Do Concussions Cause CTE? Sports Doctors and Scientists Disagree.

AMSTERDAM — For the first time since 2016, one of the most influential groups guiding doctors, trainers and sports leagues on concussions met last month to decide, among other things, if it was time to recognize the causal relationship between repeated head hits and the degenerative brain disease known as C.T.E.

Despite mounting evidence and a highly regarded U.S. government agency recently acknowledging the link, the group all but decided it was not. Leaders of the International Consensus Conference on Concussion in Sport, meeting in Amsterdam, signaled that it would continue its long practice of casting doubt on the connection between the ravages of head trauma and sports.

C.T.E., or chronic traumatic encephalopathy, was first identified in boxers in 1928 and burst into prominence in 2005, when scientists published their posthumous diagnosis of the disease in the N.F.L. Hall of Fame center Mike Webster, creating an existential crisis for sports such as football and rugby that involve players hitting their heads thousands of times a year.

Scientists have spent the past decade analyzing hundreds of brains from athletes and military veterans, and the variable evident in nearly every case of C.T.E. has been their exposure to repeated head trauma. Researchers have also established what they call a dose response between the severity of the C.T.E. and the number of years playing collision sports.

After playing down an association between head injuries and brain damage for years, the N.F.L. in 2016 acknowledged that there was a link between football and degenerative brain disorders such as C.T.E. Just days before the conference in Amsterdam, the National Institutes of Health, the biggest funder of brain research in the United States, said that C.T.E. “is caused in part by repeated traumatic brain injuries.”

But in one of the final sessions of the three-day conference, one of the leaders of the conference, a neuropsychologist who has received $1.5 million in research funding from the N.F.L., dismissed the work of scientists who have documented C.T.E. in hundreds of athletes and soldiers because he said their studies thus far did not account for other health variables, including heart disease, diabetes and substance abuse.

“To think that there is one factor that is contributing to their current problems and that factor you can see under a microscope after death is an extraordinarily naïve position when you think about the human condition,” said Dr. Grant Iverson, a neuropsychologist at Harvard who ran the session and was a lead writer of the conference’s statement on long-term impacts of repeated head trauma.

A recording of that session obtained by The New York Times, as well as interviews with people who attended, offered a rare glimpse of the fissures among the scientists who set concussion policy in sport, and it revealed reasons for their continued refusal to consider almost all of the new research on long-term impacts of head trauma as they prepare to release guidance for sports leagues around the world.

At the heart of the group’s purpose is its consensus statement, periodically issued concussions guidance agreed upon by most of group’s several dozen members. It is foundational to the protocols of many of the world’s top pro-sports leagues. Medical advisers to many of those leagues, including the chief medical officers for the N.C.A.A. and World Rugby, helped craft that statement in Amsterdam. The newest iteration was expected to be released in 2023.

But the makeup of the group itself poses apparent conflicts of interest that call into question their delay on accepting new research on concussions. FIFA; the I.O.C.; the F.I.A., which governs automobile racing leagues including Formula One; World Rugby; and other governing organizations in sports sponsor the conference and have working relationships with many of the leaders of the conference or provide them with research funding.

“This group has been led by people who don’t really have a full understanding of the pathology of head injury at that level,” said Willie Stewart, a neuropathologist in Glasgow who has diagnosed C.T.E. in many athletes. He said the conference leaders should have their terms limited. “There should be a rotation of people so they don’t have any fear of what they said four years ago.”

Previous consensus statements claimed that the science was not settled on C.T.E., and that language has been adopted by sports leagues including the N.H.L., the N.C.A.A. and New Zealand Rugby, a stamp of approval from scientists that has helped some of those organizations fend off lawsuits accusing them of hiding the dangers of concussions from athletes.

Still, researchers pushing for a recognition of a cause-and-effect relationship between head trauma and C.T.E. were initially optimistic that the group’s leaders might be swayed by new research. In March, Paul McCrory, a longtime leader of the group and a vocal skeptic of the links between head hits and C.T.E., resigned after he was caught plagiarizing.

But in conversations before and during the conference, leaders of the group centered their discussions on what was unknown about C.T.E., noting that it was unclear why some athletes got the disease and others who played the same sport did not. No one can say how much head trauma is needed to get C.T.E. A reliable test for diagnosing the disease in the living is at least five years off, experts said.

Then, in one of the conference’s final sessions, titled “Long Term Sequellae and Criteria for Retirement,” Iverson began the hourlong confab by discussing the criteria the group would use to review concussions research.

Of the nearly 7,500 papers on concussions that the group identified, the writers of the consensus statement considered just 26, which did not include any of the major research papers on C.T.E. Dr. Ann McKee, a neuropathologist at Boston University who is the world’s leading C.T.E. expert, pulled out of the conference because she was told her work would not be fully integrated into the statement.

Jon Patricios, Bob Cantu, Mike McNamee and Kathryn Schneider, the leaders of the conference, said in an email that some research on C.T.E. that was excluded from the formal review was still presented at the session so that “a spectrum of views” could be heard. They added that they were unable to share specifics on which were included.

Iverson described the limitations of the existing research and why much of it was excluded from consideration. Most C.T.E. research, he explained, considered only one or two variables, like age and sex, but not others, like heart disease, diabetes and alcohol abuse.

Because the disease can only be diagnosed posthumously, scientists have not yet created long-term studies which follow living subjects through their lives as some are exposed to brain trauma and others are not. In that scenario, scientists would need to solicit brains from people who did not compete in collision sports and would not know the results of the study until after the participants had died.

“If we think about the importance of later-in-life brain health, these are some variables that are important to consider,” Iverson said.

Some who attended the session were unconvinced that the lack of such research mitigated the avalanche of studies that establish a causal relationship between brain trauma and C.T.E.

“To do the types of studies they want to include in this way will take decades,” said Michael Grey, who teaches rehabilitation neuroscience at the University of East Anglia in England. “Are we supposed to wait decades and have tens of thousands of people suffer from neurodegeneration when we could be doing something about it now?”

A conference rule allows just 7 of the 29 writers to block language in the statement, potentially creating another barrier to the group agreeing to phrasing that links head trauma to C.T.E. The consensus-statement writers include many doctors who do not specialize in degenerative brain disease yet advise the N.H.L., Australian Football League and other leagues.

Cantu, one of the foremost researchers on C.T.E., followed Iverson with a 15-minute presentation in which he told the group that it had “kicked down the road” the issue of C.T.E. in their last two consensus statements, published in 2013 and 2017. He said that the cognitive, behavioral and mood issues associated with C.T.E. overlap with many other diseases, which make it hard to diagnose clinically.

But since 2016, he said there have been more than 100 papers a year published on C.T.E., including one he co-wrote this year with Chris Nowinski, a Ph.D. in behavioral neuroscience who co-founded the nonprofit Concussion Legacy Foundation, and other researchers. In it, they detailed their findings that there existed a high probability that repeated head trauma causes C.T.E. Their paper, he said, helped convince the N.I.H. to change its stance.

Nowinski and his colleague from the Concussion Legacy Foundation, Adam White, taunted the leaders of the conference by holding satirical drawings as they arrived.

Credit…Adam White

Their posters featured smiling doctors in lab coats holding cigarettes, with “Enjoy repetitive head impacts” and “Don’t worry about CTE!” a parody of advertising in the 1940s and 1950s in which doctors promoted smoking.

“I’m there to remind them that if they don’t acknowledge a cause-and-effect relationship, a lot more people are going to get hurt and it’s going to ruin their reputations,” Nowinski said. “The problem is, if they say cause-and-effect is established, it will cost the organizers of the conference a lot of money in lawsuits.”

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