Chronic traumatic encephalopathy (CTE) is a brain disorder likely caused by repeated head injuries. It causes the death of nerve cells in the brain, known as degeneration. CTE gets worse over time. The only way to definitively diagnosis CTE is after death during an autopsy of the brain.

CTE is a rare disorder that is not yet well understood. CTE doesn't appear to be related to a single head injury. It's related to repeated head injuries, often occurring in contact sports or military combat. The development of CTE has been associated with second impact syndrome, in which a second head injury happens before previous head injury symptoms have fully resolved.

Experts are still trying to understand how repeated head injuries and other factors might contribute to the changes in the brain that result in CTE. Researchers are looking into how the number of head injuries someone experiences and how bad the injuries are may affect risk of CTE.

CTE has been found in the brains of people who played U.S. football and other contact sports, including boxing. It also may occur in military members who were exposed to explosive blasts. Symptoms of CTE are thought to include trouble with thinking and emotions, physical problems, and other behaviors. It's thought that these develop years to decades after head trauma occurs.

CTE can't be definitively diagnosed during life except in people with high-risk exposures. Researchers are currently developing diagnostic biomarkers for CTE, but none has been validated yet. When the symptoms associated with CTE occur, health care providers may diagnose traumatic encephalopathy syndrome.

Experts don't yet know how often CTE occurs in the population, but it appears to be rare. They also don't fully understand the causes. There is no cure for CTE.


There are no specific symptoms that have been clearly linked to CTE. Some of the possible symptoms can occur in many other conditions. In the people who were confirmed to have CTE at autopsy, symptoms have included cognitive, behavioral, mood and motor changes.

Cognitive impairment

  • Trouble thinking.
  • Memory loss.
  • Problems with planning, organization and carrying out tasks.

Behavioral changes

  • Impulsive behavior.
  • Aggression.

Mood disorders

  • Depression or apathy.
  • Emotional instability.
  • Substance misuse.
  • Suicidal thoughts or behavior.

Motor symptoms

  • Problems with walking and balance.
  • Parkinsonism, which causes shaking, slow movement and trouble with speech.
  • Motor neuron disease, which destroys cells that control walking, speaking, swallowing and breathing.

CTE symptoms don't develop right after a head injury. Experts believe that they develop over years or decades after repeated head trauma.

Experts also believe that CTE symptoms appear in two forms. In early life between the late 20s and early 30s, the first form of CTE may cause mental health and behavioral issues. Symptoms of this form include depression, anxiety, impulsive behavior and aggression. The second form of CTE is thought to cause symptoms later in life, around age 60. These symptoms include memory and thinking problems that are likely to progress to dementia.

The full list of signs to look for in people with CTE at autopsy is still unknown. There's also little known about how CTE progresses.

When to see a doctor

CTE is thought to develop over many years after repeated brain injuries that may be mild or severe. See your health care provider in these situations:

  • Suicidal thoughts. Research shows that people with CTE may be at increased risk of suicide. If you have thoughts of hurting yourself, call 911 or your local emergency number. Or contact a suicide hotline. In the U.S., call or text 988 to reach the 988 Suicide & Crisis Lifeline or use the Lifeline Chat.
  • Head injury. See your health care provider if you've had a head injury, even if you didn't need emergency care. If your child has received a head injury that concerns you, call your child's health care provider right away. Depending on the symptoms, your or your child's provider may recommend seeking immediate medical care.
  • Memory problems. See your health care provider if you have concerns about your memory. Also see your provider if you experience other thinking or behavior problems.
  • Personality or mood changes. See your health care provider if you experience depression, anxiety, aggression or impulsive behavior.


Repeated head trauma is likely the cause of CTE. Football players in the United States, ice hockey players and military members serving in war zones have been the focus of most CTE studies. However, other sports and factors such as physical abuse also can lead to repeated head injuries.

A head injury can cause a concussion, which may cause headaches, problems with memory and other symptoms. Not everyone who experiences repeated concussions, including athletes and military members, go on to develop CTE. Some studies have shown no increased incidence of CTE in people exposed to repeated head injuries.

In brains with CTE, researchers have found that there is a buildup of a protein called tau around the blood vessels. Tau buildup in CTE is different from accumulations of tau found in Alzheimer's disease and other forms of dementia. CTE is thought to cause areas of the brain to waste away, known as atrophy. This happens because injuries to nerve cells that conduct electrical impulses affect communication between cells.

It's possible that people with CTE may show signs of another neurodegenerative disease, including Alzheimer's disease, amyotrophic lateral sclerosis (ALS), Parkinson's disease or frontotemporal lobar degeneration, also known as frontotemporal dementia.

Risk factors

Repeated exposure to traumatic brain injury is thought to increase the risk of CTE. Experts are still learning about the risk factors.


There is no treatment for CTE. But CTE may be prevented because it's associated with recurrent concussions. People who have had one concussion are more likely to have another head injury. The current recommendation to prevent CTE is to reduce mild traumatic brain injuries and to prevent additional injury after a concussion.

Chronic traumatic encephalopathy care at Mayo Clinic

Nov. 18, 2023
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