What Is CTE?

What is CTE?

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. In CTE, a protein called tau misfolds and malfunctions, causes other proteins to misfold, and sets off a chain reaction where this malfunctioning tau slowly spreads 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.

CTE Brain

Pictured: a control brain (left) next to a brain diagnosed with CTE. Photo courtesy of Dr. Ann McKee, MD, Boston University, VA Boston Healthcare.

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 other 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. The publication caught the attention of CLF co-founder Dr. Chris Nowinski, who envisioned the world’s first athlete brain bank. Nowinski began reaching out to the families of NFL players and other athletes who had recently passed away to arrange brain donation. He and Dr. Robert Cantu soon founded the Concussion Legacy Foundation and 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 1,000 brains donated, about two-thirds of which have been found to have CTE.

Learn more about CTE from Dr. Ann McKee, director of BU CTE Center and the VA-BU-CLF Brain Bank, by watching the video below. You can support her research by clicking here.

Symptoms of CTE

Mood and behavior symptoms

Among individuals diagnosed with CTE, some report mood and behavior symptoms that can appear as early as the patient’s 20s. Common changes seen include:

  • Impulse control problems
  • Aggression
  • Mood swings
  • Depression
  • Paranoia
  • Anxiety

Cognitive symptoms

Most patients with CTE eventually experience progressive problems with thinking and memory, including:

  • Short-term memory loss
  • Confusion
  • Impaired judgment
  • Dementia

Cognitive symptoms tend to appear later in life, often 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.

Sleep symptoms

A 2020 study from the VA-BU-CLF Brain Bank suggested that problems with sleep, specifically symptoms associated with REM behavior disorder, may be related to CTE pathology. Watch the study's corresponding author describe the findings by clicking here.

Learn more about the symptoms of CTE from Dr. Robert Stern, director of clinical research at the Boston University CTE Center:

What causes CTE?

CTE Subconcussive Impacts

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. CTE is most frequently found in contact sport athletes and military veterans. CTE has been found in individuals whose primary exposure to head impacts was through tackle football (500+ cases confirmed at the VA-BU-CLF Brain Bank), the military (50+ cases), hockey (30+ cases), boxing (20+ cases, 50+ globally), rugby (10+ cases), soccer (5+ cases, 20+ 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.

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 the age of first exposure to head impacts, the number of years of exposure, and genetics. 

Stay informed with the CTE Resources Newsletter.



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 abnormal tau protein visible. They then systematically search areas of the brain for tau in the 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 it 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 while in theory CTE could begin after one brain injury, if it does, it is rare. In populations that are exposed to years of regular, repetitive brain trauma, CTE does not appear to be rare, but we do not yet know how prevalent it is because it cannot be accurately diagnosed during life. 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.

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