By Brenda L. Mooney
SALISBURY, NC – Veterans exposed to explosions during deployment but not reporting common symptoms of traumatic brain injury (TBI) could have similar damage to the brain’s white matter, according to a new study.
In a small study published recently in the Journal of Head Trauma Rehabilitation
, researchers at the VA and Duke University School of Medicine point out that the full extent of brain injury from explosions cannot be determined by symptoms alone.1
The study is the latest to suggest that subconcussive events have an effect on the brain, which is especially significant because so many veterans of recent military conflicts in Iraq and Afghanistan have had exposure to explosive forces from bombs, grenades and other devices.
According to past research, as many as 20% of the 2.3 million troops deployed to Iraq and Afghanistan since 2001 could have suffered a TBI as a result of exposure to improvised explosive devices (IEDs) and other incendiary weapons.
Rajendra A. Morey, MD
“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, MD, associate professor of psychiatry and behavioral sciences at Duke University School of Medicine and a psychiatrist at the Durham, NC, VAMC. “Our findings are important because they’re showing that, even if you don’t have symptoms, there may still be damage.”
The findings are based on 45 volunteer veterans who served in the military after September 2001 and who had primary blast exposure without external injuries from direct hits to the head. Researchers from the W.G. (Bill) Hefner VAMC in Salisbury, NC, divided the veterans into three groups: those with a history of blast exposure with symptoms of TBI; those with a history of blast exposure without symptoms of TBI; and those without blast exposure.
To measure injury, the researchers used Diffusion Tensor Imaging (DTI), which measures the flow of fluid in the brain. Injured fibers allow the fluid to diffuse while, in healthy white matter, fluid moves in a directional manner, suggesting that the white matter fibers are intact.
The researchers found that the veterans in both groups near an explosion showed significant injuries, even if they had no TBI symptoms, compared to those without blast exposure. The injuries were not in one area of the brain; in fact, each veteran had a different pattern of injury.
With neuropsychological testing to assess cognitive performance, the researchers found a relationship between the amount of white matter injury and changes in reaction time and the ability to switch between mental tasks. Brain injury was not linked to performance on other cognitive tests, however, 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,” said lead author Katherine H. Taber, PhD. “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.”
Clinicians treating veterans should take into account exposure to explosive forces, even when no TBI symptoms were present, according to the authors, who suggest that brain imaging could be used in the future to enhance diagnosis and treatment.
“Imaging could potentially augment the existing approaches that clinicians use to evaluate brain injury by looking below the surface for TBI pathology,” Morey said.
“These results suggest that lack of clear TBI symptoms following primary blast exposure may not accurately reflect the extent of brain injury,” the authors conclude. “If confirmed, our findings would argue for supplementing the established approach of making diagnoses based purely on clinical history and observable acute symptoms with novel neuroimaging-based diagnostic criteria that ‘look below the surface’ for pathology.”
The researchers called for a larger study to replicate their results.
This study was supported by a grant from the DoD’s Joint Improvised Explosive Device Defeat Organization and the VHA’s Rehabilitation Research and Development group.
Taber KH, Hurley RA, Haswell CC, Rowland JA, Hurt SD, Lamar CD, Morey RA. White Matter Compromise in Veterans Exposed to Primary Blast Forces. J Head Trauma Rehabil
. 2014 Mar 4. [Epub ahead of print] PubMed PMID: 24590156.
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