Doran et al., 2020). Infected T.B.I rodents exhibited higher mortality, increased brain inflammation, and reduced cytokine responses, such as interleukin-1 I.L-1. This vulnerability persisted even 60 days postinjury, suggesting that T.B.I leads to chronic immune dysfunction and hampers recovery from common infections long after the initial trauma.

Exacerbated Effects from Systemic Inflammation

In models where rodents were exposed to gastrointestinal inflammation via chemical colitis post-T.B.I, Loane shared data showing worsened motor outcomes and reactivation of autonomic dysregulation (Hanscom et al., 2021). Even mild T.B.I led to systemic immune impairment when challenged with secondary insults. Findings suggest that T.B.I induces a long-term shift in the host immune environment—first toward immunosuppression and later toward hyperinflammation. This evidence underscores the critical importance of understanding how systemic inflammation interacts with and exacerbates chronic brain injury, especially when patients face new health challenges months or years after their initial T.B.I.

Implications for Rehabilitation and Therapy

The chronic immune dysregulation observed in T.B.I creates opportunities for late-stage interventions, Loane continued. He emphasized the need for therapies that restore immune balance and mitigate neuroinflammation, such as agents targeting N.O.X.2 or N.L.R.P.3 inflammasomes. This perspective reframes T.B.I management to include the long-term biological impact of brain injury, where systemic inflammation is both a consequence and a contributor to ongoing neurological damage. Rehabilitation strategies should therefore address both neural and immune recovery, he emphasized.

Reframing T.B.I as a Chronic Disease

Loane concluded that T.B.I should be understood as a chronic disease with both central and systemic effects, where neuroinflammation and impaired immune responses play a critical role in shaping long-term health outcomes. Chronic pathology including brain atrophy, impaired host immunity, and susceptibility to secondary infections can profoundly affect long-term health outcomes, and research focused on the integrated pathobiology of T.B.I is needed to improve patient care, he said. He argued that advancing an understanding of the brain–immune system interplay could reveal key intervention points to improve recovery and reduce vulnerability to secondary complications across the life span. He also emphasized the usefulness of targeted interventions for T.B.I symptoms even if initiated well after the initial injury, particularly when designed to restore host function. Loane emphasized that rehabilitation and pharmacologic therapies should be developed to modify underlying mechanisms of dysfunction, highlighting the importance of timing and personalized treatment during the chronic phase of recovery.

Chronic T.B.I-Associated Pathology in the Context of Health, Chronic Conditions, and Function

Wagner echoed the need to consider T.B.I as a systemic condition, highlighting the importance of understanding the long-term effects of T.B.I on multiple body systems and the value of integrating biomarkers into this effort. She introduced her Rehabilomics Research model (Wagner, 2010), which aligns with calls for a broader, more holistic understanding of health, rooted in functional capacity rather than merely the absence of disease.

Using the World Health Organization's International Classification of Functioning, Disability and Health W.H.O, 2001) as a conceptual anchor, Wagner described how biomarkers can help identify the physiological underpinnings of functional deficits following T.B.I. Function, she argued, is a key indicator of health in chronic conditions like T.B.I, and understanding it requires analyzing how biological and environmental factors interact over time. She gave the example of cognitive impairment, one of the most debilitating outcomes after T.B.I, and described how her team developed an inflammatory load score that correlates early inflammatory markers with neuropsychological test results at 6 and 12 months postinjury (Milleville et al., 2020). This inflammatory load score not only predicted cognitive performance but was also associated with everyday functional outcomes like independence and quality of life, Wagner said.

She further highlighted how biomarkers can be used to better understand outcomes in T.B.I populations. Her team is mapping relationships among inflammatory and autoimmune markers, neuronal damage indicators such as the biomarker neurofilament light (NfL), and cognitive outcomes at 6 months postinjury. The analysis reveals connections among autoantibodies, inflammation, and cognitive impairment that form a complex biological network affecting recovery and help to identify potential therapeutic targets. This integrative approach is being extended to study active drivers of secondary conditions like microglial health, autophagy, and cellular senescence in collaboration with other researchers, she said.

Looking ahead, Wagner proposed that biomarker technologies could become scalable tools for monitoring chronic T.B.I in community settings. Coupled with telehealth platforms and point-of-care diagnostics, these tools could help track biological dysfunction in real time and offer personalized treatment recommendations. She concluded by suggesting that such innovations hold promise not just for research but for improving long-term recovery and daily life for individuals living with chronic effects of T.B.I.

Panel Discussion

Insights from Preclinical T.B.I Research

Wagner opened the discussion by asking about the limitations of rodent models in studying chronic T.B.I, specifically the challenge of translating rodent life spans to human conditions. Loane acknowledged these limitations but argued that rodent models offer unique opportunities to investigate genetic and inflammatory mechanisms over time that cannot be explored in humans. He emphasized the advantages of knowing both the timing of induced injury and the assessment window in experimental systems. He also advocated for integrating established clinical biomarkers, such as NfL and immune-related markers, into preclinical studies. This integration would allow researchers to better align rodent outcomes with human pathologies, he said, enhancing translational relevance.

