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July 27, 2017

Nearly all NFL players studied had degenerative brain disease, researchers say

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    A majority of professional football players who demonstrated behavioral symptoms of chronic traumatic encephalopathy (CTE)—thought to be caused by repeated head injury—had the brain disease, according to new research published Tuesday in JAMA.

    Learn how 4 progressive providers are managing concussion care

    The study follows the National Football League's public acknowledgement last year of a connection between football-related head injuries and CTE. Prior to that acknowledgement, the NFL had responded vaguely to questions about the link.

    What is CTE?

    CTE is a brain disease that currently can be diagnosed only by examining the brain tissue of deceased subjects. However, scientists say people who are diagnosed with the disease post-mortem can present with symptoms while they are living such as aggression, anxiety, confusion, dementia, depression, memory loss, and substance use. There is no known treatment.

    Many scientists theorize that repeated head trauma causes CTE, which is correlated to deteriorated brain matter and the abnormal accumulation of tau, a protein, the Associated Press reports. Those at highest risk for CTE include combat veterans and athletes in contact sports, such as football.

    According to the AP, researchers are investigating methods that could be used to assess people while they are alive.


    For the study, the researchers examined 202 brains from deceased football players, according to the Los Angeles Times' "Science Now." The sample included professional athletes from the National Football League (NFL) and the Canadian Football League (CFL), as well as semiprofessional athletes and athletes who had not gone professional but played during college or high school.

    However, the researchers said the brains were a "convenience sample"—while athletes in some cases decided to donate their brain tissue after death, most of the tissue was donated by the family members of athletes who had shown signs of CTE while living. In addition, according to the researchers, much of the donated brain tissue came from subjects who had played football long-term—from youth and well into their 20s.

    The researchers added that they did not compare their sample to the brain tissue of randomly selected former football players, or against the brain tissue of players who had shown no signs of the disease while living.

    Lead researcher Ann McKee, chief of neuropathology at the VA Boston Healthcare System and director of the CTE Center at Boston University, said the diagnoses were made based on recent criteria from the National Institute of Neurological Disorders and Stroke.


    The researchers found "clear evidence" of CTE in 87.6 percent, or 177, of the brains examined. According to the researchers, those 177 athletes had on average played football for 15 years.

    Looking at the different groups of football players, the researchers diagnosed CTE in the brains of:

    • 110 of 111 former NFL players;
    • Seven of eight former CFL players;
    • Nine of 14 former semi-professional players;
    • 48 of 53 former college players; and
    • Three of 14 former high school players.

    Neither of the two brains donated from individuals who stopped playing football before high school had the disease, the researchers said.

    Of the 177 players whose brain tissue indicated CTE:

    • 91 percent had behavioral or mood symptoms while living;
    • 86 percent had memory problems while living;
    • 72 percent had dementia in their last year of life; and
    • 68 percent had motor symptoms while living.

    The researchers classified the brains with evidence of CTE as having either "mild" or "severe" pathology. They found severe pathology in 133 of the 177 cases and mild pathology in 44. Those with severe pathology had played football for an average of 15.8 years, while those with mild had played for an average of 14 years.

    Further, when assessing the cause of death, the researchers found that:

    • Suicide was the most common cause of death among those with mild CTE, accounting for 27 percent of fatalities in that group; and
    • Degenerative diseases such as Alzheimer's and Parkinson's disease were the most common causes of death among those with severe CTE, accounting for 47 percent of fatalities in that group.

    According to the researchers, of all 202 donors, half passed away before age 66 and half passed away after age 66. Overall, the researchers found that the severity of the disease was closely linked to the age of the donor, with those who were older showing "the clearest and most extensive signs of CTE," "Science Now" reports. However, McKee noted that the brains many of the players whose families had reported the most concerning symptoms—such as explosiveness and self-harm—had mild levels of the CTE's distinctive abnormalities.


    Given the nature of the sample, the researchers caution that the findings can't be used to predict the prevalence of CTE among football players. "There's a tremendous selection bias," McKee said.

    Nonetheless, Jesse Mez—lead author on the paper, and a professor of neurology at Boston University School of Medicine—said, "The data suggest that there is very likely a relationship between exposure to football and risk of developing the disease."

    McKee said, "We wondered whether there's another pathology we're not capturing in the data set," such lifestyle decisions or other factors that might spark or exacerbate brain damage after trauma. "We've been looking for eight years but don't think we've captured a way to measure" all the factors that contribute CTE progression, she said.

    According to McKee, evidence suggests that early head injury may be particularly harmful. "I believe everyone needs to make [his or her] own decisions, given [his or her] own personal circumstances. But I'd definitely encourage athletes to participate in sports that don't involve head contact, and if they do, to try to adopt manners of play that reduce that impact."

    NFL response

    Meanwhile, NFL spokesperson Brian McCarthy in a statement said "we appreciate the work done by McKee and her colleagues." He said that the study leaves "many unanswered questions relating to the cause, incidence and prevalence of long-term effects of head trauma," but he added that the NFL "is committed to supporting scientific research into CTE and advancing progress in the prevention and treatment of head injuries" (Maline, Reuters, 7/25; Healy, "Science Now," Los Angeles Times, 7/25; Wilson, MedPage Today, 7/25; Tanner, AP/Sacramento Bee, 7/25; Ward et al., New York Times, 7/25; Mez et al., JAMA, 7/25) .

    Caring for concussion patients

    According to the CDC, approximately 1.3 million people sustain a form of concussion each year, while many more go unreported. Recently, concussions have received a sharp increase in national exposure. Public attention is translating into active legislation mandating considerations in concussion care for students in almost forty states.

    This research brief profiles four concussion management programs to deliver best in-class tips on how progressive providers are managing concussion care.

    Download the Brief

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