Veterans who have been exposed to nearby explosions, but who lack clear symptoms of traumatic brain injury (TBI) may still have damage to the brain’s white matter similar to veterans with TBI, according to new research at Duke Medicine and the U.S. Department of Veterans Affairs.
White matter is the connective tissue that links different areas of the brain. Because most mental processes involve various parts of the brain working together, injury to white matter can weaken the brain’s communication network and may result in cognitive problems.
Veterans who were posted in Iraq and Afghanistan were often exposed to explosive forces from bombs, grenades and other devices. Although the full consequences of being near a blast are still unknown, new evidence is building — particularly 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,” said senior author Rajendra A. Morey, M.D., associate professor of psychiatry and behavioral sciences at Duke University School of Medicine and a psychiatrist at the Durham Veterans Affairs Medical Center.
“Our findings are important because they’re showing that even if you don’t have symptoms, there may still be damage.”
For the study, researchers evaluated 45 U.S. veterans from 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 research 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.
To measure the extent of injury on the brain, researchers used diffusion tensor imaging (DTI), which can detect injury to the brain’s white matter by measuring the brain’s flow of fluid. In healthy white matter, fluid moves in a directional manner, while injured fibers cause the fluid to disperse.
The findings reveal that veterans who were in close proximity to an explosion, regardless of whether they had TBI symptoms, showed a significant amount of injury compared to the veterans not exposed to a blast. The injury was not isolated to one area of the brain, and each individual had a different pattern of injury.
Researchers also found a link between the amount of white matter injury to changes in reaction time and the ability to switch between mental tasks. However, no link was found between brain injury and decision-making and organizational skills.
“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,” said Katherine H. Taber, Ph.D., a research health scientist at the W.G. (Bill) Hefner Veterans Affairs Medical Center and the study’s lead author.
“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.”
Researchers suggest that doctors take into consideration a person’s exposure to explosive forces, even those who did not initially show symptoms of TBI. In the future, brain imaging may be used 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 study is published in the Journal of Head Trauma Rehabilitation.
Source: Duke University