Chronic Immune Dysfunction and Comorbidities

Wagner shifted the focus to chronic immune dysfunction and its role in secondary conditions such as epilepsy, depression, and fatigue that can arise months or years post-T.B.I. Loane highlighted interleukin-1 I.L-1 as a central immune mediator linking astrocytic and microglial activation to altered brain wiring, particularly in post-traumatic epilepsy. While complex conditions like frailty may be harder to model in rodents, he said, the use of biomarkers through blood assays or molecular imaging can help to identify overlapping mechanisms across comorbidities. This approach could help identify targets for individuals with treatment-resistant epilepsy and support the development of translational interventions, he suggested.

Cellular Aging, Senescence, and Treatment Targets

Wagner asked about cellular aging and senescence in older adults with T.B.I. Loane critiqued the blunt nature of steroid treatments that indiscriminately suppress immune function, arguing instead for more precise, mechanism-based drugs that modulate metabolism, cytokine signaling, and cell-specific pathways. Loane also highlighted the regenerative role of anti-inflammatory cytokines such as I.L-10, brain-derived neurotrophic factor, and nerve growth factor in promoting neural repair. He emphasized the importance of administering treatments at the correct time, saying that while microglia and astrocytes serve beneficial roles in the acute phase by clearing debris, their chronic activation can lead to neurodegeneration if left unchecked.

Timing and Tailored Interventions

Expanding on the role of timing, Loane suggested that different phases of T.B.I recovery might require different therapeutic strategies. For example, early postinjury interventions could focus on the modulation of autophagy to support cellular cleanup, while later stages might benefit from rehabilitation and exercise. Preclinical models allow for the testing of such sequenced interventions, he noted, especially when paired with pharmacodynamic biomarkers that track changes in neurodegeneration and inflammation. Loane challenged the idea there is only a narrow treatment window postinjury, emphasizing that T.B.I can be addressed as a lifelong condition with opportunities for intervention throughout the chronic phase.

Translation of Preclinical Research to Human Therapies

Throughout the discussion, Loane and Wagner emphasized the need to operationalize these preclinical insights into human clinical trials and to develop personalized, phase-specific interventions grounded in mechanistic understanding and supported by translational biomarkers. The use of biomarkers to bridge preclinical and clinical research could facilitate drug repurposing and personalized therapies, Loane suggested. Wagner added that behavioral models in rodents, when aligned with the inflammatory hypothesis of depression, could provide translational potential for treating neuropsychiatric sequelae of T.B.I. The dialogue highlighted how rodent models, when used thoughtfully and with clinically relevant markers, can inform the design of therapeutic interventions that address the full arc of T.B.I injury, recovery, and comorbidity.

Evidence on Health Outcomes and comorbidities

The third session explored outcomes and comorbidities linked to T.B.I, focusing on depression, post-traumatic epilepsy, endocrine dysfunction, cardiovascular disease, and dementia. The session was introduced and moderated by Jeanne Hoffman, a rehabilitation psychologist and professor in the Department of Rehabilitation Medicine at the University of Washington School of Medicine.

Hoffman highlighted the range and complexity of the long-term effects of T.B.I, noting that although the session could not cover every symptom, the five areas chosen illustrate the breadth of medical and psychological challenges that individuals with chronic T.B.I may face. These conditions can overlap and have a compounded effect on a person's daily function and quality of life, she added. Recognizing that these conditions influence long-term function and quality of life and identifying and addressing knowledge gaps in understanding how these conditions develop and interact over time will be key to improving treatment, prevention, and management of post-T.B.I outcomes, she said.

Before moving to the panel, Hoffman welcomed insights from several people experiencing long-term effects from T.B.I (Box 2 to 2).

Box 2 to 2

Perspectives of Individuals Living with Chronic T.B.I Symptoms.

Depression and T.B.I

Charles Bombardier, clinical psychologist and professor at the University of Washington, outlined the associations between T.B.I and long-term increased risk of depression and associated mental health conditions. A study found that 53 percent of 559 participants experienced a period of major depression during the 1 year period following hospitalization with T.B.I, constituting a rate eight times higher than that of the general population (Bombardier et al., 2010). Both T.B.I and individual history of depression drive this rate, he said, highlighting that 43 percent of the study sample reported depression diagnosis and/or treatment prior to T.B.I. Whereas 41 percent of individuals with no history of depression experienced an episode of depression during the first year after T.B.I, this figure rose to 69 percent for individuals with a prior history of depression and 73 percent for individuals experiencing depression at the time of injury. These findings indicate the importance of assessing T.B.I patient psychiatric history and screening for depression, Bombardier emphasized.

Bombardier highlighted research from Alway and colleagues that tracked 160 individuals with T.B.I and conducted diagnostic assessments of psychiatric disorders for 5 years postinjury (Alway et al., 2016). People with T.B.I are at elevated risk for a variety of neuropsychiatric conditions with rates gradually declining over time (see Figure 2 to 2 from Howlett et al., 2022, developed using data from Alway et al., 2016). Bombardier particularly noted that rates of mood disorders ranged from approximately 40 percent 1 year postinjury to 30 percent over the 5-year period, indicating a sustained effect of T.B.I on depression, he said.

Image summary: Line graph showing a general decline in the prevalence of psychiatric disorders over five years post-TBI, with mood and anxiety disorders remaining the most common conditions.

