Summary: Military and law enforcement personnel who are routinely exposed to low levels of blasts, such as from high-caliber firearms while training, have higher levels of biomarkers associated with TBI.
Source: Walter Reed Army Institute of Research
Scientists at the Walter Reed Army Institute for Research demonstrated that biomarkers associated with traumatic brain injury were elevated among law enforcement and military personnel, particularly in active duty participants with longer duration of service. Most notably, these elevated biomarker levels were observed in individuals without a diagnosed brain injury or concussion.
Some law enforcement and military personnel are regularly exposed to low levels of blast, particularly during training, due to the use of explosive charges and high caliber weapons. Understanding effects from these occupational exposures is a military health care priority to improve diagnosis and mitigation of ill effects.
While repeated exposure to low level blast is not known to result in clinically diagnosed traumatic brain injury, exposures have been linked to a series of reported symptoms such as headaches, fatigue, dizziness, memory difficulties, and tinnitus (ringing in the ears) — collectively referred to as “breacher’s brain” among members of affected communities.
This study, published in the Journal of the American Medical Association, measured neurotrauma biomarker concentrations in blood samples from 106 military and law enforcement personnel who were not actively engaged in training or physical activity at the time of blood collection and compared those concentrations with commercially available samples from individuals who were similar in sex and age but unlikely to have been exposed to blast.
“We found that five biomarkers previously associated with TBI and brain diseases were elevated among personnel when compared to controls,” said Dr. Angela Boutte, lead author on the paper and a researcher at the WRAIR Brain Trauma Neuroprotection branch.
“Given the difficulty of identifying and evaluating injury associated with repeated low level blast exposure, we hope these data are the first step in our collective goal to identify objective biomarkers as clinically relevant diagnostic tools.”
Dr. Bharani Thangavelu and Dr. Walter Carr, WRAIR brain health researchers and co-authors, emphasized the potential impact of blast exposure experienced by military personnel stating, “Low level blast exposure in routine military training should not be expected to result in acute, gross behavioral deficits for the majority of personnel. However, repeated exposure across years does correlate with symptomology, especially when a history of chronic exposure is exacerbated by new, large magnitude exposures.”
Efforts to identify and quantify the impact of blast and traumatic brain injury on Service Members have increased dramatically in recent years, including initiatives in response to Congressional mandates. Biomarkers of blast effects on brain health will be a useful tool in this effort, especially as tools that augment decision-making based on symptoms reported by personnel.
Importance There is a scientific and operational need to define objective measures of exposure to low-level overpressure (LLOP) and concussion-like symptoms among persons with specialized occupations.
Objective To evaluate serum levels of neurotrauma biomarkers and their association with concussion-like symptoms reported by LLOP-exposed military and law enforcement personnel who are outwardly healthy and cleared to perform duties.
Design, Setting, and Participants This retrospective cohort study, conducted from January 23, 2017, to October 21, 2019, used serum samples and survey data collected from healthy, male, active-duty military and law enforcement personnel assigned to operational training at 4 US Department of Defense and civilian law enforcement training sites. Personnel aged 18 years or older with prior LLOP exposure but no diagnosed traumatic brain injury or with acute blast exposure during sampling participated in the study. Serum samples from 30 control individuals were obtained from a commercial vendor.
Main Outcomes and Measures Serum levels of glial fibrillary acidic protein, ubiquitin carboxyl hydrolase (UCH)-L1, neurofilament light chain, tau, amyloid β (Aβ)-40, and Aβ-42 from a random sample (30 participants) of the LLOP-exposed cohort were compared with those of 30 age-matched controls. Associations between biomarker levels and self-reported symptoms or operational demographics in the remainder of the study cohort (76 participants) were assessed using generalized linear modeling or Spearman correlations with age as a covariate.
Results Among the 30 randomly sampled participants (mean [SD] age, 32 [7.75] years), serum levels of UCH-L1 (mean difference, 4.92; 95% CI, 0.71-9.14), tau (mean difference, 0.16; 95% CI, −0.06 to 0.39), Aβ-40 (mean difference, 138.44; 95% CI, 116.32-160.56), and Aβ-42 (mean difference, 4.97; 95% CI, 4.10-5.83) were elevated compared with those in controls. Among the remaining cohort of 76 participants (mean [SD] age, 34 [7.43] years), ear ringing was reported by 44 (58%) and memory or sleep problems were reported by 24 (32%) and 20 (26%), respectively. A total of 26 participants (34%) reported prior concussion. Amyloid β-42 levels were associated with ear ringing (F1,72 = 7.40; P = .008) and memory problems (F1,72 = 9.20; P = .003).
Conclusions and Relevance The findings suggest that long-term LLOP exposure acquired during occupational training may be associated with serum levels of neurotrauma biomarkers. Assessment of biomarkers and concussion-like symptoms among personnel considered healthy at the time of sampling may be useful for military occupational medicine risk management.