AAN 2009: Imaging Study Shows Blast Injury May Cause Brain Inflammation

Caroline Cassels

May 05, 2009

May 5, 2009 (Seattle, Washington) — For the first time, a new imaging study that employs diffusion tensor imaging (DTI) shows that veterans who sustain mild traumatic brain injury (mTBI) caused by blasts have a different pattern of injury than their counterparts who suffer mTBI as a result of a direct hit to the head that does not involve an explosion.

In a presentation here at the American Academy of Neurology 61st Annual Meeting, investigators from the Defense and Veteran Brain Injury Center, in Washington, DC, found that veterans with blast-related mTBI had a diffuse pattern of injury involving more of the brain's white matter.

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Furthermore, say researchers, there were also other parameters that were "abnormal" in blast patients — specifically, the apparent diffusion coefficient (ADC), which was lower in blast-related injury, possibly indicating swelling or inflammation that is akin to what occurs in the brain with infection or stroke.

"The study essentially found the pattern on DTI in blast patients was different from the pattern seen for the traditional impact forms of TBI, which again was different from healthy controls who hadn't sustained a head injury," study investigator Col. Michael Jaffee, MD, told Medscape Neurology & Neurosurgery.

Blast Injury a Common Occurrence

Blast injuries are much more frequent in the current conflicts in Iraq and Afghanistan than they have been in other wars. Various factors, including Kevlar body armor and helmets, have made penetrating wounds — and specifically penetrating head wounds — much less common.

However, the widespread use by insurgents of improvised explosive devices (IEDs), also known as roadside bombs, in the current conflicts is contributing to an unprecedented number of concussive closed head injuries.

A position paper published in 2008 by the Brain Injury Association of America estimated that as of March 24, 2007, a total of 12,274 US service members had sustained a TBI in either Iraq or Afghanistan but projected this number "could grow as high as 150,000."

Other estimates assert that 22% of all returning service personnel have some form of TBI, 69% of whom were injured by IEDs, rocket-propelled grenades, and other blasts. TBI screening, which began in August 2007 at the National Naval Medical Center, showed 83% of wounded Marines and sailors had brain injuries.

Yet, despite the fact that it is a common occurrence, the study's principal investigator, David F. Moore, MD, PhD, said relatively little is known about the effects of blast injury.

"Whether blast injury might actually cause an augmentation of 'normal' or impact-related head injury is not clear, and this has important implications for service members in terms of their return to duty status, their overall health, and their readiness to undertake their mission," Dr. Moore told Medscape Neurology & Neurosurgery.

Persistent Complaints

Dr. Jaffee agreed, adding that understanding blast injury and how it compares with impact-related head injury has been one of the biggest medical challenges of the current conflicts.

"We've really been trying to better understand the pathophysiology [of blast injury], how it affects the brain and how we can better diagnose it," he said.

Difficulties experienced as a result of mTBI can be divided into symptom clusters that include cognitive effects such as short-term memory and attention problems; emotional symptoms such as irritability, depression, and anxiety as well as possible symptoms of posttraumatic stress disorder (PTSD); and physical sequelae including headache, dizziness, insomnia, and decreased energy.

In the majority of mTBI cases, symptoms resolve within a matter of days or weeks. However, said Dr. Jaffee the study findings may be particularly important for the minority of patients with persistent complaints.

"We need to better understand what is going on with this group of patients. If they are able to get a DTI study it may provide clarification about whether blast is a contributing component to their symptoms and have implications for treatment as well as prognosis," Dr. Jaffee said.

Need for Objective Measures

Using traditional structural brain-imaging studies such as magnetic resonance imaging (MRI) or computed tomography (CT) scans to detect and diagnose mTBI often reveal normal results.

"At the end of the day, there's still a reliance on history and clinical determination based on history from the patient or history from witnesses. What is needed is a more objective measure that can help guide us in the diagnosis and treatment," said Dr. Jaffee.

The emergence of DTI, a relatively new MRI technique that highlights white-matter tracts vs gray matter, gives researchers a much better understanding of white-matter bundles, which are responsible for forming direct connections between distant regions in the brain.

This technology has already been used in previous research to identify neuroimaging markers of impact-related head injury. However, said Dr. Jaffee, the current study is the first to use DTI to examine patients who have had blast as a component of their head injury.

The case-control study compared DTI scans of military service members with documented mTBI, with and without loss of consciousness, associated with blast (n = 29), impact-only mTBI (n = 10), and healthy military controls (n = 12) with no history of TBI or neuroradiological abnormalities.

DTI parameters included ADC and fractional anisotropy (FA) in the anterior-posterior, superior-inferior, and right-left directions.

Insight into Pathophysiology

According to the investigators, individuals with blast mTBI had significantly decreased FA compared with the control group that showed up on imaging as a "salt-and-pepper"–type distribution in the brain's white matter. On the basis of animal studies, this "diffuse" pattern was not unexpected.

However, Drs. Moore and Jaffee said it was surprising that ADC decreased, suggesting blast-injury may produce inflammation in the brain. This finding, said Dr. Jaffee, sheds light on the pathophysiology of blast injury and may have future implications for diagnosis and treatment.

"We in the Defense and Veterans Brain Injury Center and the Department of Defense are always committed to further scientific understanding that will allow us to apply the best evidence and the latest science to advance the best care of our service members who put themselves in harm's way," he said.

Dr. Jaffee added that DTI is 1 example of an imaging parameter that can provide objective measures of brain injury. Another, he said, is the development of helmet detectors that service members would wear to provide another potential source of objective information to help guide diagnosis.

The authors report no conflicts of interest.

American Academy of Neurology 61st Annual Meeting: Abstract LBS.002. Presented April 29, 2009.

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