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Military researchers gain new insights into brain injuries

Military personnel sitting at a table collecting data Study team members from Naval Medical Center Camp Lejeune and the Hearing Center of Excellence conduct pre-exposure auditory testing on Marines during an Integrated Training Exercise at Marine Corps Air Ground Combat Center Twentynine Palms, California in January 2020. The CHASMPAS study is working to better understand noise-induced hearing loss by collecting audiometric data before and after noise exposure (Photo by: Quintin Hecht).

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Military researchers have recently found that headache, dizziness and cognitive dysfunction occur far more frequently among military personnel with mild traumatic brain injury than in those without injury. Sleep disorders and emotional issues are also significantly more common in members with this injury.

These findings are from a study supported by the Defense Health Agency’s Hearing Center of Excellence (HCE) that evaluated a battery of neurologic assessment tests to help diagnose mild head injury. The Madigan Army Medical Center at Joint Base Lewis-McChord in Washington, and the Naval Medical Center San Diego in California served as enrollment sites from 2014 through 2017 for the study called, "Assessment of Oculomotor, Vestibular and Reaction Time Response Following a Concussive Event."

The Center for Disease Control and Prevention defines a traumatic brain injury (TBI) as a disruption in the normal function of the brain that can be caused by a bump, blow, or jolt to the head, or penetrating head injury. The severity of a TBI may range from mild, commonly called concussions, to severe. According to the Armed Forces Health Surveillance Branch, mild traumatic brain injury, or mTBI, is the most common traumatic brain injury affecting military personnel, and includes concussion, subconcussion that does not cause symptoms, and exposures to blasts like improvised explosive devices.

"The objective of the research was to collect data to advance our understanding of oculomotor, vestibular and reaction time responses in relation to mTBI," said HCE division chief, Dr. Carlos Esquivel. "Three of the tests yielded an 89% sensitivity and 95% specificity for confirming a current diagnosis of mTBI."

The hearing center is facilitating several other research projects to better understand hearing injury and its connection to traumatic brain injury.

A multi-site field study, called CHASMPAS (Characterization of Acute or Short-term Acquired Military Population Auditory Shifts) has been underway since 2019 to characterize short-term changes in hearing among military personnel exposed to blast. Researchers are using advanced boothless hearing test technology to conduct in-field hearing evaluations immediately before and after a service member's blast exposure, and state-of-art blast measurement technology from the federally funded Massachusetts Institute of Technology - Lincoln Laboratory.

"This comprehensive study approach may identify risk factors, mitigating factors and dose-response relationships, which could result in refinement of acoustic standards, new hearing protection strategies, and direction of future research to explore pharmaceutical intervention for hearing loss," said Dr. Douglas Brungart, chief scientist of the HCE and the National Military Audiology and Speech Center at Walter Reed National Military Medical Center in Bethesda, Maryland.

According to Brungart, so far, roughly 95 service members have taken part in the study with future data collection and analysis planned at Fort Benning, Georgia; Camp Lejeune, North Carolina; and Quantico, Virginia.

Esquivel said the HCE will continue to support the CHASMPAS project and other related ongoing projects, to advance work in this area of study.

According to Esquivel, research efforts to date have shown that people can suffer from a form of hidden injury, signaling the importance of continuing these studies. "When people report having difficulties hearing, we cannot dismiss their complaints when their hearing test results are normal. Research in this area will be critical in understanding these impacts as risk factors, and short-term and long-term auditory effects may be identified from the retrospective and prospective, longitudinal analysis," Esquivel explained.

Additional plans in brain injury research are underway for MAMC and NMCSD to participate in a study called, "Clinical Trial of Etanercept (TNF-a Blocker) for Treatment of Blast-Induced Tinnitus." Led by Wayne State University, the project will test an FDA-approved medication for the treatment of blast-induced tinnitus.

The NMCSD has also started enrolling participants for a study called, "The Use of a Standardized Instrument to Provide Diagnostic and Prognostic Information in Traumatic Brain Injury." This Uniformed Services University of the Health Sciences-funded study is a collaboration with the University of Miami and University of Pittsburgh to evaluate the utility of a multi-modality suite of tests for diagnosing TBI, as well as the ability to provide prognostic information about recovery.

Esquivel explained the symptoms of TBI, such as headaches, hearing loss, and dizziness, generally resolve within six weeks, but for some, these symptoms persist and can worsen over time."For that reason, examining tests to determine the presence of TBI is a pressing need in this field. Equally as important is a test or set of tests that can be prognostic in nature, and predict a person’s return to duty and other activities," said Esquivel.

The center's regional research administrators at MAMC and NMCSD have supported multiple local and multi-site studies sponsored through the Congressionally Directed Medical Research Programs and industry grants. In addition, the HCE research coordination branch supports multi-site hearing injury research in collaboration with WRNMMC to collect data at Marine Corps Base Camp Lejeune, North Carolina; Marine Corps Combat Development Command, Quantico, Virginia; and Ft. Benning, Georgia.

"These research projects are providing invaluable data to address previously identified knowledge gaps in this area, but our work is not done. We must continue to support this area of research as the state of science advances," Esquivel summed up.

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