Researchers in Boston recently published a fascinating paper describing the clinical and neuroanatomical findings of 202 deceased American football players who donated their brains to a brain bank. Chronic traumatic encephalopathy (CTE), a progressive degenerative disorder of the brain that is associated with repeated head trauma was diagnosed in 177 of the players (87%) across all levels of play. When looking at the rates of disorder by the highest level of play for each participant, the researchers found CTE in the donated brains of
- 110 of 111 former NFL players (99%)
- 7 of 8 Canadian Football League players (88%)
- 9 of 14 semi-professional players (64%)
- 48 of 53 college players (91%)
- 3 of 14 high school players (21%)
- 0 of 2 pre-high school players (0%)
It is important to note that this study was not designed to determine what percent of football players overall have CTE. It was designed to learn more about the brains and clinical histories of football players who had the disorder. Because people who agree to donate their brains after death may have done so because they had symptoms suggestive of CTE or were worried about having the condition, a selection bias was introduced into the sample that undoubtedly contributed to the high rates of CTE reported in this paper. Further compounding the
Bias is the fact that, starting in 2014, inclusion criteria for the brain bank was changed so that football players who died after the age of 35 had to have at least 2 years of college level play. That being said, the study is important because it is the largest case series of CTE ever reported. The findings will help us better understand the disease and also highlight areas that need more research.
How was the study conducted?
The donated brains were subjected to a standardized neuroanatomical evaluation using criteria for CTE defined by the 2015 NINDS-NBIB Consensus Conference. CTE pathology was classified into one of four stages of severity with Stage I and Stage II disease considered mild CTE and stages III and IV considered severe.
The researchers also performed a retrospective clinical evaluation of 111 CTE cases using a standardized informant report. They conducted post-mortem telephone interviews with family or friends in order to ascertain the timeline of cognitive, behavioral, mood, and motor symptoms as well as the cause of death. They also asked about PTSD, substance abuse, headaches, sleep disorder, and any neurodegenerative diagnoses that were made during the life of the player as well as any history of traumatic brain injury, including whether the person had a history of concussions. Importantly, neither the interviewer nor the informants (the people being interviewed) were aware of the neuroanatomical diagnosis at the time of the interview.
What they found
The median age at death of the 177 football players with CTE was 67 years, and the mean years of football participation were 15.1 years. Seventy-nine percent (79%) of the participants in the study were white and 19% were black. If you look at the findings based on highest level of play, participation in the National Football league was associated with the highest rate of CTE at 99% (110 out of 111 players)—the vast majority having severe disease. The majority of former college players, semi-pro, Canadian Football League players (86%) also had severe pathology. All 3 participants with CTE, whose highest level of play was only high school, had mild disease. The mean duration of play for participants with mild CTE was 13 years compared to severe with 15.8 years.
The median age of death for mild cases was 44 years old and for severe, 71. The most common cause of death for participants with mild CTE was suicide. For those with severe pathology, it was a neurodegenerative disease.
Evaluation of the primary position at the highest level of play showed that offensive linemen, defensive linemen, and running backs were more likely than tight ends, wide receivers, or kickers to have severe neuroanatomical CTE in their donated brains. Among the 25 football players without CTE, 9 showed normal brains and 7 had nonspecific changes, the remainder had a variety of other diagnoses.
Behavioral or mood symptoms were common
A hundred and eleven (111) CTE cases had standardized informant reports on clinical symptoms. A progressive clinical course was common in participants with both mild and severe CTE pathology. Behavioral or mood symptoms were also common in both mild and severe cases. Specifically, impulsivity, depressive symptoms, apathy, and anxiety were common in both mild and severe cases. In addition, symptoms of hopelessness, explosivity, being verbally violent, being physically violent, suicidality, and substance use disorders were commonly described in mild cases. PTSD symptoms were uncommon in both groups.
Cognitive symptoms were common in both mild and severe. For example, memory, executive function, and attention symptoms occurred in most mild as well as severe cases. Language and visuospatial symptoms were common in severe cases. Eighty-five percent (85%) of patients with severe CTE findings had signs of dementia as assessed by the post-mortem interviews.
Motor symptoms were common in severe cases, including slow movement and gait instability. There were no asymptomatic CTE cases.
The authors of the paper concluded that the findings
“suggest that CTE may be related to prior participation in football and that a high level of play may be related to substantial disease burden.”
The researchers also cautioned that you cannot use data from this study to estimate prevalence of CTE in football players in general or professional football players, in particular, because of the bias introduced in the design of the study: Individuals who met inclusion criteria of repetitive head trauma and a history of playing at a high level of football chose whether or not to donate their brains.
I know many may be tempted to use this study to decide whether or not they or their kids should participate in football. But the study was not designed to answer this question. Yes, there are a lot of football players, especially those with a high level of play such as the NFL, who demonstrated the brain disorder in their donated brains. But, many of those players played football decades ago when there was not as much awareness of the consequences of repetitive head trauma nor regulations and protective gear to protect against it. In addition, it is important to acknowledge that there are so many things we don’t yet know about CTE: Are there genetic predispositions? Are their correlations with age of exposure to the game? Does the head trauma need to result in concussion or are subconcussive injuries also risk factors? Until we can answer those questions, individuals and families will have to make decisions about playing football based on incomplete data. Hopefully, more research will be forthcoming soon that can help guide them in their decision-making process.