Traumatic brain injury (TBI) results from an impact to the head that disrupts normal brain function. Traumatic brain injury may affect a person’s cognitive abilities, including learning and thinking skills.
About traumatic brain injury
The leading causes of TBI that resulted in emergency department visits were falls, being struck by an object and motor vehicle crashes. Indirect forces that jolt the brain violently within the skull, such as shock waves from battlefield explosions, can also cause traumatic brain injury. In addition, traumatic brain injury can result from bullet wounds or other injuries that penetrate the skull and brain.
Doctors classify traumatic brain injury as mild, moderate or severe, depending on whether the injury causes unconsciousness, how long unconsciousness lasts and the severity of symptoms. Although most traumatic brain injuries are classified as mild because they're not life-threatening, even a mild traumatic brain injury can have serious and long-lasting effects.
Resulting from an impact to the head that disrupts normal brain function, traumatic brain injury is a threat to cognitive health in two ways:
- A traumatic brain injury's direct effects — which may be long-lasting or even permanent — can include unconsciousness, inability to recall the traumatic event, confusion, difficulty learning and remembering new information, trouble speaking coherently, unsteadiness, lack of coordination, and problems with vision or hearing.
- Certain types of traumatic brain injury may increase the risk of developing Alzheimer's or another type of dementia years after the injury takes place.
If a head injury occurs
Traumatic brain injury injures your brain even if you don’t lose consciousness and your symptoms clear up quickly. Anyone who experiences an impact to the head and develops any symptoms of traumatic brain injury should seek medical attention, even if symptoms seem mild. Call emergency services for anyone who’s unconscious for more than a minute or two, or who experiences seizures, repeated vomiting or symptoms that seem to worsen as time passes. Seek emergency care for anyone whose head was injured during ejection from a vehicle, who was struck by a vehicle while on foot or who fell from a height of more than three feet.
According to the Centers for Disease Control and Prevention (CDC), approximately 2.87 million TBI-related emergency department visits, hospitalizations and deaths occurred in 2014, the latest year for which information is available.
Causes and risk factors
Preventing traumatic brain injury
Falls are the most common cause of traumatic brain injury, and falling poses an especially serious risk for older adults. According to a CDC special report analyzing data from several federal agencies, each year 56,000 seniors are hospitalized as a result of head injuries sustained in falls and 8,000 die as a result. When a senior sustains a serious traumatic brain injury in a fall, direct effects of the injury may result in long-term cognitive changes, reduced ability to function and changes in emotional health.
An estimated 775,000 older adults are living with traumatic brain injury-related disability. Measures to reduce the risk of falls include:
Home safety and dementia
Use our online tool, Alzheimer's Navigator®, and get a personalized action list on how to prevent falls and make your home safe for someone with dementia.
- Using a walker or other assistive device to compensate for mobility problems, muscle weakness or poor balance.
- Having your vision checked regularly and using glasses or contact lenses that correct for changes.
- Working with your doctor to watch for medication side effects or interactions among drugs you’re taking.
- Avoiding household hazards, such as clutter, loose rugs or poor lighting.
Motor vehicle crashes are another common cause of traumatic brain injury. You can reduce your risk by keeping your vehicle in good repair, following the rules of the road and buckling your seat belt. You can also protect your head by wearing a helmet and other protective equipment when biking, inline skating or playing contact sports.
Dementia and traumatic brain injury
Over the past 30 years, research has linked moderate and severe traumatic brain injury to a greater risk of developing Alzheimer's disease or another dementia years after the original head injury.
- One of the key studies showing an increased risk found that older adults with a history of moderate traumatic brain injury had a 2.3 times greater risk of developing Alzheimer's than seniors with no history of head injury, and those with a history of severe traumatic brain injury had a 4.5 times greater risk. Other studies — but not all — have found a link between moderate and severe traumatic brain injury and elevated risk.
- There’s no evidence that a single mild traumatic brain injury increases dementia risk. However, emerging evidence does suggest that repeated mild traumatic brain injuries, such as those that can occur in sports like American football, boxing, hockey and soccer, may be linked to a greater risk of chronic traumatic encephalopathy (CTE), a form of dementia.
- Previous research has shown that boxers have an increased risk of CTE, which was originally called dementia pugilistica or “punch-drunk syndrome.” The risk of CTE in boxers seems most closely tied to the number of rounds boxed, not to the number of times a boxer was knocked out, suggesting that even repeated mild traumatic brain injuries that don’t cause unconsciousness may increase dementia risk. Researchers don’t yet know whether CTE is most likely to occur following a small number of severe traumatic brain injuries, a large number of mild or very mild traumatic brain injuries, or some other pattern of head trauma. The symptoms of CTE may include memory loss, confusion, impaired judgment, impulse control problems, aggression, depression, anxiety, suicidality, parkinsonism (movement symptoms similar to Parkinson's disease), and, eventually, progressive dementia. These symptoms may begin years or even decades after the last traumatic brain injury.
- A study published in the March 23, 2016, online edition of the Journal of Neurology found that a history of traumatic brain injury may accelerate the age of onset of cognitive impairment by two or more years. These results were consistent with other studies that indicate traumatic brain injury is a significant risk factor for cognitive decline in older adults and associated with an earlier age of onset in people with mild cognitive impairment and Alzheimer’s disease.
