According to researchers at Duke Medicine and the U.S. Department of Veterans Affairs, veterans who have exposed to blasts and do not report signs of traumatic brain injury (TBI) may still have damage to the brain's white matter similar to veterans with TBI.
The findings, published in the Journal of Head Trauma Rehabilitation, suggest that a lack of apparent TBI symptoms following an explosion may not precisely portray the degree of brain injury.
Veterans of recent military conflicts in Iraq and Afghanistan often have a history of exposure to explosive forces from bombs, grenades, and other devices, although relatively little is known about whether this injures the brain. However, evidence is piling up, especially among professional athletes, that subconcussive events have an effect on the brain.
"Similar to sports injuries, people near an explosion assume that if they don’t have clear symptoms, losing consciousness, blurred vision, headaches, they haven’t had injury to the brain. Our findings are important because they’re showing that even if you don’t have symptoms, there may still be damage,” said senior author and associate professor of psychiatry and behavioral sciences at Duke University School of Medicine and a psychiatrist at the Durham Veterans Affairs Medical Center, Rajendra A. Morey, M.D.
Researchers in the Mid-Atlantic Mental Illness Research, Education and Clinical Center at the W.G. (Bill) Hefner Veterans Affairs Medical Center in Salisbury, N.C., examined 45 U.S. veterans who volunteered to participate in the study.
The veterans, who served since September 2001, were separated into three groups: veterans with a history of blast exposure with symptoms of TBI; veterans with a history of blast exposure without symptoms of TBI; and veterans without blast exposure. The study primarily focused on veterans with primary blast exposure, or blast exposure without external injuries, and did not include those with brain injury from direct hits to the head.
In order to measure injury to the brain, the researchers used a type of MRI called Diffusion Tensor Imaging (DTI). DTI can spot injury to the brain’s white matter by measuring the flow of fluid in the brain. In healthy white matter, fluid moves in a directional pattern, implying that the white matter fibers are undamaged. Injured fibers allow the fluid to diffuse.
White matter is the connective wiring that joins different regions of the brain. Since most cognitive processes involve several parts of the brain operating together, injury to white matter can significantly harm the brain’s communication network and may result in cognitive ailments.
Both cohorts of veterans who were near an explosion, regardless of whether they had TBI symptoms, demonstrated a tremendous amount of injury as opposed to the veterans not exposed to an explosion. The injury was not restricted to one area of the brain, and each individual had a different pattern of injury.
Using neuropsychological testing to evaluate cognitive performance, the researchers found a link between the amount of white matter injury and changes in reaction time and the ability to switch between mental tasks. However, brain injury was not asscociated to performance on other cognitive tests, including decision-making and organization.
“We expected the group that reported few symptoms at the time of primary blast exposure to be similar to the group without exposure. It was a surprise to find relatively similar DTI changes in both groups exposed to primary blast. We are not sure whether this indicates differences among individuals in symptoms-reporting or subconcussive effects of primary blast. It is clear there is more we need to know about the functional consequences of blast exposures,” said research health scientist at the W.G. (Bill) Hefner Veterans Affairs Medical Center and the study’s lead author, Katherine H. Taber, Ph.D.
Given the study’s findings, the researchers noted clinicians treating veterans should take into account a person’s exposure to explosive forces, even among those who did not initially show symptoms of TBI. In the future, they may use brain imaging to support clinical tests.
“Imaging could potentially augment the existing approaches that clinicians use to evaluate brain injury by looking below the surface for TBI pathology,” Morey said.
The researchers said that the results are at this time preliminary, and should be duplicated in a much larger study.