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Author: Daniel P. Perl
Traumatic brain injury (TBI) represents a major public health issue in the United States: it is estimated that 5.3 million Americans have long-term disabilities related to a TBI (Thurman et al. 1999), equivalent to the number of patients with Alzheimer’s disease (Alzheimer’s Association 2015).
According to the Centers for Disease Control and Prevention, each year patients suffering a TBI cause at least 2.2 million visits to an emergency room in the United States (Faul et al. 2010). The more severe forms of TBI lead to 280,000 hospitalizations and are responsible for 52,000 deaths annually. In fact, TBI is the leading cause of death of individuals between the ages of 1 and 44 years. The annual number of deaths associated with TBI exceeds those associated with more widely acknowledged health problems, such as breast cancer (40,000 deaths/year) and influenza (50,000 deaths/year) (Faul et al. 2010).
Among the more common events leading to TBI are falls, motor vehicle accidents, assaults, and participation in contact sports. But a significant number of US citizens who suffer from the long-term effects of a TBI are current or retired servicemembers, especially those who served in Iraq and Afghanistan. Yet it is not known whether or how their symptoms differ from those of nonbattlefield TBI.
Given the sizable number of those affected, it is unclear why TBI remains underrecognized as a major public health problem by the lay public and those who establish policies for research funding.
Defining TBI and Concussion
Most TBIs—civilian and military—are classified as mild, commonly referred to as concussion. Concussion is generally defined as a transient loss of neurologic function following a blow to the head. This alteration of neurologic function may be a loss of consciousness (being “knocked out”), and many people mistakenly assume that loss of consciousness is required for a diagnosis of concussion. But symptoms may include an episode of temporary disorientation or a brief loss of memory of events without any loss of consciousness.
Concussion represents a clinical phenomenon and is not necessarily associated with any specific morphologic alterations in brain tissue integrity. Indeed, by definition, cases of concussion may not show any morphologic abnormalities on routine brain imaging by either computed tomography (CT) scanning or magnetic resonance imaging (MRI) studies.
More serious forms of TBI are characterized by the presence of a variety of abnormalities in and around the brain, including focal damage to brain tissue and the accumulation of blood in the brain itself or adjacent to it.
TBI in Military Servicemembers
Mild TBIs are common occurrences among people who serve in the military, and most are identical in nature to those seen in civilians. In fact, approximately 50 percent of new enrollees in the military indicate that they have already had at least one TBI.
On the battlefield, however, most brain injuries that military servicemembers experience are of a very different nature and represent some unique challenges.
During the past 14 years of US engagement in the wars in Iraq and Afghanistan the enemy has made use of a particularly potent weapon, the improvised explosive device (IED). IEDs are constructed using high explosive charges and metallic fragments (e.g., ball bearings) placed in a container that is hidden from sight, typically buried under a roadway. The device is detonated remotely when the target is in the vicinity (figure 1).
IEDs can have devastating effects on vehicles and personnel. They produce a rapidly expanding high-pressure blast wave that may be powerful enough to throw a vehicle roughly the size and weight of a city garbage truck more than 30 feet into the air.
In previous wars, when servicemembers lacked modern protection, exposure to an IED would have been fatal. Improvements in the design of body armor and modern helmets have saved the lives of countless servicemembers involved in combat. Those in the vicinity of an IED explosion commonly survive and appear to be relatively unharmed. However, initial data indicate that 84 percent of all IED-related concussions occur within 10 meters of the blast, and 93 percent within 30 meters (IOM 2014).
Symptoms and Diagnosis
A significant percentage of servicemembers who have been in close proximity to detonated high explosives such as IEDs subsequently develop persistent neurologic and behavioral symptoms. These may include headaches, sleep disorders, memory problems, difficulty concentrating, depression, anxiety, and a tendency toward suicide. Most of these symptoms are referred to under the term postconcussive syndrome (PCS), but there is a significant overlap between this relatively nonspecific entity and the closely related mental health problem referred to as posttraumatic stress disorder (PTSD). Sorting out the differences between these two conditions, PCS and PTSD, has been a significant challenge for clinical evaluators of both active duty servicemembers and veterans.
Animal experiments have shown that the blast wave produced by a high explosive can pass through the skull as a pressure pulse and exert a force on brain tissues, but the specific effects on human brain tissue remain unclear (Rosenfeld et al. 2013). The study of such effects is complicated by the fact that there are very few real-life examples of pure blast injury. Almost invariably, with blast exposure come additional injuries (e.g., from flying fragments of shrapnel and other debris) as well as impact trauma (e.g., from the individual’s body being propelled at high speed into a solid object from the blast wind that accompanies the explosion). Better understanding of the variety of effects requires examination of many brain specimens from individuals who have suffered blast explosive TBI, with both short-term and prolonged survival after the event.
