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 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.

There is currently no way to definitively diagnose CTE during life. But experts have developed clinical criteria for traumatic encephalopathy syndrome (TES). TES is a clinical disorder associated with CTE. CTE is suspected in people who are at high risk due to repeated head trauma over years during sports or military experiences. A diagnosis requires evidence of degeneration of brain tissue and deposits of tau and other proteins in the brain. This can only be seen after death during an autopsy.

Some researchers are actively trying to find a test for CTE that can be used while people are alive. Others continue to study the brains of deceased individuals who may have had CTE, such as U.S. football players.

The hope is to eventually use neuropsychological tests, brain imaging such as specialized MRIs, and other biomarkers to diagnose CTE.

There is no treatment for CTE. The brain disorder is progressive, which means it continues to get worse over time. More research on treatments is needed, but the current approach is to prevent head injury. It's also important to stay informed about how to detect and manage traumatic brain injury.

You'll probably start by seeing your primary care provider. Your provider may refer you to a neurologist, psychiatrist, neuropsychologist or other specialist for further evaluation.

Because appointments can be brief and there's often a lot to discuss, prepare before your appointment.

What you can do

• Be aware of any pre-appointment restrictions. At the time you make the appointment, be sure to ask if there's anything you need to do in advance. Ask if you need to fast for blood tests.
• Write down any symptoms, including any that may seem unrelated to the reason you scheduled the appointment. Your health care provider will likely want to know details about your concern for your mental function. Try to remember when you first started to suspect that something might be wrong. If you think your symptoms are getting worse, be ready to explain why. Be prepared to discuss specific examples.
• Write down key personal information, including any major stresses or recent life changes.
• Make a list of all medicines, vitamins or supplements that you're taking.
• Make a list of your other medical conditions. Include conditions you are currently being treated for, such as diabetes or heart disease. And list any conditions you've had in the past, such as strokes.
• Take a family member, friend or caregiver along, if possible. Sometimes it can be hard to recall all the information provided during an appointment. Someone who comes with you may remember something that you missed or forgot.

Preparing a list of questions can help make the most of your time with the health care provider. List your questions from most important to least important. Some basic questions to ask the doctor include:

• What is likely causing my symptoms?
• Are there other possible causes for my symptoms?
• What kinds of tests are needed?
• Is my condition likely temporary or long-lasting? How will it likely progress over time?
• What's the best course of action?
• What are the alternatives to the primary approach being suggested?
• I have other medical issues. How can they be managed together?
• Are there any clinical trials of experimental treatments I should consider?
• Are there any restrictions?
• If medicine is being prescribed, is there a potential interaction with other medicines I am taking?
• Are there any brochures or other printed material that I can take home with me? What websites do you recommend?
• Do I need to see a specialist? What will that cost, and will my insurance cover it? You may need to call your insurance provider for some of these answers.

If you've had a concussion, some basic questions to ask your doctor include:

• What is the risk of future concussions?
• When will it be safe to return to competitive sports?
• When will it be safe to resume vigorous exercise?
• Is it safe to return to school or work?
• Is it safe to drive a car or operate power equipment?

Don't hesitate to ask questions during your appointment at any time that you don't understand something.

What to expect from your doctor

Your health care provider may ask you a variety of questions.

Questions related to symptoms:

• What symptoms are you experiencing? Any trouble with word use, memory, focus, personality or directions?
• When did symptoms begin?
• Are symptoms steadily worsening, or are they sometimes better and sometimes worse?
• How severe are symptoms?
• Have you stopped doing certain activities, such as managing finances or shopping, because of trouble thinking through them?
• What, if anything, seems to improve or worsen symptoms?
• Have you noticed any changes in the way you tend to react to people or events?
• Do you have more energy than usual, less than usual or about the same?
• Have you noticed any trembling or trouble walking?

Questions related to health history:

• Have you had your hearing and vision tested recently?
• Is there a family history of dementia or other neurological disease such as Alzheimer's, ALS or Parkinson's disease?
• What medicines are you taking? Are you taking any vitamins or supplements?
• Do you drink alcohol? How much?
• What other medical conditions are you being treated for?

If you've had a concussion, your doctor may ask questions related to events surrounding the injury:

• Have you had any previous head injuries?
• Do you play contact sports?
• How did you get this injury?
• What symptoms did you experience immediately after the injury?
• Do you remember what happened right before and after the injury?
• Did you lose consciousness after the injury?
• Did you have seizures?

Questions related to physical symptoms:

• Have you experienced nausea or vomiting since the injury?
• Have you been experiencing headaches? How soon after the injury did the headaches start?
• Have you noticed any difficulty with physical coordination since the injury?
• Have you noticed any sensitivity or problems with your vision and hearing?
• Have you noticed changes in your sense of smell or taste?
• How is your appetite?
• Have you felt lethargic or easily fatigued since the injury?
• Are you having trouble sleeping or waking from sleep?
• Do you have any dizziness or vertigo?

Questions related to cognitive or emotional signs and symptoms:

• Have you had any problems with memory or concentration since the injury?
• Have you had any mood changes, including irritability, anxiety or depression?
• Have you had any thoughts about hurting yourself or others?
• Have you noticed or have others commented that your personality has changed?
• What other symptoms are you concerned about?