FRIDAY, June 10, 2022 (HealthDay News) -- A degenerative brain condition uncovered in some former professional athletes has been reported in military veterans as well, but a new study suggests it's uncommon and questions whether service itself confers the risk.
At issue is a condition called chronic traumatic encephalopathy (CTE), a form of progressive brain degeneration believed to be caused by repeated impacts to the head over the course of years.
CTE has most famously been identified in some former pro football players, including Frank Gifford and Junior Seau, through brain autopsies performed after their deaths.
But researchers have also detected CTE in brain autopsies from athletes who played other contact sports, like hockey and boxing, as well as some military veterans.
The question of whether military service, per se, increases the risk of CTE is particularly pressing for post-9/11 veterans, said senior researcher Dr. Daniel Perl.
Those who served in Afghanistan and Iraq have had heavier exposure to "blasts," from sources like roadside bombs, versus veterans of prior conflicts, said Perl, from the Uniformed Services University, in Bethesda, Md.
Those kinds of blast waves can jar the brain without any direct blow to the head. The full consequences of those impacts are not yet clear, but studies have shown that veterans with blast exposure often have persistent symptoms — ranging from headaches, memory loss and poor sleep to depression and post-traumatic stress disorder (PTSD).
Such symptoms overlap with many of those linked to CTE — raising questions about how the brain condition fits into the picture.
For the new study, published June 9 in the New England Journal of Medicine, Perl's team examined the brains of 225 deceased service members. All tissue had been donated to a brain bank run by Uniformed Services University and the Department of Defense.
Overall, the researchers found evidence of CTE in 10 brains, or about 4%.
By comparison, a 2017 study of former football players (largely professional and college) found CTE in nearly all of the 202 brains studied.
And in this study, Perl's team found, all CTE cases occurred in veterans with a history of playing contact sports — mostly football and/or combat sports (such as boxing and wrestling).
Contact sports did, in fact, show the strongest link to CTE. Of the 60 veterans who'd played, 10 had evidence of CTE in the brain; that compared with none of 165 veterans with no history of contact sports.
The researchers were able to examine the brains of 45 veterans who'd had blast exposures during their service. Three of those brains (almost 7%) had CTE, versus seven of 180 brains (4%) from veterans with no history of blast exposure — a difference that was not statistically significant.
And again, Perl said, all of those veterans with CTE had a history of contact sports, and often had sustained concussions in civilian life that were not related to sports, too — from traffic accidents, falls or fights.
Service members are, on the whole, a "rough-and-tumble" crowd, Perl explained, which makes it more difficult to ascribe CTE to blast exposure.
Another difficulty, according to Perl, is that the prevalence of CTE in the general population is unknown, so no comparison can be made. (At this point, CTE can only be diagnosed through brain autopsy.)
However, a CTE researcher who reviewed the study said it does not refute the link between blast exposure and CTE: It was simply unable to show a statistically significant association due to the small number of cases.
Ten years ago, Dr. Lee Goldstein and his colleagues reported the first case series of military veterans with blast exposure and CTE. Those four vets, who were an average age of 32 when they died, showed "exactly the same lesions" as seen in the brains of four young contact-sport athletes, Goldstein said.
Then, in experiments with mice, the researchers showed that a single blast exposure caused CTE-like brain changes within a couple weeks, along with memory and learning impairments.
Goldstein, of Boston University's CTE Center, said the condition stems from repetitive impacts to the head — including those that do not actually cause a concussion.
"It's not about concussion. It's the repeated injection of damaging energy into the brain," Goldstein explained.
And a single blast exposure, he said, is like receiving multiple impacts compressed within milliseconds. "It's a very efficient way to deposit damaging energy into the brain," Goldstein said.
In the latest study, most of the 10 veterans with CTE lesions died young, between the ages of 30 and 60. Many had been diagnosed with PTSD, depression or a substance abuse disorder, and four had died of suicide.
However, the researchers said, it was not clear whether CTE preceded those diagnoses. And those conditions, as well as suicide, were also unfortunately common among veterans who died with no evidence of CTE.
To Perl, the findings suggest that CTE does not explain the persistent neurological and psychiatric symptoms among service members with blast injuries.
"To try to explain these symptoms as either CTE or a mental health issue would be incorrect," Perl said. "We need more research to understand the biology."
He acknowledged the limitations of the study, too. One is that the veterans typically died young — at age 48, on average. It's possible the rate of CTE among blast-exposed veterans could be higher at older ages, Perl said.
For now, Goldstein encouraged veterans and active service members to seek help for depression, PTSD or other persistent symptoms causing them "distress." Whatever the underlying biology, he said the symptoms need to be taken seriously.
The U.S. Centers for Disease Control and Prevention has more on CTE.
SOURCES: Daniel Perl, MD, professor, department of pathology, Uniformed Services University, Bethesda, Md.; Lee Goldstein, MD, PhD, associate professor, psychiatry, Boston University School of Medicine, Boston; New England Journal of Medicine, June 9, 2022