The report is a product of the VA/HSR Evidence Synthesis Program.

Evidence Brief: Traumatic Brain Injury and Dementia

Traumatic brain injury (TBI) is a common condition among both civilian and military populations. While some TBIs cause acute symptoms that resolve over several weeks or months, evidence accumulated over nearly three decades suggests that TBI may lead to chronic neurodegenerative diseases such as dementia. More public awareness about TBI in active-duty service members as a risk factor for earlier onset of dementia and/or of Chronic Traumatic Encephalopathy (CTE) has increased the urgency to better understand these potential links. In particular, a better understanding of the link between TBI and dementia among Veterans could help VA develop and provide guidance on new screening, diagnosis, and treatment efforts in the future.

The aim of this rapid review was to summarize the best evidence on the comparative prevalence of dementia between Veterans and civilians, and to assess whether certain risk factors (i.e., previous TBIs, era of conflict, and combat exposure) affect the risk and timing of dementia onset among Veterans. Investigators with VA's Evidence Synthesis Coordinating Center in Portland, OR reviewed the literature including: MEDLINE®, Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, PsycINFO, and Google Scholar. Investigators identified 40 studies that were used in this review, which builds on previous evidence synthesis work by focusing on Veteran populations and adding a few key studies including Veterans that were either not yet published or that used a broader range of analytic methods (i.e., hazard ratio, prevalence rates).

Summary of Findings
TBI appears associated with an increased risk of dementia in Veterans. This review found that although few studies have focused on evaluating the association between TBI and dementia in military and Veteran populations, findings of those that did were consistent with those from a 2017 systematic review (Li, et al., 2017) of worldwide general community studies, in suggesting that TBI is associated with increased risk of dementia. In fact, findings from the largest and most recent study in U.S. Veterans showed a dose-response relationship between TBI and dementia diagnosis: Compared to the increased risk of dementia for a mild TBI without loss of consciousness, the association between TBI and dementia grew progressively larger with increasing TBI severity.

Dementia prevalence appears similar in Veteran and non-Veteran populations.
Although no study has directly compared dementia rates in Veterans and non-Veterans in the same sample, estimates from two separate sources suggest that dementia rates appear similar in Veterans (11%) and non-Veterans (range, 9% to 12%) aged 65 years and older. This finding could potentially allay concerns that military service may increase risk of dementia overall.

No studies were found that addressed whether the prevalence of dementia in Veterans varies based on combat deployment history, era of conflict, mode of injury (blast vs non-blast), or number of injuries.

Future Research
Key evidence gaps to consider for future research include direct comparison of dementia rates in Veteran versus non-Veteran populations, the association between TBI and early-onset dementia, and mechanisms of the association between TBI and dementia. As yet, there is no specific guidance on screening, prevention, and rehabilitation of TBI-associated dementia. A critical area of research to support efforts to develop effective treatment and prevention strategies is to better understand the underlying mechanisms of the observed association between TBI and dementia. Although several plausible mechanisms have been proposed, their evidence has been mixed and inconclusive. Additionally, to further understand the comparative prevalence of dementia in Veteran and non-Veteran populations, future studies should ideally directly compare prevalence rates from the same population.

Implications for VHA Practice/Policy
Providers treating individuals with TBI should be aware that while TBI may increase the risk of dementia, not all Veterans experiencing memory and concentration difficulties will develop dementia. Translation of these available and emerging findings of increased risk to clinical practice guidelines to outline refined approaches to clinical examination of early and intermediate TBI evolution also needs to occur going forward, as guided by Patient Care Services and Rehabilitation.

In the interim, clinical recommendations should encourage the incorporation of healthy lifestyle habits (i.e., healthy diet, regular exercise, sleep hygiene, avoidance of alcohol and drugs, etc.) to improve overall health. For detailed guidance on managing all the post-concussion symptoms, providers may access the full Clinical Practice Guidelines package from 2016 (Management of Concussion-mild Traumatic Brain Injury). These guidelines identify the science behind and practical approaches to managing the 20+ symptoms commonly seen following combat (and all) concussions. Additionally, the Chronic Effects of Neurotrauma Consortium (CENC) has established a knowledge translation core to disseminate all CENC findings to the public, service members and Veterans, as well as clinicians and researchers.

Reference
Peterson K, Veazie S, Bourne D, Anderson J. Evidence Brief: Traumatic Brain Injury and Dementia. VA ESP Project #09-199; 2019.

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