Soldiers returning from Iraq and Afghanistan who have suffered severe or moderate traumatic brain injury are at increased risk for certain neurodegenerative symptoms such as Alzheimer-type dementia and parkinsonism, according to an Institute of Medicine report.
The IOM also found limited but suggestive evidence of a link between mild traumatic brain injury (TBI) accompanied by loss of consciousness and Alzheimer-type dementia and parkinsonism.
The findings highlight the potential to underestimate adverse neurologic consequences in returning soldiers, many of whom have been exposed to some type of explosion resulting in traumatic brain injury, said Dr. Samuel J. Potolicchio, professor of neurology at George Washington University in Washington, and a member of the IOM Committee on Gulf War and Health.
“We really have absolutely no idea about how much of a blast injury you need in order to have a neurological health outcome,” Dr. Potolicchio said.
Physicians need to take a careful history of all returning service members to determine their exposure to explosions and other hazards in a war zone, he said.
The increasing power of explosive devices as well as other weapons accounts for rates of nonpenetrating TBI and blast-related injury in the current Iraq and Afghanistan wars that are much higher than in previous conflicts. During the Vietnam War, for example, TBI accounted for about 12%–14% of combat casualties, compared with about 22% in Iraq and Afghanistan, according to the IOM report.
The Department of Defense estimates that more than 5,500 military personnel have suffered TBI in Iraq and Afghanistan as of January 2008.
Most of these veterans will seek medical treatment in a Department of Veterans Affairs clinic, but VA providers may be unable to keep up with the demand in certain areas, or the VA clinic may be too far away from the patient's home and civilian neurologists might see some of these patients, Dr. Potolicchio noted.
The IOM committee reviewed about 1,900 peer-reviewed studies to determine the long-term consequences of exposure to both penetrating and closed TBI, including blast injuries. The committee focused on clinical and epidemiologic studies of adults who suffered long-term health effects due to occupational injury, motor vehicle accident, sports injury, gunshot wound, and military combat. The review was requested by officials at the VA.
In addition to the evidence of neurodegenerative effects, the IOM committee found a positive association between moderate or severe TBI and hypopituitarism and growth hormone insufficiency. There also was a positive link to long-term adverse social functioning, such as unemployment and diminished social relationships. Moreover, mild to severe TBI was associated with depression, aggressive behaviors, and postconcussion symptoms, including memory problems, dizziness, and irritability.
The committee also identified sufficient evidence of a causal relationship between penetrating TBI and unprovoked seizures, and severe or moderate TBI and unprovoked seizures.
Despite the existing evidence, the committee noted a need for continued research, with a special emphasis on blast-induced neurotrauma. The Department of Defense and the VA should support prospective, longitudinal studies that could confirm reports of long-term or latent effects of blast exposure, and answer questions about recovery times and other factors that could improve or worsen outcomes.
To gain more data on the effects of TBI, the IOM committee also called on the VA to include a comparison group of veterans as part of its Traumatic Brain Injury Veterans Health Registry. One of the flaws in the available evidence is the lack of adequate control groups, the committee wrote.
The committee called for the Defense Department to conduct predeployment neurocognitive testing of all deployed military personnel and postdeployment testing of a representative sample of military personnel, including those with TBI, those with non-TBI injuries, and uninjured service members who did not have blast exposure. This type of information would help researchers address questions that cannot be answered with the currently available research—such as the predeployment cognitive ability of an individual and the extent to which TBI affects baseline functioning.