Figure 2 to 2

Prevalence of psychiatric disorders during the first 5 years after T.B.I. Note: The prevalence of mood, anxiety, and substance use disorders S.U.D's was assessed over 5 years of follow-up in a study of people who experienced moderate to severe T.B.I, indicating (more...)

Delving into the risk of depression after T.B.I, he reported that a study tracking patient data on over 4,000 individuals with T.B.I for 10 years postinjury found higher rates of depression compared to a similar sample with no T.B.I (Izzy et al., 2022). Emphasizing that this study excluded participants with a prior history of depression or T.B.I, Bombardier underscored that approximately 20 percent of individuals with mild T.B.I and 15 percent of individuals with moderate to severe T.B.I experienced depression compared to 5 percent of people with no history of T.B.I. Moreover, a long-term study of U.S. veterans demonstrated that risk of depression remains elevated for 50 years after T.B.I (Holsinger et al., 2002). The study compared a half century of records for approximately 1,000 World War 2 veterans hospitalized for nonpenetrating brain injuries and 1,000 veterans hospitalized for nonhead injuries. After controlling for demographic and health factors, researchers found that 18.5 percent of veterans with head injury demonstrated a lifetime history of major depression, compared to 13.4 percent of veterans with no head injury. The rate of current major depression at 50 years postinjury was 11.2 percent for veterans with head injury and 8.5 for those with no head injury. Bombardier emphasized that the increased risk of depression in individuals with T.B.I lasts a lifetime.

Risk of depression carries risk for associated conditions, Bombardier explained. For example, evidence indicates that depression can negatively affect cognitive impairment, insomnia, chronic pain, and functioning in social, recreational, and work settings (Andelic et al., 2018; Del Pozzo et al., 2024; Fann et al., 1995; Gomez-Hernandez et al., 1997; Hoge et al., 2008; Izzy et al., 2022; Kishi et al., 2001; Kumar et al., 2018; Rao et al., 2014; Rapoport et al., 2005; Satz et al., 1998; Teasdale and Engberg, 2001; Uiterwijk et al., 2022; Wickwire et al., 2023). Understanding relationships among conditions associated with depression offers new approaches for treating depression in individuals with T.B.I, he suggested. For example, a study of collaborative care treatment for chronic pain in people with T.B.I revealed improvements in both chronic pain and depression (Hoffman et al., 2024). Interventions to improve psychosocial, recreation, and work functioning also improved symptoms of depression (Bombardier et al., 2009). He concluded that treating conditions that contribute to depression could be an effective approach to improving depression in individuals with T.B.I.

Post-Traumatic Epilepsy

Mary Jo Pugh, professor of internal medicine and population health at the University of Utah, discussed the prevalence, complex comorbidity, and challenges associated with post-traumatic epilepsy (P.T.E). Defined as a recurrent seizure disorder occurring after T.B.I, P.T.E accounts for approximately 20 percent of symptomatic cases of epilepsy (Yu et al., 2021). Research indicates that the prevalence of epilepsy is higher in both civilian and military populations with T.B.I than in the general population. However, while estimates of P.T.E in civilians range from 2 to 20 percent, incidence increases to between 22 and 53 percent in the military population, she noted, attributing this in part to the severity of injuries sustained in combat (Annegers et al., 1998). Indeed, T.B.I severity is a primary risk factor for P.T.E, Pugh said, with increased risk for individuals who experience penetrating injury, longer periods of loss of consciousness, or longer gaps in memory.

The likelihood of developing P.T.E after a penetrating head injury is approximately 50 percent (Pugh et al., 2021). Other characteristics associated with severe T.B.I, such as prolonged coma, intracranial bleeding, and seizures within a week of injury, are strong predictors of P.T.E. Research suggests that individuals with mild T.B.I are at a slightly higher risk of developing P.T.E than those with no history of T.B.I, she indicated. Pugh explained that while this risk is modest—at about 1.5 percent—it translates to a large number of people at the population level, given the large number of people who experience mild T.B.I. The risk of P.T.E is highest for people who are very young or very old. Although the risk of P.T.E is highest in the first 2 years after injury, it can occur 10 to 20 years or more after T.B.I, Pugh indicated.

Complex Comorbidity in P.T.E

P.T.E is associated with mental health, neurocognitive, and psychosocial issues and with neurological and chronic disease, Pugh described. Treatment resistance to medications and procedures for recurrent seizures is more common among individuals with P.T.E than those with epilepsy alone. Common side effects of antiseizure medications include dizziness, fatigue, and memory problems. Given that people with P.T.E are more likely to take multiple medications to control seizures, she said, an increased medication regimen can magnify these side effects. Pugh underscored the importance of early diagnosis and treatment for P.T.E to mitigate the long-term effects of treatment resistance.

Seizures can involve falls and injuries, creating vulnerability to additional T.B.I's. Moreover, T.B.I comorbidities can become more complex with P.T.E, she noted. For example, people with T.B.I have a higher risk of depression, a risk that is compounded in people with P.T.E. Similarly, anxiety, bipolar disorder, schizophrenia, post-traumatic stress disorder (P.T.S.D), irritability, sleep disorders, suicidal ideation, and suicide attempts and completions are more common in people with P.T.E than in those with T.B.I alone, she reported. Recurrent and difficult-to-control seizures are associated with subsequent neurocognitive conditions such as memory problems, difficulty concentrating, slow processing speed, mild cognitive impairment, and dementia, said Pugh.

