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A generation of Iraq and Afghanistan veterans exposed to explosions may be at risk for early-onset dementia, according to a new study that looked at the autopsied brains of four former combat service members and four athletes.
Scientists said their work showed evidence of a progressive degenerative brain disorder known as chronic traumatic encephalopathy (CTE), a disease found in recent years among deceased professional football players who had suffered multiple concussions.
What researchers said was particularly alarming was evidence that the disorder could result from exposure to a single blast and that several hundred thousand U.S. troops may have suffered concussions in Iraq and Afghanistan, most of them from exposure to explosions.
"Ramifications are that these hundreds of thousands of military personnel are at risk for this disorder. It doesn't mean by any means that they all have or will get it. But they are at risk for it," said Ann McKee, a Department of Veterans Affairs scientist and co-author of the study in Science Translational Medicine.
The study findings were based on comparing brain autopsies of four Iraq and Afghanistan veterans with four young athletes, as well as studying mice exposed to a simulated blast.
Army and Navy brain-trauma scientists who treat or study soldiers and Marines who suffer combat brain injuries applauded the study for focusing attention on CTE, but questioned some of the conclusions.
Given the limited number of brain autopsies performed in the study, Army Col. Geoffrey Ling cautioned against sweeping conclusions about risks to veterans in the future. Navy Cmdr. Jack Tsao noted that most of the deceased veterans had also suffered concussions from blows to the head, calling into question whether blast exposure was the true cause of long-term damage.
Daniel Perl, professor of pathology and a neuropathologist at the Uniformed Services University of the Health Sciences, says the findings will certainly spur more research. "It's not the whole story. It's just the beginning, and it raises a whole number of additional questions that will need to be answered. But it is important," said Perl, who is creating a lab to study the brains of deceased troops who suffered combat concussions.
Progression of CTE — marked by memory loss, suicidal thoughts and aggression — is slow, but appears irreversible after eight to 10 years, with the prospect of early dementia within a few decades, the scientists said.
"We need to find some answers quickly so that we can treat veterans, military personnel, before anything gets worse," said Lee Goldstein, a scientist with Boston University and lead author of the study.
The average age of the four veterans whose brains were autopsied was 32. All showed signs of CTE, the study says.
Two died of burst blood vessels in the brain, one from a pain medication overdose and the fourth from suspected suicide. Three had mild traumatic brain injuries from roadside bomb blasts, and one had several concussions, but none caused by a blast.
To support their autopsy findings, researchers studied the effects of a single blast on the brains of mice. The study of mice exposed to a simulated blast led McKee and Goldstein to conclude that supersonic blast waves caused by expanding gas from a detonation can lead to brain injury.
A "blast wind" of 330 mph whips the brain about violently, damaging cells and blood vessels and triggering a cascade of events that lead to a destructive buildup of a tau protein in the brain — evidence of CTE. "You may be getting in one blast exposure the equivalent of multiple hits on the playing field," Goldstein said.