Sports-related concussion: Managing long-term effects
Although repeated concussive head trauma is a purported risk factor for later neurodegenerative disease, the problem is far from fully elucidated. "Some, but certainly not all, people with repeated concussion develop neurodegenerative problems later in life. But does the risk increase a little bit or a lot?" says Bradley F. Boeve, M.D., a consultant in Neurology at Mayo Clinic in Rochester, Minnesota.
At the severe end of the spectrum of possible effects is chronic traumatic encephalopathy (CTE), experienced by a minority of athletes. Other athletes might have long-term cognitive or neuropsychological problems, but the timing and mechanism of symptom onset and specific risk factors that might predispose individuals with sports-related concussion (SRC) to develop neurodegenerative disease aren't clear.
Mayo Clinic devotes considerable clinical and research expertise across multiple specialties to athletes with concussive injuries, from peewee to professional leagues. The goal is to relieve patient symptoms, uncover risk factors for long-term effects of SRC and make evidence-based recommendations for increasing the safety of sports.
"We have an integrated system of expertise, with a common will and drive to improve the care of people with concussive injuries and their ability to function later in their lives," says Rodolfo Savica, M.D., Ph.D., a consultant in Neurology at Mayo Clinic's campus in Minnesota.
Patients have comprehensive evaluations from consultants in behavioral neurology, brain rehabilitation and neuropsychology, headache neurology, and sports medicine. "Even if we find no definitive evidence of neurodegenerative disease, our role as clinicians is to treat the patient's symptoms," says Allen W. Brown, M.D., Brain Rehabilitation at Mayo Clinic's campus in Minnesota. "It's very common for us to see individuals who have had sports-related concussive injuries and are experiencing many symptoms unrelated to brain dysfunction."
Large population at risk
It's generally accepted that among people who experience symptoms from concussion, approximately 70 to 80 percent are no longer experiencing them two weeks later. "But that leaves 1 in 5 people who don't recover within seven to 10 days.
That's a huge population at risk," says David W. Dodick, M.D., a consultant in Neurology at Mayo Clinic in Phoenix/Scottsdale, Arizona. "The accepted number of sports-related concussions is on the order of 3.5 million to 4 million in the United States each year. I would say it's at least double that."
Concussion is significantly underreported because it can be asymptomatic, and recovery is tricky to pinpoint. "When we say 'recover,' we mean the athlete is no longer reporting symptoms and the neurological evaluation is normal," Dr. Dodick says. "However, residual symptoms may be quite vague — a little irritability or trouble sleeping — and may not be attributed to the concussion. Moreover, an athlete can truly have no symptoms, but the brain might actually not have recovered yet.
"Sometimes athletes are reluctant to report," Dr. Dodick adds. "One professional athlete told me, 'Concussion is a four-letter word in the locker room.' Athletes know that if they report symptoms, they will be taken out of the game, see a lot of doctors and undergo tests, and they might lose their positions on the team. Previous concussions may also affect the way they are viewed by future teams. That's true if you're a 12-year-old Pop Warner football player. It's even more true if you're a professional athlete."
To discern specific risk factors for long-term effects, Mayo Clinic researchers are conducting a longitudinal study of people with traumatic brain injury (TBI) who later developed Alzheimer's disease or related conditions. The study cohort is drawn from the Rochester Epidemiology Project, a collection of medical data covering virtually all residents of Olmsted County, Minnesota.
"We hypothesize that we will find no association between TBI and neurodegenerative disease overall," Dr. Brown says. "But we predict we are likely to find an increased risk of developing Alzheimer's disease and related conditions after TBI in subsets of the cohort with clinical features that have been suspected of increasing this risk, such as multiple injuries or injuries of increased severity. If so, we hope to determine the factors that isolate that group."
"We have many questions that need answers," Dr. Savica adds. "Is a concussion in a car accident the same as one when playing a sport? Are some sports less likely to have long-term consequences? Is some direction or vector of trauma better than others?"
Mayo Clinic's work with SRC is enhanced by the center's broad expertise in neurodegenerative disorders. Dr. Boeve notes that tau, the primary abnormal protein in CTE, is a target of emerging therapies for Alzheimer's disease and other tauopathies.
"There are tau-active drugs that are starting clinical trials. If they prove to be safe and effective for Alzheimer's or related conditions, they might be applicable to CTE," he says. "Athletes can benefit from Mayo Clinic's expertise in Alzheimer's disease and related neurodegenerative diseases, imaging, and brain injury rehabilitation."
Evidence to make sports safer
To further safeguard athletes' health, Mayo Clinic is at the forefront of efforts to promote change in contact sports. "To truly prevent concussion, you must understand the mechanisms of injury and then come up with strategies that are not only effective but pragmatic," says Michael J. Stuart, M.D., co-director of the Sports Medicine Program at the Rochester campus of Mayo Clinic and chief medical and safety officer for USA Hockey. "Evidence-based decision-making is critical. We're trying to make sports safer."
In an evidence-based action plan published in the March 2015 issue of Clinical Journal of Sport Medicine, Mayo Clinic researchers and colleagues called for the elimination of head hits and fighting from all levels of professional and amateur ice hockey and changes in body-checking policies. "Concussion prevention is multifaceted, involving behavior modification, education, enforcing existing rules and modifying rules," Dr. Stuart says.
Equipment design is necessary but not sufficient. Dr. Stuart notes that in contrast to football helmets, "hockey helmets have a very poor suspension system, often with a very loose strap that doesn't engage the chin. Therefore, the helmet moves around on the head and often comes off. We're very interested in improving the design and materials of the hockey helmet."
However, a better helmet can't prevent all concussions in ice hockey or football. "When an athlete has a blow to the body, force is transmitted through the body to the head. The combined linear and rotational acceleration and deceleration to the brain can cause concussion without a direct blow to the head," Dr. Stuart says. "In ice hockey, we are addressing that with various strategies — body control and awareness, open-ice awareness, sportsmanship and mutual respect."
"We're slowly starting to understand what's actually happening inside the brain — the cascade of molecular, chemical and electrical events that can lead to progressive damage," Dr. Dodick adds. "But this field is really in its infancy in terms of understanding the biology of concussion and how to manage it, how to identify those at risk of long-term consequences, and how to mitigate or prevent the long-term effects."
For more information
Smith AM, et al. Ice hockey summit II: Zero tolerance for head hits and fighting. Clinical Journal of Sport Medicine. 2015;25:78. (Erratum in Clinical Journal of Sport Medicine. 2015;25:379.)