Clues to Blast-Related Brain Injury

The blasts caused by improvised explosive devices in Iraq and Afghanistan appear to inflict a fundamentally different type of brain damage than do more traditional sources of concussions, such as blunt trauma. The findings point toward new approaches to diagnosing and monitoring these injuries, which have been a huge concern to the military in recent years. The research also begins to resolve a controversy in brain-injury research–whether soldiers who are near an explosion but don’t get hit in the head can still suffer a unique type of brain damage.

Regular concussions are typically caused by direct impact to the head, such as in a fall, or acceleration injuries, as in car accidents. In contrast, blast-induced brain injuries can include both of these factors as well as one that is unique to explosions–a rapid pressure wave that may wreak its own havoc on the brain. As a growing number of troops return from Iraq and Afghanistan with signs of brain injury–post-deployment surveys suggest that 10 to 20 percent of all deployed troops have experienced concussions–the military has been under increasing pressure to understand how this pressure wave affects the brain, as well as how best to diagnose and treat the resulting injuries.

Typically, damage from concussions does not show up on traditional medical imaging tests, such as CT scans or MRIs. But scientists have recently begun using a variation of MRI known as diffusion tensor imaging (DTI) to detect damage to the brain’s white matter–the neural wiring that connects cells–after mild traumatic brain injury.

In the new study, David Moore, a neurologist and deputy director for research at the Defense and Veterans Brain Injury CenterinWashington, D.C., and colleagues used DTI to assess troops who had been diagnosed with mild traumatic brain injury following a blast, a direct impact, or an acceleration-induced injury several months prior, as well as healthy people who had never suffered a concussion. They found that those with blast-linked trauma had a more diffuse pattern of damage to the white matter, described as a “pepper-spray pattern,” than those whose concussions were caused by direct impact or acceleration. The research was presented at the World Congress for Brain Mapping and Image Guided Therapy conference in Boston last month.

Moore’s team also found signs of inflammation in those people’s brains several months after they experienced the blast, when most symptoms of concussion have typically faded away. “We see evidence of prolonged subacute to chronic inflammatory effects [in these patients],” says Moore. “It indicates something unique about the blast itself.”

The findings build on a growing number of clues illuminating blast-related brain injury. By studying Marines being trained to set controlled explosions, as well as pigs exposed to explosions, Geoffrey Ling, a neurologist and scientist at the Defense Advanced Research Projects Agency, and colleagues found signs of brain inflammation in the blood, even when no other signs of injury were present.

“We are starting to understand the mechanisms of the blast, and that’s leading us to ask different questions,” says Michael Jaffee, national director of the Defense and Veterans Brain Injury Center. For example, scientists now want to better clarify the role of inflammation in this type of injury. DTI might also prove useful for diagnosing blast-related concussions and assessing recovery, he says. Because symptoms of mild traumatic brain injury can resemble posttraumatic stress disorder, an anxiety disorder, it can be difficult to distinguish the two.

While DTI is promising as a new diagnostic technology, Moore emphasizes that additional alternatives are still sorely in need. About 80 percent of the brain injury patients eligible for the study at Walter Reed Army Hospital had to be excluded because of metal shrapnel in their bodies. (MRI machines generate a strong magnetic field, making it dangerous for people with metal implants or shrapnel.)