Recent studies have found that epilepsy and P.T.E are associated with the emergence of neurological and other chronic diseases, and that prior comorbidities play a role in this association, Pugh indicated. A study found that conditions including stroke, hypertension, cardiovascular disease, and diabetes emerged after epilepsy in a veteran cohort (Pugh et al., 2025). The interaction of T.B.I and epilepsy could create a more significant cluster of comorbidities occurring earlier in people with P.T.E compared to T.B.I alone, epilepsy alone, or controls, Pugh suggested. Moreover, the emergence of chronic disease contributes to the increased risk of mortality seen in people with P.T.E in comparison with T.B.I or epilepsy alone or the absence of either condition, she noted.

Psychosocial Challenges

Pugh emphasized that complex comorbidity and treatment-resistant epilepsy have substantial effects on people with P.T.E and their loved ones and caregivers. For example, fear of seizures can cause effects such as social isolation and reduced physical and emotional quality of life. Noting research gaps regarding psychosocial outcomes of P.T.E, Pugh highlighted a study that found that U.S. military veterans with P.T.E had significantly lower scores for quality of life measures and quality-adjusted life years than those with epilepsy or T.B.I alone. Studies in the civilian sector suggest that people with P.T.E may have more difficulty coping and participating in activities than individuals with T.B.I alone. Evidence indicates that caregivers of relatives with epilepsy experience relationship strain, disruptions in work and daily routine, and mental health conditions such as anxiety, depression, and P.T.S.D, Pugh continued. Emerging data from an ongoing study of the effects of P.T.E found that caregivers of people with P.T.E report higher levels of stress, sleep interference, and poorer health than caregivers of veterans with epilepsy or T.B.I alone. These findings emphasize the need for more comprehensive evaluations of social, emotional, and health outcomes for individuals with P.T.E and their caregivers and family members, she said.

Research Gaps and Next Steps

Addressing P.T.E requires multidisciplinary and person-centered care, Pugh contended, suggesting that clinicians should involve caregivers to the extent approved and requested by the patient to facilitate overall adherence to treatment. These caregivers also need support to maintain their health and well-being, she said. Although research on P.T.E treatments is ongoing, there has so far been little progress in identifying treatments that prevent or address P.T.E specifically, versus epilepsy generally, said Pugh. It is not yet known whether treatment for epilepsy in general will be the most effective treatment option for P.T.E, she added. Few longitudinal studies examine the emergence of and outcomes for P.T.E, and findings from the Transforming Research and Clinical Knowledge in T.B.I (TRACK-T.B.I) study on epilepsy are only beginning to emerge. Pugh emphasized the importance of longitudinal studies to better understand P.T.E comorbidities and psychosocial outcomes in the context of individuals' medical histories. She also emphasized the need to identify treatment strategies for P.T.E to enhance health and well-being for affected people and families.

Pituitary Deficiencies After T.B.I: Long-Term Effects on Health and Recovery

Tamara Wexler, neuroendocrinologist and professor at New York University, discussed T.B.I-related chronic anterior pituitary hormone deficiencies (post-traumatic hypopituitarism, P.T.H.P) and their role in the health of patients after T.B.I. Wexler specified that deficiencies attributed to hypopituitarism may include hypothalamic deficiencies, and that “chronic” in this setting refers to deficiencies beyond at least 3 months. She emphasized that identification and replacement of deficient hormones is important to reverse associated symptoms, which may include cognitive, emotional, and physical effects. Numerous studies have found that P.T.H.P occurs at higher rates after T.B.I in both adults and children, she said (Agha et al., 2005; Bondanelli et al., 2004; Izzo et al., 2016; Kaulfers et al., 2010; Krahulik et al., 2017; Kreber et al., 2016; Niederland et al., 2007; Personnier et al., 2014; Schneider et al., 2006; Silva et al., 2015). After accounting for appropriate evaluations and diagnostic criteria, approximately 25 to 30 percent of adults with persistent T.B.I symptoms have P.T.H.P, Wexler said. In contrast, the prevalence of P.T.H.P in the general population is less than 0.05 percent (Regal et al., 2001).

Pituitary hormone deficiencies can develop after mild or severe T.B.I, said Wexler (Aimaretti et al., 2005; Alavi et al., 2016; Tanriverdi and Kelestimur, 2015; Yang et al., 2016; Yuen et al., 2022). Moreover, P.T.H.P can appear after a delay of months or years following the injury (Aimaretti et al., 2005; Casano-Sancho et al., 2013; Krahulik et al., 2017). Studies of adults and children throughout the first year after injury found that some individuals with normal hormone levels at 3 or 6 months post-T.B.I have a pituitary a deficiency at 12 months postinjury (Aimaretti et al., 2005; Casano-Sancho et al., 2013; Krahulik et al., 2017); recovery was also seen during this time period though was not observed in situations of panhypopituitarism (in which all anterior pituitary hormones are affected). Growth hormone deficiency (G.H.D) is the most frequent pituitary deficiency beyond 1 year post-T.B.I, Wexler noted; within the first year, G.H.D or hypogonadal hypogonadism have been most frequently reported.

