By Judy George, Deputy Managing Editor, MedPage Today
June 18, 2026
The traditional clinical understanding of traumatic brain injury (TBI) has long been framed as a singular event—a discrete moment of trauma leading to long-term neurologic sequelae. However, a significant new retrospective study published in the journal Neurology challenges this unidirectional narrative. The research, which analyzed data from thousands of U.S. military veterans, suggests a "bidirectional" relationship between TBI and several major neurological disorders.
The findings indicate that not only does TBI serve as a precursor to conditions like dementia and epilepsy, but these pre-existing neurological conditions may themselves be significant risk factors for sustaining a TBI in the first place. This circular link suggests that clinicians must fundamentally shift their approach to geriatric care, moving from reactive treatment to proactive, preventative screening.
The Core Findings: A Two-Way Street
Led by Carrie Peltz, PhD, of the San Francisco Veterans Affairs Health Care System, the research team conducted an extensive review of veterans aged 55 and older. The study highlights that the relationship between TBI and neurodegeneration is more complex than previously assumed.
When looking at the data, the researchers found that older adults who had sustained a TBI were significantly more likely than their counterparts without TBI to have received a prior diagnosis of:
- Epilepsy: 4.4 times more likely
- Stroke: 3.2 times more likely
- Dementia: 3.1 times more likely
- Parkinson’s disease: 3.0 times more likely
Conversely, when the researchers analyzed the risk of developing these conditions after a TBI, the numbers remained striking. In the year following a TBI, veterans faced a 2.29-fold increase in the risk of epilepsy, an 1.83-fold increase in stroke, and a 1.24-fold increase in dementia. Parkinson’s disease remained a notable exception, with rates appearing similar before and after the injury, suggesting a stronger correlation in the "pre-injury" direction for this specific condition.
Chronology of the Investigation
The investigation spanned a comprehensive 22-year period, utilizing records from Veterans Health Affairs facilities between October 1999 and September 2021. To ensure the robustness of the data, the researchers employed a rigorous matching protocol.
The final cohort consisted of 13,801 veterans who had experienced an "acute TBI"—defined as a diagnosis documented on the same day as an emergency department visit accompanied by a diagnostic CT or MRI scan within 24 hours. These individuals were matched against a control group of 41,403 veterans without TBI, accounting for critical demographic variables including age, sex, race, ethnicity, and the date of the medical encounter.
The researchers analyzed ICD (International Classification of Diseases) codes to track the incidence of these four neurological conditions. For the TBI cohort, the window of analysis was one year before and one year after the brain injury. For the non-TBI group, a two-year period was observed to maintain statistical parity. By excluding individuals who had these conditions prior to the one-year study window, the team could isolate "incident" cases, ensuring that the findings reflected new diagnoses rather than pre-existing chronic issues.
Supporting Data and Demographics
The study population provided a clear window into the veteran experience, though it highlighted a specific demographic profile common in VA healthcare systems. The study group was predominantly male (96.5%) with an average age of 77.8 years. The racial and ethnic breakdown was 81% white, 12.8% Black, 3.5% Hispanic, and 1% Asian.
While previous research has established that TBI can double the risk of dementia or increase the likelihood of epilepsy and stroke, this study is among the first to quantify the "reverse" causality. By identifying that neurological decline often precedes the physical trauma of a brain injury, the study helps explain why older adults are particularly vulnerable to falls—the most common mechanism for TBI in the elderly.
The data suggests that the cognitive and motor impairments caused by conditions like Parkinson’s or early-stage dementia create a feedback loop: a patient with undiagnosed neurological impairment suffers a fall, sustains a TBI, and that TBI subsequently accelerates the progression of the underlying condition.
Official Perspective and Clinical Implications
Dr. Peltz and her colleagues believe these findings are a call to action for the medical community. "Our findings raise the possibility that dementia, stroke, epilepsy, and Parkinson’s disease are themselves risk factors for TBI in older people," Peltz stated.
The mechanism, she explains, is largely functional. Neurological disorders often degrade motor control, balance, gait, and spatial awareness—all of which are essential to navigating the environment safely. When these functions are compromised, the likelihood of a fall increases exponentially.
Recommendations for Practice
In light of these findings, the research team is advocating for a shift in clinical policy:
- Mandatory Fall-Risk Screening: Every older patient diagnosed with a neurological disorder should be automatically screened for fall risk.
- Rapid Referral: Patients identified as high-risk should be immediately referred to physical therapy (PT) or occupational therapy (OT).
- Home Environment Audits: Healthcare providers should educate families on removing household tripping hazards and installing supportive equipment like grab bars.
- Medication Reconciliation: Periodic review of prescriptions is necessary, as many medications used to treat neurodegenerative symptoms can inadvertently increase the risk of dizziness or falls.
Limitations and Future Directions
Despite the significance of the study, the authors were transparent about its limitations. The primary constraint was the reliance on medical records for the follow-up period. Because the study required records for one year post-TBI, it excluded veterans with severe brain injuries who passed away within that first year.
Furthermore, the study likely undercounted mild TBI cases, as many older adults may suffer minor head impacts that do not necessitate an emergency department visit or imaging. Because the study was confined to the veteran population, the researchers noted that the findings might not be directly generalizable to the broader civilian population, although the biological mechanisms are likely universal.
"Future studies with richer phenotyping, prospective ascertainment, and longer follow-up will be informative," the researchers concluded in their report. They emphasized that using diagnostic codes alone, while efficient for large-scale retrospective studies, may miss early-stage or sub-clinical disease progression, necessitating more granular, longitudinal data collection in future iterations of this work.
Conclusion: A Paradigm Shift in Geriatric Neurology
The study by Peltz et al. serves as a sobering reminder that the aging brain is a complex, fragile ecosystem. By identifying the bidirectional nature of TBI and neurological disease, the research provides a vital roadmap for preventative medicine.
For veterans and the elderly at large, the takeaway is clear: the prevention of brain injury is not merely about avoiding trauma; it is about managing the neurological health of the patient to prevent the accidents that lead to trauma. As the population continues to age, integrating fall prevention into the standard care of patients with dementia, stroke, and Parkinson’s may prove to be one of the most effective strategies for preserving both the physical and cognitive health of our older citizens.
