According to the Boston University CTE Center, Chronic Traumatic Encephalopathy (CTE) is a degenerative brain disease found in athletes, military veterans, and others with a history of repetitive brain trauma. Most of what we have learned about CTE has come from the research of Dr. Ann McKee, director of the VA-BU-CLF Brain Bank, who has revolutionized our understanding of CTE. In CTE, a protein called Tau forms clumps that slowly spread throughout the brain, killing brain cells. CTE has been seen in people as young as 17, but symptoms do not generally begin appearing until years after the onset of head impacts.
Early symptoms of CTE usually appear in a patient's late 20s or 30s, and affect a patient's mood and behavior. Some common changes seen include impulse control problems, aggression, depression, and paranoia.
As the disease progresses, some patients may experience problems with thinking and memory, including memory loss, confusion, impaired judgment, and eventually progressive dementia. Cognitive symptoms tend to appear later than mood and behavioral symptoms, and generally first appear in a patient’s 40s or 50s. Patients may exhibit one or both symptom clusters. In some cases, symptoms worsen with time (even if the patient suffers no additional head impacts). In other cases, symptoms may be stable for years before worsening.
Learn more about CTE from Dr. Ann McKee, director of the VA-BU-CLF Brain Bank, by watching the video below. You can support her research by clicking here.
A brief history of CTE
CTE was first described in 1928, when Dr. Harrison Martland described a group of boxers as having “punch drunk syndrome.” Over the next 75 years, several researchers reported similar findings in boxers and victims of brain trauma, but fewer than 50 cases were confirmed. In 2005, a pathologist named Bennet Omalu published the first evidence of CTE in an American football player: former Pittsburgh Steeler Mike Webster. Shortly thereafter, the Concussion Legacy Foundation partnered with Boston University and the U.S. Department of Veterans Affairs to form the VA-BU-CLF Brain Bank, led by Dr. Ann McKee. The Brain Bank has revolutionized how we understand the disease, with more than 600 brains donated, over 360 of which have been found to have CTE.
Learn more about the symptoms of CTE from Dr. Robert Stern, director of clinical research at the Boston University CTE Center:
What causes CTE?
The best available evidence tells us that CTE is caused by repetitive hits to the head sustained over a period of years. This doesn’t mean a handful of concussions: most people diagnosed with CTE suffered hundreds or thousands of head impacts over the course of many years playing contact sports or serving in the military. And it’s not just concussions: the best available evidence points towards sub-concussive impacts, or hits to the head that don’t cause full-blown concussions, as the biggest factor.
Who is most at risk for CTE?
Every person diagnosed with CTE has one thing in common: a history of repetitive hits to the head.1 CTE is most often found in contact sport athletes and military veterans, likely because these are some of the only roles in modern life that involve purposeful, repetitive hits to the head. CTE has been found in individuals whose primary exposure to head impacts was through tackle football (200+ cases confirmed at the VA-BU-CLF Brain Bank), the military (25+ cases), hockey (20+ cases), boxing (15+ cases, 50+ globally), rugby (5+ cases), soccer (5+ cases, 10+ globally), pro wrestling (5+ cases), and, in fewer than three cases each, baseball, basketball, intimate partner violence, and individuals with developmental disorders who engaged in head banging behaviors.
|CTE has been found in...||Source of head impacts|
|Boxers||Punches to the head|
|Tackle football players||Hits to the helmet|
|Soccer players||Headers and collisions|
|Ice hockey players||Fighting, checking|
|Military veterans||Blast injuries, combat|
|Victims of domestic abuse||Repeated violence|
Importantly, not everyone who has suffered repetitive hits to the head will develop CTE. There are several risk factors at play that make some people more prone to develop CTE than others, including:
Length of exposure to head impacts
Athletes with longer careers playing contact sports are at greater risk for CTE than athletes with shorter careers. A 2019 study on deceased football players led by Boston University researchers and published in the Annals of Neurology medical journal found that the risk and severity of developing CTE among football players is not correlated to number of concussions, but is instead correlated to the number of years playing tackle football.
The study analyzed 266 deceased football players, 223 of whom had CTE and 43 of whom did not. The researchers found that the risk of CTE increases by 30 percent every year of tackle football, and doubles every 2.6 additional years. (We don’t know the risk of developing CTE after one year of playing tackle football, but it’s likely very low.) This shockingly strong relationship between years of tackle and risk of CTE may be even stronger than the link between years of smoking and risk of lung cancer.
The link is so profound that a high school football player who starts tackle football at age 5, instead of age 14, has an incredible 10 times the risk of developing the brain disease CTE.
The discovery that risk of CTE is correlated with length of career – or, years of exposure to repetitive head impacts – has remained true with other contact sports and head impact exposure groups. Researchers have also found that among those diagnosed with CTE, athletes with longer careers are more likely to have more severe pathology than those with shorter careers.
There are very likely other risk factors that have yet to be discovered, including possible genetic differences that make some people more prone to develop CTE than others. More research will help scientists determine what those factors might be, and could help us understand how to prevent and treat the disease.
Age of first exposure to head impacts
Athletes who begin playing contact sports at younger ages are at greater risk for CTE. Several published studies show that exposure to head impacts before age 12 is associated with worse outcomes than starting after age 12.
How is CTE diagnosed?
Currently, CTE can only be diagnosed after death through brain tissue analysis. Doctors with a specialty in brain diseases slice brain tissue and use special chemicals to make the Tau clumps visible. They then systematically search areas of the brain for Tau clumps with a unique pattern specific to CTE. The process can take several months to complete, and the analysis is not typically performed as a part of a normal autopsy. In fact, until recently there were relatively few doctors who knew how to diagnose CTE.
In 2015, researchers from the VA-BU-CLF Brain Bank, led by Dr. Ann McKee, collaborated with the National Institutes of Health to develop diagnostic criteria for CTE, so that any neuropathologist familiar with brain diseases can accurately diagnose CTE. This important work has made it possible for more and more scientists to be on the lookout for CTE, helping accelerate progress.
I suffered a concussion. Is that going to give me CTE?
One concussion in the absence of other brain trauma has never been seen to cause CTE.
The best evidence available today suggests that CTE is not caused by any single injury, but rather it is caused by years of regular, repetitive brain trauma. There are also many individuals who suffer years of head impacts, but do not develop CTE. More research will help us understand these factors in the future.
What treatments exist for CTE?
Treating a disease that can't be officially diagnosed until after death is difficult. Luckily there are lots of things that patients worried they have CTE can do to address their symptoms and find relief. Most treatments for CTE involve identifying the symptoms that are causing patients the most difficulty, and treating those symptoms with targeted therapies.
Mood changes, including depression, irritability, and anxiety, may be treated with cognitive behavioral therapy. Working with a cognitive behavioral therapist can help patients develop strategies that help them manage the particular mood symptoms that are causing the greatest problems.
A variety of treatment options exist for headache, including craniosacral therapy, massage, acupuncture, or medications. Working with a doctor to determine the type of headache is helpful for determining the best treatment options.
Memory training exercises, including consistent note-taking strategies, can be helpful for continuing a patient's activities of daily living, despite increasing difficulty with memory.
If you think you or a loved one has CTE, read more of our recommendations on living with CTE and check out the CLF HelpLine, where we support patients and families struggling with the outcomes of brain injury.
1. A single case report claims a Stage 2 CTE case in a 45-year-old male. However, as the authors state, "lack of a trauma history comes only from the recollection of the patient's wife," so until other cases are reported with better exposure histories, we do not consider this isolated report meaningful, although we will continue to monitor the literature closely for other possible causes of CTE.