Predictive Characteristics and Symptoms

Given the large number of individuals who experience T.B.I, researchers have explored what screening criteria might predict P.T.H.P, said Wexler. Neither the severity nor mechanism of injury appear to be clinically useful markers to predict P.T.H.P; the limited studies of specific settings of injury such as military blast injuries and recurrent sports injuries also report higher levels of injury (Baxter et al., 2013; Ciarlone et al., 2020; Kelly et al., 2014; Lee et al., 2021; Undurti et al., 2018). Imaging should not be used to rule out hormone deficiencies, as individuals with P.T.H.P may have normal imaging results, and clinically useful biomarkers of P.T.H.P are not currently available, she said. Therefore, persistent symptoms after T.B.I or failure to recover as expected should be used as an indication to consider full pituitary evaluation. Sequelae of P.T.H.P include physical, cognitive, and emotional effects, and symptoms may overlap with other post-T.B.I symptoms, she noted.

Sequelae of P.T.H.P may include changes in body composition, skin, and hair; skeletal and cardiovascular changes; executive function decrements; mental fogginess; fatigue and decreased exercise capacity; irregular periods; decreased libido; and mood changes. Moreover, untreated hypopituitarism is associated not only with decreased quality of life but also with increased morbidity and mortality (Wexler, 2023).

The Pituitary and Its Functions

The pituitary manages production of cortisol from the adrenal glands, thyroid hormone from the thyroid gland, estrogen and testosterone from the ovaries and testes, respectively, and growth hormone, Wexler explained. Located at the base of the brain, the pituitary sits in a bony saddle (the sella), and this placement can make it vulnerable to injury and neuroinflammation, she said. Wexler reported that she too often hears from individuals years post-T.B.I who have not been evaluated for P.T.H.P despite continued issues suggestive of hormone deficiencies. This includes issues with executive function, which may be seen in adults with acquired growth deficiency: difficulties with multitasking, organization, focus, cognitive processing speed, and working memory that disrupt employment and home life.

Care providers may fail to conduct G.H.D evaluation in adults who have reached their full height, she noted, despite the multiple functions that growth hormone carries out throughout the body including a role in executive function, cardiovascular risk factors, bone strength, body composition, and energy and exercise capacity. Studies indicate that G.H.D may contribute to quality of life and neurocognitive sequelae after T.B.I and that individuals with T.B.I who have G.H.D fare more poorly than those with sufficient growth hormone levels (Kelly et al., 2014; Kreber et al., 2016). Wexler highlighted that growth hormone replacement in patients with post-T.B.I G.H.D has led to improvements in cognition, body composition, and quality of life (Bhagia et al., 2010; High et al., 2010; Tanriverdi et al., 2010).

Underdiagnosis of Post-T.B.I Pituitary Deficiencies

Despite evidence of the increased risk of pituitary hormone deficiences after T.B.I and the harmful effects of hypopituitarism, P.T.H.P remains underdiagnosed, said Wexler. Factors contributing to this underdiagnosis include lack of awareness among care providers, the overlap of symptoms of P.T.H.P and T.B.I, and incomplete understanding of the diagnosis of pituitary-level hormone deficiencies, she said. For example, screening for thyroid-stimulating hormone (T.S.H) is commonly conducted at annual physicals. Although this test indicates whether the thyroid gland itself is functioning normally, Wexler explained T.S.H alone is insufficient to diagnose hypothyroidism due to a pituitary (or hypothalamic) cause.

A feedback loop occurs in which the pituitary produces T.S.H that stimulates the thyroid gland to make thyroid hormone. In cases in which the thyroid gland is unable to produce sufficient hormone, a functioning pituitary will secrete higher levels of T.S.H. Thus, a high T.S.H reading indicates hypothyroidism. However, if the pituitary or hypothalamus is not functioning properly, it cannot sufficiently increase T.S.H secretion and T.S.H will remain within the normal range.

In this situation, a person with P.T.H.P and hypothyroidism would have a normal T.S.H level and a low level of free T.4 thyroxine hormone. Thus, T.S.H evaluation alone is insufficient in diagnosing central hypothyroidism, Wexler said. Similarly, care providers may inappropriately use insulin-like growth factor 1 I.G.F-1 as the sole test for G.H.D, without recognizing that some individuals with G.H.D have normal I.G.F-1 levels. In women, missed periods may be misattributed to stress or early menopause without testing follicle-stimulating hormone, which would be inappropriately normal in hypogonadism from a pituitary cause.

Wexler emphasized that P.T.H.P is an important sequela of T.B.I that can be diagnosed and treated. All individuals with a history of T.B.I who are experiencing persistent and disruptive signs or symptoms associated with pituitary deficiencies should be considered for full pituitary evaluation, she maintained, and evaluation over time may be warranted. Furthermore, care providers should offer hormone replacement therapy to individuals diagnosed with P.T.H.P via appropriate testing, said Wexler.

