A small scientific study of veterans exposed to bomb blasts while serving in Iraq and Afghanistan uncovered signs of lasting brain damage even in cases where there were no outward symptoms such as headaches, dizziness or confusion.
Even though a soldier may not appear hurt by a blast wave doesn't mean there aren't small changes to the brain, concludes the report published Monday in The Journal of Head Trauma Rehabilitation.
The authors cautioned that it remains unclear whether those changes will alter how the service member functions in the long run.
"There are clearly questions that we need to follow-up on," says Katherine Taber, a Department of Veterans Affairs scientist and lead author.
But scientists also found the results troubling because they suggest untold numbers of undiagnosed traumatic brain injury or TBI among U.S. service members, thousands of whom were routinely caught near roadside bombs blasts while on combat patrols.
"A lot of these military guys will not have had symptoms, like feeling dazed or confused, but yet they may have (brain) damage," says Rajendra A. Morey, a co-author and psychiatrist at Duke University School of Medicine.
A RAND Corp. study in 2008 estimated that IED blast events were so frequent that perhaps 320,000 troops may have suffered mild TBI.
Authors of the study say the best way to confirm changes in the brain after a bomb goes off is using advanced imaging machines that can "look below the surface" for problems.
Without that, there may be the "erroneous assumption that there has been little or no effect on the central nervous system," the report says.
The military deployed three advanced imaging machines to the Afghanistan in late 2011 to assist doctors in treating mild brain injury. Magnetic resonance imaging or MRI machines had the same power as devices used in the study. But medical leaders concluded the war-zone MRI's were not effective and ordered them dismantled last year.
The study funded by the Pentagon and VA, collected data from 2006-2009 on 45 Iraq and Afghanistan veterans, including those who had symptoms following a bomb blast and those who had not.
"It was a surprise to find relatively similar (brain imaging ) changes in both groups," Taber says.
She said questions remain about what this means long-term.
Other research has suggested multiple mild-brain injuries from repeated exposure to blast could be linked with early signs of mental aging or, in a few of the worst cases, severe brain illnesses with chronic deterioration.