Cumulative Brain Damage in Athletes Can Occur Without Concussion

Todd Murphy

June 25, 2020

Even athletes who don't experience concussion but suffer repeated jolts or falls inherent in contact sports can experience subtle and cumulative brain changes, new imaging research suggests.

A group of female college rugby players who had not experienced a concussion for at least 6 months prior to or during the study and who showed no outward symptoms of brain injury or brain changes up to 2 years later were found to have undergone changes in brain structure and connectivity.

Interestingly, no such changes were observed in the brains of female athletes who participated in the noncontact sports of rowing and swimming.

Although the rugby players' brains showed some signs of recovery during off-seasons, there was a cumulative effect of brain changes over the following years.

Senior investigator Ravi S. Menon, PhD, professor of medical biophysics at Western University in London, Ontario, Canada, said the study shows how head injuries fall on a spectrum, with concussions on one end of the spectrum and subclinical injury on the other.

"But repeated lower-impact hits can...cause similar kinds of damage that we see in concussed individuals, and the more seasons you play, the more damage you accumulate," Menon told Medscape Medical News.

The findings were published online June 17 in Neurology.


The study included 70 rugby players from Western University who played on the team during at least part of a 5-year period. Most participated in the study for 1 year, and 12 were followed for 2 years or longer. Also included were 31 female college swimmers and rowers from the same university's teams.

Menon said the investigators included noncontact athletes to assess whether any brain changes might occur that were unrelated to brain impacts but were instead related to intense exercise or team competition.

The researchers also analyzed a subset of 37 rugby players and nine rowers who wore impact accelerometer sensor headbands during practice and competition to record the impact of indirect jolts to the brain.

The Sport Concussion Assessment Tool (SCAT3) was used to assess clinical symptoms and cognitive and memory performance.

The study's primary outcome measures were diffusion and resting-state functional MRI (rs-fMRI).

Twenty-six rugby players experienced an average of three significant impacts during two practices or a preseason game, but these impacts did not cause concussion. None of the nine rowers experienced any significant head impacts.

Results showed a number of differences in the structure and connectivity in the rugby players' brains in comparison with those of swimmers and rowers.

Information Highways

The investigators found changes in white matter diffusion measures and rs-fMRI network connectivity in concussion-free contact sport athletes compared to noncontact athletes.

The researchers also found changes in connectivity in the rugby players

"In particular, mean, axial and radial diffusivities were increased with decreased fractional anisotropy in multiples white matter tracts of contact athletes accompanied with default mode and visual network hyperconnectivity (P < .001)," they report.

The rs-fMRI technology, said Menon, allowed investigators to map out "the highways in the brain — how information goes from A to B — and what we see is it's the long highways that are damaged," he said.

The brain's response to those changes, Menon said, is to increase activity in networks throughout the brain.

"The brain basically has to work harder to preserve its function, and it finds ways to do so," he said.

With nonconcussive impacts, the brain is so successful in adjusting to these changes that players exhibit no cognitive or other symptoms, Menon noted.

"Any sports medicine doctor who was to examine these people would say they're doing just fine — and they are," he said.

However, what scientists don't yet know is whether people who experience these brain changes will suffer clinical consequences later in life, he added.

"When you have a highway detour sign, you can still get to your destination. But if you have enough detour signs, represented by multiple impacts or multiple concussions, then you can no longer get from A to B. That's when you have a real problem with information flow," he added.

"Silent Problem"

Further analysis showed that the rugby players experienced some brain recovery during the off-season.

However, said Menon, the damage "just keeps going in the subsequent seasons." In fact, each of the 12 players who were followed for 2 years or more showed cumulative damage. "It's very rare to find such a pronounced effect," Menon noted.

Because these individuals display no symptoms resulting from these subtle brain changes, the findings of the study will have little influence on how physicians diagnose or treat brain injuries.

"This is a silent problem in a sense," Menon said. "I think the real message is probably more for the coaches and teams and athletic programs, which may need to reconsider how they practice — whether hitting in practice should be reduced or eliminated," he said.

Menon also noted the positive health effects of participating in team sports and other types of physical activity.

"There are probably ways to reduce the risks...without reducing the joy of the game," he said.

"Huge Ramifications"

Commenting on the findings for Medscape Medical News, Robert Cantu, MD, medical director and director of clinical research at the Cantu Concussion Center, Emerson Hospital, Concord, Massachusetts, said the research broke new ground in providing an understanding of the possible cumulative effects of head trauma in athletes.

Cantu is also a clinical professor in the Department of Neurosurgery at the Boston University School of Medicine. He was not involved with the current research.

Previous research has shown similar brain effects in athletes who have suffered head trauma short of concussion, but this study showed "those changes not only stayed over the off-season, but with successive seasons they increased, suggesting there was a cumulative effect," he said.

That is "something no prior study, to my knowledge, has shown. That has huge ramifications," Cantu said.

The knowledge can inform athletic coaches in how to conduct practices with athletes to lower the chance of head injury, he added.

What remains unknown is whether the brain can fix those changes and avoid permanent deficits later in life. "Or are we seeing structural issues that can be correlated with later-life deficits?" he asked.

Cantu said he would like to see a similar study conducted in a rodent model, which would allow researchers to take a closer look at brain changes.

The study was funded by the Schulich School of Medicine and Dentistry, Western University; the Canadian Institutes for Health Research; Brain Canada; Canada First Research Excellence Fund; and the Natural Sciences and Engineering Research Council of Canada. The investigators have disclosed no relevant financial relationships.

Neurology. Published online June 17, 2020. Abstract

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