Long-Term Risks of Cardiovascular Diseases After T.B.I

Saef Izzy, associate professor at Brigham and Women's Hospital and Harvard Medical School, discussed the increased risk of developing long-term cardiovascular disease in individuals with T.B.I. Cardiovascular issues in T.B.I patients receiving acute care have been reported for more than three decades, Izzy noted. For instance, patients with acute T.B.I have developed cardiac arrythmias, myocardial injuries, and myocardial dysfunction in addition to experiencing adrenergic storms and cytokine releases (Coppalini et al., 2024; Gregory and Smith, 2012; Krishnamoorthy et al., 2017). Research has indicated an association of T.B.I with chronic cardiovascular diseases including hypertension, hyperlipidemia, and some obesity in civilian, military, and professional football populations (Boos et al., 2019; Eric Nyam et al., 2019; Grashow et al., 2023; Harrison et al., 2022; Memmini et al., 2021; Stewart et al., 2022). Some of these studies have limitations including use of patient self-report, small cohorts, or inclusion of patients with preexisting cardiovascular disease, Izzy noted.

A retrospective cohort study using V.A data compared morbidities in 300,000 veterans with a history of T.B.I and 258,000 veterans without T.B.I (Stewart et al., 2022). The study identified a phenotype of composite cardiovascular comorbidity that was present in 28 percent of veterans with penetrating T.B.I. The next highest association with this phenotype was seen in moderate to severe T.B.I, followed by mild T.B.I. Veterans with all forms of T.B.I had higher incidence of cardiovascular comorbidity than veterans without T.B.I.

Izzy and colleagues conducted a 10-year study of T.B.I patients with no preexisting cardiovascular, psychiatric, endocrine, or neurological comorbidities (Izzy et al., 2022). They found that both mild T.B.I and moderate to severe T.B.I were associated with increased cardiovascular risk as defined by coronary artery disease, hyperlipidemia, hypertension, and obesity. Moreover, risk of these comorbidities after T.B.I was increased across age groups, including a significant increase in hypertension risk even in young individuals with mild and moderate to severe T.B.I aged 18 to 40 years, he said. In subsequent research, Izzy and colleagues found that a composite measure of cardiovascular disease aligned with patterns seen in isolated cardiovascular conditions, showing that individuals with mild or moderate to severe T.B.I were more likely to develop the disease compared to the uninjured control group (Izzy et al., 2023). After dipping in middle age, incidence of cardiovascular comorbidities such as hypertension rose in individuals aged 60 years and older, he reported. These findings demonstrate an association between T.B.I and chronic cardiovascular disease, he said.

Numerous factors affect cognitive impairment and cardiovascular dysfunction after T.B.I, Izzy continued, noting that cardiovascular disease may also play a role in chronic neurodegenerative disease, such as dementia (Izzy et al., 2023). Both preinjury factors, such as existing mental health conditions, lifestyle behaviors, and social determinants of health, and injury-specific characteristics such as severity and repetition can significantly influence long-term T.B.I outcomes (see Figure 2 to 3). Izzy highlighted the complex interplay between T.B.I and endocrine, psychiatric, neurological, and/or cardiovascular disorders, emphasizing the need for proactive screening to better define these associations and identify comorbidity-specific risk factors.

Image summary: A conceptual flowchart illustrating how preinjury factors, such as mental health and lifestyle, combine with TBI severity and repetition to drive neurobiological changes and comorbidities. These factors collectively lead to cognitive impairment and cardiovascular dysfunction.

Figure 2 to 3

Potential relationships connecting preinjury factors and brain injury to cognitive and cardiovascular dysfunction, including neurobiological changes, comorbidities, and behavioral or lifestyle factors that may collectively contribute to increased risk. (more...)

Post-T.B.I Dementia

Raquel C. Gardner, associate professor of neurology at Tel Aviv University School of Medicine and Sheba Medical Center, Israel, outlined the increased risk for dementia among individuals with T.B.I, along with modifiable risk factors, associated pathology, and areas for further research. T.B.I is a well-established risk factor for dementia, she said. She highlighted findings from a recent meta-analysis that combined 41 risk estimates from studies involving 7.7 million individuals (Gardner et al., 2023a). The analysis found a 71 percent increased risk for all-cause dementia associated with T.B.I. In certain subpopulations, such as veterans with moderate to severe T.B.I, the increased risk of dementia was as high as 377 percent (Barnes et al., 2018). Gardner noted that differences in dementia risk can stem from the cumulative lifetime exposure to T.B.I, with greater frequency or severity elevating that risk. She noted that that the Lancet Commission on Dementia Prevention, Intervention, and Care formally recognized T.B.I as a modifiable risk factor in 2020, underscoring the strength of the evidence behind this association (Livingston et al., 2020).

