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Despite a high risk of brain injury, military personnel rarely develop chronic traumatic encephalopathy (CTE), a debilitating condition commonly found in former boxers and football players.
Less than 5% of the 225 brains of deceased servicemen showed evidence of CTE, a team reports in the June 9 issue of The New England Journal of Medicine.
In contrast, a 2017 study of brains from deceased college and NFL football players found that 87% had signs of CTE.
Even military personnel who had suffered concussions from bomb explosions were unlikely to develop CTE. Only 6.7 percent of the brains of 45 people exposed to blast were diagnosed with the condition.
The results suggest that “serving in the military and being exposed to explosions is unlikely to be a significant risk factor for developing CTE,” said Dr. Daniel Perl, a professor of pathology at Uniformed Services University in Bethesda and one of the authors of the study.
CTE cannot be diagnosed until after a person has died. During an autopsy, a pathologist looks for brain regions with high concentrations of a toxic form of the protein tau.
The condition is associated with dementia, mood problems and a range of psychiatric disorders.
The symptoms of CTE overlap with those seen in military personnel exposed to bomb attacks.
Thus, some doctors fear that CTE may be partly responsible for the high suicide rate and post-traumatic stress disorder (PTSD) among veterans who served in Iraq and Afghanistan.
“Their families said their personalities had changed, that they had trouble sleeping,” Perl says.
To see if CTE was a factor, researchers turned to the Brain Tissue Repository, which is operated by the Department of Defense and the Uniformed Services University led by Perl.
“We said this was the chance to look at that brain and see how much CTE played a role in this problem,” Perl says.
The team found that out of 10 brains with CTE, only three came from military personnel exposed to bomb attacks.
“Then we discovered they had done all ten contact sports,” says Perl.
The results add to the evidence that bomb explosions and sports effects affect the brain in different ways.
Brain injuries in football or boxing are caused by an impact that presses the brain against the skull. In a bomb explosion, a pressure wave travels through brain tissue, causing it to stretch and deform.
“The physics is different,” Perl says. “And apparently the pathology that results from it is different.”
But bumps and blasts can both do permanent damage, Perl says.
“You shouldn’t think that because we didn’t find CTE, the brain is normal,” he says. “That is clearly not the case.”
Also, most of the brains in this study came from relatively young people, Perl says. So it’s possible that more of them would have developed CTE as they got older.