Mike Webster was the first.

The Pro Football Hall of Fame center for the Pittsburgh Steelers died in 2002. During an autopsy on Webster’s body, forensic pathologist Bennet Omalu identified a new kind of brain injury he coined chronic traumatic encephalopathy, or CTE.

In the years since, Omalu’s work, and the NFL’s attempts to discount it, have been the subject of a major film. That work has also led to more research and study, the results of which have shaken the world of football. A landmark 2017 study by Boston University researchers found that the brains of 110 of 111 deceased NFL players they examined showed signs of CTE. Tthese brains were likely donated by families of players who had exhibited neurologic and psychiatric symptoms, this skewing the sample.

The revelations of the past several years have brought the NFL into awareness of the problem its sport faces. Several players have retired early, fearful that the brutal sport will leave them with the irreversible brain damage CTE causes.

Others, like former Kansas City Chiefs running back Larry Johnson, wonder if their mood swings, self-destructive behavior, and memory loss are because of CTE. Johnson, who retired in 2011, told The Washington Post in December that he cannot remember two full seasons of his NFL career and that he regularly battles impulses to harm himself.

Chronic traumatic encephalopathy is a neurodegenerative disease. Over time, it causes nerve cells in the brain and parts of the nervous system to deteriorate and die. “CTE is unique but not unlike other neurodegenerative diseases such as Parkinson’s disease and Alzheimer’s disease,” says Jesse Mez, MD, an assistant professor of neurology at Boston University’s CTE Center.

Experts believe that repetitive brain trauma, or blows to the head over and over again, causes CTE, in part because such trauma leads to the harmful buildup of a protein in the brain called tau.

“In our case studies, we have not seen cases of CTE without exposure to repetitive head impacts,” says Mez.

One type of brain trauma caused by head impacts is concussion, a mild form of brain injury that can cause confusion, blurred vision, nausea, headaches, and other symptoms that usually go away within a short amount of time. Less severe hits to the head also may contribute to CTE.

People who play contact sports like football and boxing appear to be more likely to get CTE because blows to the head happen often in such sports. And such injuries are becoming more common. In recent years, the number of traumatic brain injuries in sports and other recreational activities seen in the ER has increased by more than 50% among children, according to the CDC. But during this same time, hospitalizations and death rates have slightly decreased.

Something that appears to raise players’ chances of having CTE:

How long they play contact sports. The longer an athlete’s career, the more likely they are to get CTE and the more severe that CTE may be.

However, much remains unknown, says Mez. Scientists can’t say how many hits it takes to cause CTE or how long someone must play before the risk becomes serious. In fact, different people respond differently to head trauma, he says.

“In two people who had the same amount of exposure to football, one may develop the disease and another may not, or one may have severe disease and one may have mild disease,” he says. “That suggests that there are other risk factors, like genetics.”

Symptoms which have been associated with CTE, which are similar to other neurodegenerative diseases include:

  • Loss of memory
  • Confusion and flawed judgment
  • Changes in mood, personality, and behavior, which can include depression, anxiety, suicidal thoughts and actions, and aggression
  • Dementia, in the disease’s later stages

Symptoms of CTE often begin long after the person with the disease last had a blow to the head.

Right now, CTE can only be diagnosed by examining the brain after death. But, says Mez, “we’re working really hard to come up with criteria to diagnose it in life.”

He says doctors likely will look at several things to make a diagnosis:

  • The presence of a biomarker, or physical substance in the body, that indicates CTE. No such biomarker has been identified.
  • A clinical history of symptoms
  • Repeated hits to the head

It's not reversible or curable. Mez says there can be no therapies to treat CTE until it can be diagnosed in living patients. However, some of the symptoms can be treated. For example, behavioral therapies can help treat mood changes.

Mez says that because CTE shares many traits of Alzheimer’s and other neurodegenerative diseases, it may respond to treatments for such conditions. But, he cautions, “we haven’t had a lot of success with treating Alzheimer’s, and we know a whole lot more about that disease. … I think we’re some time away from therapies.”

Football, hockey, boxing, soccer, and rugby are among the contact sports that make players most likely to have CTE. Members of the military also have a higher chance of having it. But, says Mez, statistics are scarce: “We really don’t have a sense of the incidence or prevalence of this disease at all.”

That said, CTE may be quite common among NFL players. Researchers at Boston University’s CTE Center studied the brains of 111 former NFL players. In a July 2017 study published in JAMA, they revealed that 110 -- or 99% -- of those brains tested positive for CTE.

Mez, the lead author of the study, says he knows the study had shortcomings. For example, brains donated for research were more likely to come from families of players who had shown symptoms of CTE, rather than from a wider group of players. That limited the researchers' ability to tell how common the disease is among pro football players. But the study, which also found very high levels of CTE among former college football players, was alarming.

The NFL, which had disputed the link between football and brain damage, supports efforts to protect its players from CTE and other injuries. The league recently contributed $40 million toward medical research, with a focus on neuroscience, says Allen Sills, MD, who was named the NFL’s first chief medical officer in March 2017. The neurologist and sports doctor formerly co-directed Vanderbilt University’s Concussion Center and served there as a professor of neurological surgery.

Agreeing that there's a need for more research into CTE, concussions, and related issues, Sills says, “the NFL has been a leader on safety and has made real strides to try to better protect its players and make our game safer.”

He outlines several steps the league supports, including:

  • “Data-driven” rule changes to end dangerous game tactics and make injuries less likely
  • New guidelines, medical support, and technology to identify, diagnose, and treat concussions and other injuries
  • Mandatory health and safety education for players and training for medical personnel

New rules for protective equipment

One thing that makes CTE unlike other neurodegenerative diseases, says Mez, is its clear link to “environmental exposures.” In other words, the likely cause -- repeated blows to the head over time -- is both known and preventable. For Mez, that means rethinking how we play sports.

“There are plenty of ways to play team sports and get cardiovascular exercise short of hitting your head repeatedly,” he says. “Should youths be playing contact sports? Should adults be playing contact sports? Those are really important societal questions that we should be asking.”

Some researchers say that future drugs may halt the CTE-related buildup of tau proteins in the brain caused by repeated blows to the head. While drugs that target such proteins are being developed, none have been effective.

In addition to coming up with diagnostic tests for people living with CTE and therapies to treat the disease, Mez says it’s crucial to identify who is most likely to get CTE. Genetics likely plays a role in that.

Some research now focuses on whether an Alzheimer’s-related gene, APOE-4, impacts CTE as well. Scientists also are looking at how certain genes may make a person more liable to get a buildup of tau proteins in the brain, an indicator of CTE and other neurodegenerative disorders.

The number of people over the age of 6 playing tackle football in the US has dropped by about 60% since 2006.

Some NFL players have spoken out about CTE and related issues, like concussions. In December 2017, Washington Redskins quarterback Kirk Cousins told Sports Illustrated that he would take a test for CTE if one is created. Cousins and Seattle Seahawks defensive end Michael Bennett told SI that they would retire if they tested positive. In the same roundtable discussion, Artie Burns, a Pittsburgh Steelers cornerback, said he thinks he has CTE already: “I definitely know I have it … I don’t need a test. … Humans are not made to run into each other.”

Some NFL players, such as John Urschel, A. J. Tarpley, and Chris Borland, have retired early over concerns about brain injuries.

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