Dementia Risk Factors

Research programs on post-T.B.I dementia, including through the Department of War Congressionally Directed Medical Research Program and the Long-Term Impact of Military-Relevant Brain Injury Consortium-Chronic Effects of Neurotrauma Consortium LIMBIC-C.E.N.C, have generated valuable data, Gardner continued. A nationwide cohort study based on data from nearly 300,000 veterans in the Veterans Health Administration system explored whether reducing modifiable dementia risk factors, such as hypertension, diabetes, depression, and P.T.S.D, could help prevent post-T.B.I dementia (Gardner et al., 2023b). The study found that while the risk of dementia associated with these factors was actually lower in veterans with prior T.B.I compared to those without, the prevalence of these conditions was significantly higher among T.B.I-exposed individuals. For instance, hypertension was 1.2 times more common, depression 2.5 times, P.T.S.D 3 times, and epilepsy 7 times more prevalent in veterans with T.B.I compared to veterans without T.B.I. Although modifying these conditions may yield less dementia risk reduction in individuals with T.B.I, Gardner concluded that their high prevalence suggests that addressing them could still have a substantial impact on reducing the overall burden of post-T.B.I dementia.

Pathology of Post-T.B.I Dementia

Researchers have explored whether the pathology of post-T.B.I dementia is the same or different than that of Alzheimer's Disease, said Gardner. A large study of autopsy cohorts and lifetime T.B.I exposure characterized before death found a consistent association of T.B.I with Lewy body pathology, alpha-synuclein (i.e., the pathology of Parkinson's disease and Lewy body dementia), and microvascular ischemia (Crane et al., 2016). Gardner noted that although this 2016 study found no association with amyloid beta—one of the pathognomonic features of Alzheimer's disease—a subsequent cohort study found a higher burden of amyloid beta in individuals with T.B.I (Agrawal et al., 2022). Post-T.B.I dementia may not reflect a single disease pathology, she said, but rather may result from various pathologies that can occur in isolation or in combination in an individual.

Next Steps

The specific pathology of post-T.B.I dementia that develops in an individual will likely depend on the lifetime dose of T.B.I, personal genetics, and other lifetime exposures that increase or reduce risk, Gardner said. Epidemiological studies inform an understanding of the pathophysiology of post-T.B.I dementia, but much remains unknown, she said. With the advent of antiamyloid therapies like lecanemab, Gardner argued for a targeted shift toward screening, diagnosing, and treating post-T.B.I dementia, noting that it remains unclear whether existing Alzheimer's disease research fully applies to post-T.B.I cases and whether emerging blood biomarker tests used to detect brain amyloid in Alzheimer's disease are equally effective for diagnosing post-T.B.I dementia. Addressing these questions is a critical step in scaling up cost-effective screening and treatment, she said.

Discussion

T.B.I and Comorbidity Diagnosis Challenges

During a discussion moderated by Hoffman, Bombardier highlighted that individuals with T.B.I are less likely to be diagnosed and treated for depression postinjury than they were preinjury. He speculated this may stem from clinicians attributing depressive symptoms to T.B.I itself rather than identifying a treatable comorbid condition. This diagnostic overshadowing may lead to undertreatment of mental health issues in T.B.I populations, he said. Pugh emphasized similar diagnostic challenges in post-traumatic epilepsy care, where treatment resistance is significantly higher than in epilepsy alone. She endorsed the need for early T.B.I screening in patients with epilepsy to better anticipate potential resistance and enable proactive education for families.

Overlooked Cognitive and Hormonal Effects

Wexler described how cognitive deficits in T.B.I patients, particularly those with growth hormone deficiency, often go unrecognized because of normative cognitive test results that fail to reflect changes from individual patient baselines. These individuals may struggle with executive tasks, such as time management and self-expression, and are often forced to advocate for their needs despite these impairments, she said. Izzy added that cardiovascular problems in T.B.I patients are often overlooked or attributed solely to brain injury, leading to undertreatment. He advocated for broader screening of cardiovascular comorbidities in T.B.I patients and suggested that precision medicine approaches could help identify those at elevated risk.

Such approaches can improve T.B.I care, Izzy suggested, by identifying subgroups of patients at higher risk for particular symptoms and outcomes based on information on the person and the injury, imaging findings, and other biological and clinical markers. For clinicians and patients, this type of approach could enable more tailored screening and interventions and more proactive management of long-term health effects, he said.

Antiamyloid Therapies and Post-T.B.I Risk

Gardner noted that safety data on administering new antiamyloid drugs like lecanemab to patients with recent T.B.I remain lacking. Many treatment centers exclude these individuals from dementia treatment because of the unknown risks, including amyloid-related imaging abnormalities. She cited recent findings that one in 18 Medicare beneficiaries visited the emergency department for T.B.I over 18 years (Kornblith et al., 2024), underscoring the need for urgent research into the implications of T.B.I on dementia treatment.

Age of Injury and Comorbidity Risk

In response to questions about the influence of age at time of injury on comorbidities, Pugh explained that both P.T.E and epilepsy are more prevalent among the very young and the elderly. Her research on veterans found that individuals reporting moderate or severe T.B.I's at younger ages had increased risk of epilepsy even if their injury was not service related. Wexler added that children, compared to adults, may more frequently recover from injury. Gardner's meta-analysis showed a higher risk of dementia associated with younger age at injury (Gardner et al., 2023a), and a separate California study found that mild T.B.I at age 80 carried similar dementia morbidity as severe T.B.I at age 50 (Gardner et al., 2014).

