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Largest CTE study to date finds evidence of disease in 6% of all test subjects, over 28% in former boxers

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The study of 750 people broke down the frequency of CTE across sports.

Dr. Ann C. McKee...
File photo - Dr. Ann C. McKee, Director of Boston University’s CTE Center and Chief of Neuropathology at the VA Boston Healthcare System, does an autopsy on the brain of an NFL player who died in his 40s and donated his brain to to the VA-BU-CLF Brain Bank in the Jamaica Plain neighborhood of Boston, July 12, 2017.
Photo by Stan Grossfeld/The Boston Globe via Getty Images

Medical Xpress reports that a team from the University of Texas Health Science Center, lead by Dr. Kevin Bieniek, has recently released their findings after conducting the ‘largest ever’ study on chronic traumatic encephalopathy (CTE).

The research article detailing the study, titled ‘Association between contact sports participation and chronic traumatic encephalopathy: a retrospective cohort study’, was first published by the international journal Brain Pathology in June.

Bieniek’s research involved studying brain samples from 300 former athletes and 450 non-athletes to determine the prevalence of CTE — a condition that is caused most often by repeated blows to the head (both concussive and sub-concussive) — in a large pool of people that was representative of the general population of the U.S.

The scientists discovered evidence of CTE in 42 brains, which accounts for 5.6% of the total brains examined. Of those 42 brains, 27 of them belonged to athletes. All but one of the 42 brains which tested positive for CTE belonged to men. The scientists determined whether a subject was an athlete by studying obituaries and high school year books.

“The 42 cases, or 6%, is more of a grounded, realistic number,” said Bieniek. “That might not seem like a lot, but when you consider there are millions of youth, high school and collegiate athletes in the United States alone who play organized sports, it has the potential of being a significant public health issue. There are many ongoing questions regarding CTE pathology, however, and we don’t want to discourage sources of healthy physical and cardiovascular activity like these sports. Rather, we emphasize safe strategies to reduce the possibility of head injuries and properly treat them when they are sustained.”

Bieniek advised some caution when evaluating the 15 cases of CTE in ‘non-athletes’. He stated that it was possible that those individuals did engage in contact sports despite their biographical information not mentioning it. Bieniek also warned that there are other diseases that, during an autopsy, appear very similar to CTE. Alzheimer’s disease, for example, features the near identical clumping of tau proteins that has been discovered in the brains of CTE sufferers.

Though this study featured the largest pool of samples ever screened for CTE, hundreds of former athlete brains have already been sporadically tested for the disease. Over the past few years, it is believed that 80-99% of all autopsied brains of professional football players show evidence of CTE.

In Bieniek’s study 15% of the test subjects that played American football tested positive for CTE. The study showed that participation in American football beyond high school resulted in a much higher risk of developing CTE.

Bieniek told Bloody Elbow that his team were only able to identify seven subjects within their pool who they could classify as combat sports athletes. Four of those individuals boxed in high school, two were amateur boxers, and one boxed professionally.

Of those seven subjects, two subjects were CTE-positive (the pro boxer and one of the amateurs). That frequency translates to over 28% of combat sport athletes within the study’s testing pool testing positive for CTE. That is almost double the frequency of individuals who played American football. However, the sample size for combat sports athletes in the study is far smaller than American football players.

In 2015 Bieniek conducted a different study on CTE where he analyzed the brains of eight boxers. Two of those brains tested positive for CTE. That is a frequency of 25%.

The Concussion Foundation states that there are over 65 cases of boxers testing positive for CTE. CTE has been discovered in the brains of two former MMA fighters; Jordan Parsons (who was killed by a drunk driver in 2016) and Tim Hague (who died from a traumatic brain injury he sustained in a boxing match in 2017).

In the most recent study by Bieniek his team discovered the following frequencies of CTE for athletes in other sports:

  • Baseball - 7.8% (64 subjects)
  • Basketball - 5% (92 subjects)
  • Hockey - 5% (20 subjects)
  • Wrestling - 2.6% (39 subjects)
  • Soccer - 0% (5 subjects)

In the conclusion of that study Bieniek and his team described why it is important to learn about the frequency of CTE in both athletes and non-athletes.

“Understanding the frequency of chronic traumatic encephalopathy pathology in a large autopsy cohort with diverse exposure backgrounds provides a baseline for future prospective studies assessing the epidemiology and public health impact of chronic traumatic encephalopathy and sports related repetitive head trauma.”

When speaking with Medical Xpress Bieniek stated how ‘crucial’ brain donors were for the study of CTE, which is currently incurable.

“We are so grateful for the many patients and normal older persons who have signed on to be brain donors after their death. The program runs 24/7/365, is free to the family, and gives the family the peace and knowledge of a definitive diagnosis for their loved one’s condition.”

Symptoms of CTE include cognitive impairment, impulsivity, memory loss, depression, emotional instability, increased chance of substance abuse, and suicidal thoughts and behaviour. The Mayo Clinic advises that any individual who is experiencing these symptoms, and who has a history of blows to the head, should contact their doctor as soon as possible.