Boston University has found Chronic Traumatic Encephalopathy (CTE), a degenerative brain disease that has been linked to repetitive brain injuries, in the brains of 345 out of 376, or 92%, of former NFL players studied. While this is a striking and concerning number, it does not mean that 92% of all former NFL players have this disease. Let’s put this finding in context and discuss what it means for all contact sport athletes today.
What is CTE?
CTE is a degenerative brain disease that has been linked to exposure to repetitive brain trauma. That brain trauma can include both concussions and repetitive “subconcussive” impacts. The disease has been diagnosed in some individuals with no documented concussions but a history of repetitive head impacts that do not result in symptoms. Those repetitive impacts can occur on every play in many sports, including every tackle or collision between linemen in football, every check in hockey, and every header in soccer.
CTE has been diagnosed in individuals with a variety of exposure to repetitive brain trauma, including football, soccer, hockey, and rugby athletes, as well as military veterans and victims of domestic violence. CTE symptoms often begin in middle-age, sometimes years after the last exposure to brain trauma, and can include cognitive difficulties, memory loss, behavioral difficulties, impulsivity, and depression, among other symptoms.
At this time CTE cannot be diagnosed during life. It can only be diagnosed by postmortem examination of the brain. Generous donors and their families have donated their brain to brain banks studying the disease, such as the Boston University/Concussion Legacy Foundation Brain Bank, after they pass away. This incredibly gift from donors has lead to breakthroughs in research about the long-term consequences of repetitive brain trauma in sports, the military, and beyond.
Do 92% of NFL players have CTE?
The answer is almost certainly “no.” Brain banks have a selection bias. The sample they study is not random. Most players or their families don't think to donate their or their loved one's brain unless they think they have the disease. As a result, it is not surprising that many of the donors had CTE.
It is highly unlikely that ever other former NFL player that passed away during the same time period as those studied at Boston University had CTE. Thus, it is unlikely that 92% of all NFL players have the disease.
Despite the bias, the prevalence of CTE in NFL players is still likely high. After previous research showed 110 of 111 former NFLers examined had CTE, a study found that, if it is assumed that all other players who passed away in the same time period did NOT have CTE, the minimum prevalence rate would be 9.6%. That is about one in ten players, or about 5 players on every active NFL roster.
It is highly likely that some of the former players who passed away but were not studied did have CTE but were not diagnosed, making that prevalence even higher.
What does this mean for most current or former contact sport athletes?
We don’t know the true prevalence of CTE in the NFL population or in any contact sport athletes at any level. There is evidence that the risk for developing CTE increases with a greater number of repetitive head impacts over a lifetime. In one study, those who played tackle football for 14 years or more were ten times more likely to develop CTE, while those who played tackle football for 4 years or less were ten times less likely to develop the disease.
Still, there are cases of athletes who played contact sports only through the high school level that developed CTE. The youngest documented case I am aware of was in a 17-year-old. While the prevalence at this level is likely low, there is still risk.
For those who are concerned that they may have CTE based on their athletic history and current symptoms, CTE symptoms are not unique to CTE. Depression, certain cognitive difficulties, and anxiety, for example, can have many causes, and these symptoms can be treated.
As Dr. Ann McKee said in a Boston.com article:
“While the most tragic outcomes in individuals with CTE grab headlines, we want to remind people at risk for CTE that those experiences are in the minority,” Ann McKee, director of the BU CTE Center and chief of neuropathology at VA Boston Healthcare System, said in a statement. “Your symptoms, whether or not they are related to CTE, likely can be treated, and you should seek medical care. Our clinical team has had success treating former football players with mid-life mental health and other symptoms.”
If you are concerned that you or a loved one may have symptoms that may be related to CTE or previous concussions, you can contact the Concussion Legacy Foundation HelpLine. The Concussion Legacy Foundation has many resources available about CTE, Concussions, and Post-concussion syndrome. The HelpLine can provide referrals, online support groups, one-on-one peer support, and other resources.