- Another study conducted by researchers at Umeå University in Sweden confirmed traumatic brain injury as a risk factor for dementia and revealed that the risk of a dementia diagnosis was highest during the first year after the injury. During this time, people who had a traumatic brain injury were four to six times as likely to get a dementia diagnosis as those without a traumatic brain injury. The study, published in PLOS Medical Journal on January 30, 2018, also concluded that a concussion or other traumatic brain injury can increase the risk of developing dementia even 30 years later.
- More research is needed to fully understand the relationship between traumatic brain injury and dementia and to understand why moderate, severe and repeated mild traumatic brain injuries are at an increased risk. Current research on how traumatic brain injury changes brain chemistry indicates a relationship between traumatic brain injury and hallmark protein abnormalities linked to Alzheimer’s. Within hours after injury, severe traumatic brain injury has been shown to increase levels of beta-amyloid, one hallmark Alzheimer’s protein. And CTE, the dementia linked to repeated mild traumatic brain injury, appears to be most strongly characterized by deposits of tau protein, another Alzheimer’s hallmark. Beta-amyloid deposits are also found in some individuals with CTE.
- Some research suggests that traumatic brain injury may be more likely to cause dementia in individuals who have a variation of the gene for apolipoprotein E (APOE) called APOE-e4. More research is needed to understand the strength of the link between APOE-e4 and dementia risk in those who’ve had a traumatic brain injury.
Does every hit to the head lead to dementia?
Not everyone who experiences a head injury develops dementia. There’s no evidence that a single mild traumatic brain injury increases dementia risk. Although there’s no known strategy to reduce the possible long-term risk of dementia once you’ve experienced a moderate or severe traumatic brain injury, or repeated mild traumatic brain injuries, it’s important to understand that not everyone who experiences a head injury in one of these categories develops dementia. More research is needed to confirm the possible link between brain injury and dementia and to understand why moderate, severe and repeated mild traumatic brain injuries may increase risk.
The severity of symptoms depends on whether the injury is mild, moderate or severe.
Mild traumatic brain injury, also known as a concussion, either doesn’t cause unconsciousness or unconsciousness lasts for 30 minutes or less. Mild traumatic brain injury symptoms may include:
- Inability to remember the cause of the injury or events that occurred immediately before or up to 24 hours after it happened.
- Confusion and disorientation.
- Difficulty remembering new information.
- Blurry vision.
- Nausea and vomiting.
- Ringing in the ears.
- Trouble speaking coherently.
- Changes in emotions or sleep patterns.
These symptoms often appear at the time of the injury or soon after, but sometimes may not develop for days or weeks. Mild traumatic brain injury symptoms are usually temporary and clear up within hours, days or weeks; however, on occasion, they can last months or longer.
Moderate traumatic brain injury causes unconsciousness lasting more than 30 minutes but less than 24 hours, and severe traumatic brain injury causes unconsciousness for more than 24 hours. Symptoms of moderate and severe traumatic brain injury are similar to those of mild traumatic brain injury, but more serious and longer-lasting.
In all forms of traumatic brain injury, cognitive changes are among the most common, disabling and long-lasting symptoms that can result directly from the injury. The ability to learn and remember new information is often affected. Other commonly affected cognitive skills include the capacity to pay attention, organize thoughts, plan effective strategies for completing tasks and activities, and make sound judgments. More severe changes in thinking skills — a hallmark characteristic of dementia — may develop years after the injury took place and the person appears to have recovered from its immediate effects.
Evaluations by health care professionals typically include:
- Questions about the circumstances of the injury.
- Assessment of the person's level of consciousness and confusion.
- Neurological examination to assess memory and thinking, vision, hearing, touch, balance, reflexes, and other indicators of brain function.
Let your physician know if you are taking medications (prescription, over-the-counter or “natural remedies”), especially blood thinners such as Coumadin and aspirin, because they can increase the chance of complications. Also inform your health care professional if you drink alcohol or take illicit drugs.
Depending on the cause of the traumatic brain injury and the severity of symptoms, brain imaging with computed tomography (CT) may be needed to determine if there’s bleeding or swelling in the brain. If you experience a traumatic brain injury, it should be noted in your permanent medical record and mentioned whenever familiarizing a new doctor with your medical history.
Alzheimer’s disease and other dementias that may occur as a long-term result of traumatic brain injury are progressive disorders that worsen over time. As with all dementias, they affect quality of life, shorten life span and complicate the effort to manage other health conditions effectively.
The most serious traumatic brain injuries require specialized hospital care and can require months of inpatient rehabilitation. Most traumatic brain injuries are mild and can be managed with either a short hospital stay for observation or at-home monitoring followed by outpatient rehab, if needed.
Treatment of dementia in a person with a history of traumatic brain injuries varies depending on the type of dementia diagnosed. Strategies for treating Alzheimer's or another specific type of dementia are the same for individuals with and without a history of traumatic brain injury.
Alzheimer's disease and other dementias that may occur as a long-term result of traumatic brain injury are progressive disorders that worsen over time. As with all dementias, they affect quality of life, shorten lifespan and complicate the effort to manage other health conditions effectively. However, because CTE is a relatively new area of exploration for researchers and physicians, formal clinical guidelines for diagnosing and managing this condition do not yet exist. Several major research initiatives are under way to gain further insight into the patterns of injury and brain changes that may be implicated in CTE, and to develop new strategies for prevention, diagnosis and treatment.
Learn more: Treatment for Dementia, Treatment for Alzheimer's