A dose-response relationship exists between number of years playing hockey and risk and severity of chronic traumatic encephalopathy (CTE), new research suggests.
Early results from a study that examined donor brains showed that each additional year of ice hockey play increased the risk for CTE by 23%.
This information should be on the “radar” of all clinicians, co-investigator Jesse Mez, MD, associate professor of neurology, Boston University School of Medicine, Massachusetts, told Medscape Medical News.
“When they’re talking to kids and families and parents about playing contact sports, they should discuss the benefits as well as the risks so all that information can be taken into consideration,” he added.
Metz noted that clinicians should also consider the amount of hockey played when assessing patients for thinking and memory trouble later in life.
“CTE could be in the differential diagnosis,” he said.
The study findings will be presented at the American Academy of Neurology (AAN) 2022 Annual Meeting in April.
Football Data
CTE is a neurodegenerative disease associated with repetitive hits to the head. In previous research, the investigators showed that the more that athletes play American football, the more likely they are to develop CTE.
“Hockey, like football, involves repetitive head impacts as part of the game,” said Mez. “So we hypothesized that we would see a similar type of dose-response relationship in hockey.”
From two brain banks ― the Veterans Affairs-Boston University-Concussion Legacy Foundation and the Framingham Heart Study ― researchers accessed 74 consecutive brains from donors who had played ice hockey.
They collected information about hockey play during “pretty comprehensive” interviews with next of kin, Mez reported.
The study participants ranged in age from 13 to 91 years. The cause of death varied; most died with end-stage dementia and neurodegenerative disease, but some died of cardiovascular disease, and others from accidents.
For 9% of the individuals, the highest level of play was a youth league; 34% had reached the high school level, 30% reached the juniors/college level, and 26% played professionally.
In addition, 46% played another contact sport ― including 43% who played American football.
Primary outcomes included evidence of CTE from stage 0 (no CTE) to stage IV and severity of CTE, which was defined by the amount of neurofibrillary tangle (NFT) burden in 11 brain regions. For this burden, the score ranged from 0 (absent) to three (severe) in each region for a total range of 0 to 33.
Mez noted that in CTE, tau protein accumulates abnormally. “It typically begins in the cortex in the frontal lobe and then spreads to other parts of the brain, including to the medial temporal structures, and is widespread by stage IV,” he said.
Researchers estimated the association of duration of ice hockey play in years with each neuropathologic outcome and adjusted for age at death and duration of football play.
Consistent Findings
Results showed that of the 74 donors, 40 (54%) had CTE. Each additional year of hockey play corresponded to increased chances for having CTE (odds ratio, 1.23; 95% CI, 11% – 36%; P < .01).
This increase in risk is similar to that which was found with football players, Mez noted. This was somewhat surprising, as hockey involves fewer “hits” than football, he added.
“Hits are not as quintessential to the game of hockey as they are in football, where contacts occur with nearly every play,” he said. “In football, you have several hundred impacts over the course of a season.”
Researchers also found a 15% increase in odds for increasing one CTE stage (95% CI, 8% – 22%; P < .01), and a .03 standard deviation increase in cumulative NFT burden (95% CI, .01 – .05; P < .01).
Mez noted that the fact that the results were consistent across different outcomes “improves the validity” of the findings.
In a sensitivity analysis that excluded participants who also played football, estimates “were pretty similar” to those in the full analysis, said Mez.
The investigators have not yet examined the effect of level of hockey play, such as professionally or at the college level, on CTE risk. However, in football players, they found that level of play is another “valuable predictor of CTE pathology,” Mez said.
He added that he suspects level of play, position played, and years of play “are all probably contributing” to CTE risk.
Asking about years of play is useful in a clinical setting. “It’s very easy for a clinician to ask patients how many years of hockey they played,” said Mez.
Overall, the new results are important, as “millions of individuals” play contact sports, whether that is hockey, football, or European soccer, he added. “And for all sports, there seems to be this relationship between more play and risk of this disease.”
“Skewed” Population?
Commenting for Medscape Medical News, Frank Conidi, MD, director, Florida Center for Health and Sports Neurology, in Port St. Lucie, said he was surprised the investigators found a 23% per year increase in risk for CTE among hockey players.
Conidi has played hockey himself and works with the Florida Panthers of the National Hockey League. In his practice, he treats retired professional football players who have neurodegenerative disorders.
From his experience, the number of repetitive direct head impacts in football is significantly higher than in hockey. “Most of the forces seen in hockey are from hits to the body, where the force is transferred to the head,” said Conidi, who was not involved with the research.
He noted differences in the way hockey is played around the world. In European countries, for example, the ice surface is relatively large and the emphasis tends to be more on skill than hitting.
“It would have been interesting to have the study group analyze the data based on where the athlete grew up,” he said.
Conidi would also like to know when the participants played hockey. “The game is vastly different now than it was in the 1970s, ’80s, and early ’90s, when there was more fighting, less protective gear, and more hitting in general,” he noted.
As is the case for most studies of CTE in athletes, the study population is “skewed” because the participants likely had neurocognitive and other problems that led to their decision to donate their brain, said Conidi.
He also doesn’t believe the study should be the sole factor in a decision to continue or stop playing hockey. “We are still in the infancy stages of understanding the effects of high impact sports on athletes’ brains,” Conidi said.
The study received funding from the National Institute of Neurological Diseases and Stroke and the National Institute on Aging. Mez and Conidi have reported no relevant financial relationships.
American Academy of Neurology (AAN) 2021 Annual Meeting: Abstract 3026. To be presented April 24, 2022.
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