Chronic Traumatic Encephalopathy (CTE)

What CTE is

CTE is a type of neurodegeneration. Repeated head impacts appear to trigger the abnormal buildup of tau, a protein that normally supports brain cells, in a distinctive pattern around small blood vessels in the folds (sulci) of the brain's surface. Over time, tau spreads, brain cells die, and the brain shrinks.

CTE was first described in boxers in the 1920s as "punch-drunk syndrome". Interest grew after it was found in the brains of former professional football players, and it has since been identified in soccer, ice hockey, rugby, wrestling and military veterans.

Risk factors

• Number and duration of head impacts: the strongest factor is total years of exposure to repetitive impacts, not just the number of recognized concussions
• Age of first exposure: some studies suggest starting tackle football at a young age increases risk
• Position and sport: linemen in American football, who receive frequent hits, and boxers
• Military blast exposure
• Possibly genetic factors

Most people who have had a single concussion, or a few, do not develop CTE.

Symptoms

Symptoms usually appear years or decades after the head impacts, commonly in a person's 40s or 50s, although younger cases occur.

Thinking and memory

• short-term memory loss
• difficulty planning, organizing and multitasking (executive function)
• poor concentration and judgment
• progressing in some to dementia

Mood and behavior

• depression and hopelessness
• irritability, short temper and aggression
• impulsivity, including substance misuse and gambling
• anxiety, paranoia and apathy
• suicidal thoughts

Movement (later stages)

• slowed movements, stiffness and tremor resembling Parkinson's disease
• speech difficulties
• balance and walking problems

Researchers have described two broad patterns: one beginning in younger adults with mood and behavior problems, and another beginning later with memory and thinking decline.

Stages

Pathologists grade CTE from stage I to IV based on how widespread tau is in the brain at autopsy. Early stages involve small patches, often in the frontal lobes. Later stages involve wide areas including memory centers, with marked brain shrinkage. These stages broadly match increasing symptom severity, though not perfectly.

Diagnosis

• Definitive diagnosis: only possible by examining brain tissue after death
• Traumatic encephalopathy syndrome (TES): in 2021, an NINDS consensus panel published research criteria for diagnosing a clinical syndrome in living people, based on substantial exposure to repetitive head impacts, core symptoms of cognitive impairment or neurobehavioral dysregulation, and a progressive course. TES indicates CTE is possible, probable or suggestive, but cannot confirm it

Doctors will also look for other, sometimes treatable, causes of similar symptoms:

• neuropsychological testing
• MRI to look for other brain injuries, strokes or tumors
• blood tests such as thyroid function and vitamin B12
• screening for depression, sleep disorders, sleep apnea and substance use

Tau PET scans and blood biomarkers are being studied but are not yet used for routine diagnosis.

CTE vs other conditions

Treatment and support

There is no cure or proven treatment to slow CTE. Care focuses on symptoms and quality of life:

• Depression and anxiety: psychotherapy and antidepressants
• Memory and thinking: cognitive rehabilitation, routines, reminders, and sometimes medicines used for dementia
• Sleep: treating insomnia and sleep apnea
• Substance use: addiction support
• Movement symptoms: physical therapy, and sometimes Parkinson's medicines
• Healthy habits: exercise, social engagement, blood pressure control, limiting alcohol
• Family and caregiver support, and planning for the future

Prevention

• reduce head impacts in practice and games, for example by limiting full-contact practices
• delay tackle football and heading in soccer for young children, as many sports bodies now recommend
• teach safe tackling and enforce rules against hits to the head
• remove athletes from play after a suspected concussion and allow full recovery before return
• use protective equipment, though helmets protect against skull fractures more than concussion

Frequently asked questions

What are the symptoms of CTE?

Common symptoms are memory and thinking problems, depression, irritability, impulsivity, aggression and suicidal thoughts. In later stages, people may develop dementia, slowed movements, tremor and speech problems. Symptoms often appear years after head impacts have stopped.

Can CTE be diagnosed in living people?

Not definitively. CTE can be confirmed only by examining the brain after death. Doctors can diagnose traumatic encephalopathy syndrome in living people based on head impact exposure and symptoms, which suggests CTE is possible or probable.

How many concussions cause CTE?

There is no set number. CTE is linked more strongly to years of repeated head impacts, including many hits that do not cause concussion symptoms, than to the number of diagnosed concussions. Most people with one or a few concussions do not develop CTE.

Is CTE the same as Alzheimer's disease?

No. Both involve tau protein, but CTE has a distinct pattern of tau around blood vessels in the brain's folds and is associated with repeated head impacts. Alzheimer's typically starts with memory loss and also involves amyloid plaques.

Can CTE be prevented?

The only known way to reduce risk is to reduce exposure to repeated head impacts. This includes limiting contact in youth sports, safer playing rules, fewer full-contact practices, and proper management of concussions.