Izzy again mentioned the increased incidence of cardiovascular comorbidity rates, including hypertension, in individuals aged 18 to 40, regardless of T.B.I severity or previous heart conditions (Izzy et al., 2023). He noted his current research under review shows that some individuals as young as 40 develop dementia post-T.B.I. Bombardier added that while age does not appear to influence depression rates post-T.B.I, there are notable generational and sex-based differences, with higher prevalence among women and younger generations.

Improving Multimorbidity Data Collection and Monitoring

Given the prevalence of multimorbidity and T.B.I, Hoffman asked about approaches to improve data collection and monitoring for these conditions. Wexler emphasized the need for better data collection tools and guidelines for conditions like P.T.H.P, which can be time consuming to diagnose. She highlighted the importance of multidisciplinary care teams and consistent screening for persistent function-limiting symptoms. Pugh noted findings from epilepsy research in post-9/11 veterans, which found that people with preexisting mental health issues often fare worse after a diagnosis of epilepsy. She recommended that ideal epilepsy care teams include mental health providers, neurologists, and primary care clinicians to manage complex comorbidities.

Izzy said that precision medicine approaches that can better track comorbidity trajectories, such as how hypertension may relate to subsequent neuroendocrine or neurological conditions, will aid in monitoring patients and improving long-term outcomes. His team is investigating whether initial brain imaging can be used in identifying the specific location of the brain associated with the cardiovascular issue. For example, he said, researchers have found that the insular cortex, a part of the brain's cerebral cortex that is located beneath a groove called the Sylvian fissure, is linked to the regulation of heart rate and other autonomic body responses, highlighting its role in brain–heart connections.

Biomarkers and T.B.I Diagnosis

Gardner emphasized the usefulness of implementing blood biomarker tests approved by the Food and Drug Administration (e.g., glial fibrillary acidic protein and ubiquitin C-terminal hydrolase) to diagnose mild T.B.I, especially when computed tomography imaging is negative. Many patients discharged from the emergency department without a T.B.I diagnosis experience chronic symptoms that are hard to attribute definitively to T.B.I or psychological trauma, she said. T.B.I and acute psychological stress can also co-occur, such as in military populations that experience blast injuries, and may present similar symptoms years later. These factors complicate the process of diagnosing the cause of subsequent symptoms. Widespread use of biomarker testing soon after injury would improve diagnostic accuracy, she said.

Limitations in Depression Treatment

Bombardier noted that that no biomarkers of depression have yet been identified and current treatments for depression in T.B.I populations—including antidepressants and cognitive behavioral therapy—have shown limited success. He proposed reframing depression as a secondary condition, with treatment strategies tailored to comorbid symptoms like sleep disorders, chronic pain, or P.T.S.D. Incorporating patient-reported outcomes and shared decision making can enhance engagement and effectiveness. This person-centered approach allows clinicians to prioritize interventions based on patient motivation and lifestyle, he said.

Hormonal Deficiencies and Inflammation

Addressing a question about hormone levels and neuroinflammatory signaling, Wexler noted that mouse studies have shown that both growth hormone and testosterone are important for myelin repair. There is a need for further research on the interplay between neuroendocrine pathways and recovery from T.B.I, she said.

Heat Sensitivity and T.B.I

An audience member asked whether a known link exists between T.B.I and fainting in hot weather or crowded environments. Izzy responded that individuals with T.B.I may experience impaired temperature regulation due to hypothalamic damage, making them more vulnerable to heat-related issues like heat exhaustion or heat stroke. He was not aware of specific direct studies on this topic, but a dehydration-induced feeling of lightheadedness (presyncope) is a plausible mechanism, especially in warmer climates. He added that more research is needed to determine whether inflammation or other physiological changes predispose an individual with T.B.I to fainting.

The Broad Effects of T.B.I and the Need for Longer-Term Surveillance

Hoffman reiterated the diagnostic and treatment complexities of T.B.I, noting the challenge posed by overlapping and evolving symptoms. Bombardier expressed concern that conditions such as depression are often misattributed to T.B.I itself, resulting in underdiagnosis and missed opportunities for early intervention in comorbidities like depression and epilepsy. Izzy and Gardner highlighted the need for longer-term research to better capture chronic outcomes such as cardiovascular disease, dementia, and multimorbidity that may emerge 3 to 5 years or more postinjury but are often missed because of short follow-up periods. While the TRACK-T.B.I longitudinal study represents progress, further investment is needed, Gardner said. Izzy concurred, noting that extended study timelines and funding will be essential for improving long-term understanding and care.

Suggestions for Improved Care

With T.B.I affecting millions across the life span, a shift toward precision medicine, extended monitoring, and individualized care is essential to address the broad and complex effect of this condition, the panelists highlighted. Wexler noted that cognitive limitations in T.B.I patients can hinder their ability to self-advocate or even recognize the need for care. Wexler and Pugh called for integrated care models that combine the expertise of neurologists, endocrinologists, physiatrists, primary care providers, and mental health professionals to deliver comprehensive, coordinated treatment.

Gardner and Izzy underscored the value of precision tools such as blood biomarkers and genetic screening to identify individuals with T.B.I at higher risk for poor outcomes. Broader adoption of validated diagnostic tools, akin to those now standard in Alzheimer's care, offers one of the most actionable steps to improving long-term outcomes, Gardner said.