Adding to the difficulty of diagnosis and treatment, many servicemembers have suffered multiple episodes of blast-related TBI during their repeated deployments to Iraq and Afghanistan. These servicemembers may be at risk for chronic traumatic encephalopathy (CTE), a progressive neurodegenerative disorder that has been seen almost exclusively among athletes who engage in contact sports (e.g., boxing, football, and hockey) and are exposed to repeated impact TBIs (as discussed in other papers from this symposium). CTE is defined by the presence of focal accumulations of the tau protein in the brain in a unique and characteristic distribution pattern, primarily within neurons, astrocytes, and neuronal processes. But only a small number of cases of CTE in servicemembers exposed to IEDs during deployment have been reported in the medical literature (Goldstein et al. 2012; McKee and Robinson 2014; Omalu et al. 2011).
Further complicating the picture is the fact that some servicemembers shown to have CTE at autopsy had participated in contact sports or experienced other types of TBI-inducing incidents such as falls or motor vehicle accidents. Therefore, whether repeated blast TBI alone leads to CTE remains unclear, and how frequent this consequence might be among military personnel is also unknown. The answers to such questions can help determine appropriate diagnosis and treatment for active servicemembers and veterans.
Although high explosives were introduced into warfare in World War I, there has been very little study over the past 100 years of the pathology of blast TBI in the human brain and it is still not known whether military TBI is different from civilian TBI.
Exposure to a blast wave related to an IED or similar explosive would appear to cause a unique form of traumatic injury, especially when such exposures are multiple. But the data needed to make such a determination are scarce. Clearly, there will be some overlap between what is seen in TBI among civilians and the TBI experienced by military personnel. Much more study is needed to sort out the differences between the two.
At the Uniformed Services University of the Health Sciences (USUHS), the congressionally mandated Center for Neuroscience and Regenerative Medicine (CNRM) has established a repository of brain tissue donated for use in research. This unique facility collects specimens from either active duty or former servicemembers, both with and without a history of TBI in their military careers. The tissue specimens are made available to researchers for the study of TBI, especially as it is encountered among military personnel.
It is through the study of donated brain specimens that many important questions can be answered. For more information on the CNRM-USUHS Brain Tissue Repository or to arrange for brain donation, please visit our website (www.researchbraininjury.org) or call 855-366-8824.
Alzheimer’s Association. 2015. 2015 Alzheimer’s Disease Facts and Figures. Chicago. Available at www.alz.org/facts/overview.asp.
Faul M, Xu L, Wald MM, Coronado VG. 2010. Traumatic Brain Injury in the United States: Emergency Department Visits, Hospitalizations, and Deaths 2002–2006. Atlanta: Centers for Disease Control and Prevention, National Center for Injury Prevention and Control.
Goldstein LE, Fisher AM, Tagge CA, Zhang XL, Velisek L, Sullivan JA, Upreti C, Kracht JM, Ericsson M, Wojnarowicz MW, and 25 others. 2012. Chronic traumatic encephalopathy in blast-exposed military veterans and a blast neurotrauma mouse model. Science Translational Medicine 4:134ra60.
IOM [Institute of Medicine]. 2014. Gulf War and Health, vol 9: Long-Term Effects of Blast Exposures. Washington: National Academies Press.
McKee AC, Robinson ME. 2014. Military-related traumatic brain injury and neurodegeneration. Alzheimer’s & Dementia 10:S242–S253.
Omalu B, Hammers JL, Bailes J, Hamilton RL, Kamboh MI, Webster G, Fitzsimmons RP. 2011. Chronic traumatic encephalopathy in an Iraqi war veteran with posttraumatic stress disorder who committed suicide. Neurosurgery Focus 31(5):E3.
Rosenfeld JV, McFarlane AC, Bragge P, Armonda RA, Grimes JB, Ling GS. 2013. Blast-related traumatic brain injury. Lancet Neurology 12(9):882–893.
Thurman D, Alverson C, Dunn K, Guerrero J, Sniezek J. 1999. Traumatic brain injury in the United States: A public health perspective. Journal of Head Trauma Rehabilitation 14(6):602–615.
The opinions expressed herein are those of the author and are not necessarily representative of those of the Uniformed Services University of the Health Sciences (USUHS), the Department of Defense (DOD), or the United States Army, Navy, or Air Force.