Too little is known about how or whether bomb blasts cause long-term damage to the human brain and body, according to a scientific panel focusing on wounds caused by roadside bombs, the most common enemy weapon used in Iraq and Afghanistan.
While the long-term effects of certain blast-related wounds are obvious – such as amputated arms or legs – what isn't understood are the chronic risks of unseen damage from the blast wave, the Institute of Medicine panel concludes in its report issued Thursday.
The question is crucial because of potentially tens of thousands of American troops caught near blasts during a dozen years of combat in Iraq and Afghanistan.
"If someone is exposed (to a blast) and outwardly looks all right, what we don't know is whether that blast is doing something to their brain, to their heart, to their lungs, to their liver, that is going to cause a problem down the line," says Jeffrey Bazarian, a panelist and associate professor at the University of Rochester School Medicine and Dentistry
The committee cited military records showing 3,589 U.S. troops killed by roadside bombs in Iraq and Afghanistan and another 32,556 wounded. But there are also gaps in medical records that make it difficult to know precisely how many health problems troops or veterans have that are linked to the blasts, the scientific committee found.
"It is likely that many others are exposed to blasts in the combat environment but do not require immediate medical attention and, therefore, are not reflected in the numbers reported," the committee report says.
The Institute study was done at the request of the Department of Veterans Affairs, which must care for wounded veterans of Iraq and Afghanistan. About 2.6 million Americans deployed to both wars, and more than 1.7 million are now veterans.
About 1 million have sought medical care from the VA, nearly 300,000 of them for post-traumatic stress disorder, a disease the scientific panel says can be associated with surviving a roadside bomb attack or witnessing its aftermath.
About 32,000 Iraq and Afghanistan veterans have been diagnosed with brain damage, according to the VA.
One encouraging development has been research launched by the VA that Bazarian says could fill many of the knowledge gaps in blast-related injuries. Markers in the blood or better imaging machines can also assist in identifying what are now too often hidden or invisible damage caused by blast waves, the committee said.
The risk of hidden damage from blast exposure was rarely considered by military medical doctors during the first several years of fighting in Iraq and Afghanistan. Troops caught near a roadside bomb explosion who were not bleeding or unconscious often were sent back into combat despite symptoms such as dizziness or headaches.
The result: uncounted numbers of troops who were then exposed to a second or third blast before brain damage from the first had time to heal.
The scientific panel found research that established a limited association between repeated bomb-blast exposures and chronic traumatic encephalopathy, a long-term degenerative brain disease similar to Alzeheimer's.
Other evidence suggests that damage from a blast wave can be more widespread across the brain than damage caused by blunt-trauma such as a blow to the head.
More research is needed, the committee says.
"Filling the gaps (in knowledge) is important for advancing the understanding of how blast affects humans in the short term and the long term," the committee report says.
Currently, soldiers who are exposed to bomb blasts are more aggressively questioned about symptoms and are pulled from combat until those symptoms go away.
But the committee warned that there is still so much mystery about the wound that there could be damage even without any outward signs.
"Such servicemembers, in practice in the battlefield, would be indistinguishable from the uninjured," the panel says. " The committee believes that it would be an error...to assume that long-term consequences can occur only as a result of clinically detected initial (obvious) injuries caused by blast exposures."