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What is concussion?

Concussion is a mild traumatic brain injury (TBI) that occurs as a consequence of a strong blow to the head or any part of that body in which the impulsive force is transmitted to the head. This causes the brain to move rapidly in the skull back and forth in a whiplash-like fashion, resulting in a diffuse brain injury.

Rotational forces common in concussion result in diffuse injuries meaning the injury can affect multiple areas of the brain. Diffuse injuries include:

  • Diffuse axonal injury, which is widespread damage to the white matter
  • Ischemic brain injury, which results from an insufficient blood supply to the brain and is the main cause of secondary injuries
  • Vascular injury, which causes cell death shortly after injury
  • Swelling, which can lead to a dangerous increase in intercranial pressure

This impact of the brain against the skull can result in diffuse axonal injury, which is widespread damage to the white matter of the brain. Vascular injury after head trauma

The term concussion, whilst useful, can lead to confusion as many believe you must lose consciousness, despite the fact this is not the case in many concussions. Further, the term is defined differently by different author groups. The terms mild TBI and concussion are often used interchangeably, however, there is ongoing discussion as to whether concussion is actually part of the TBI spectrum. Furthermore, there are concerns that such operational definitions do not give insight into the underlying processes through which the brain is impaired by concussion.

An expert panel at a concussion panel in Berlin in 2016 defined concussion as follows:

Concussion is a traumatic brain injury induced by biomechanical forces. Several common features, such as whether it was caused by a direct jolt to the head or elsewhere on the body, may be utilized in clinically defining the nature of a concussive head injury.


What are the signs and symptoms of a concussion?

Signs of concussion usually appear a few minutes or hours after a head injury; however, occasionally it may take a few days for an individual to show symptoms. Following a concussion an individual may present the following symptoms:

  • Feeling of pressure in the head
  • Temporary loss of consciousness
  • Confusion
  • Dizziness
  • Nausea and vomiting
  • Slurred speech
  • Fatigue

Concussions are common in athletes who play contact sports such as boxing and American football, those who are suspected to have a concussion, due to showing signs listed above, are evaluated by a healthcare professional who provides return-to-play clearance once symptoms are no longer present.

Head trauma is also very common among young children, signs of concussion in infants and toddlers can include:  

  • Crying excessively
  • Change in eating or sleeping patterns
  • Lack of interest in favorite toys


How is concussion diagnosed?      

When diagnosing a concussion, clinicians or other healthcare professionals will observe for signs and symptoms, as well as ask the patient questions about their injury. Furthermore, they may perform neurological examinations, cognitive testing and use brain imagine methods.

Neurological examination assesses a patients brain function by checking vision, eye movements, hearing, strength of sensation, reflexes and balance.

During cognitive testing clinicians examine cognitive skills during a neurological exam to evaluate factors such as memory, concentration and ability to recall information.

Brain imaging testing may be recommended for individuals with severe symptoms or symptoms that are becoming worse to determine whether this is a result of brain swelling or bleeding. A CT scan is the standard test used to assess an injury to the brain, as it is able to produces cross-sectional images of the brain using a series of X-rays.

Alternatively, to diagnose complications that may occur following concussion, MRI scans can be utilized to identify changes in the brain using powerful magnets and radio waves that produce detailed images.


What is post-concussion syndrome?

Post-concussion syndrome is a disorder in which concussion symptoms last for weeks and sometimes months after the initial trauma. For most patients, symptoms occur within 7–10 days of injury and persist for up to 3 months, these symptoms include:

  • Irritability and other personality changes
  • Concentration and memory complaints  
  • Anxiety
  • Insomnia
  • Blurry vision

The risk of post-concussion syndrome is not associated with the severity of the initial injury and experts believe it is caused by structural damage such as injury to axons due them stretching.


What is chronic traumatic encephalopathy?

Chronic traumatic encephalopathy (CTE) is a progressive degenerative disorder that can cause symptoms similar to Alzheimer’s disease and is believed to be associated with a history of repeated head impacts, such as concussions and sub-concussive head impacts sustained during sport. CTE has previously been referred to as ‘punch drunk syndrome’ as it has been diagnosed during the post-mortem of some boxers.

Repeated head trauma can prompt progressive degeneration of brain tissue, including the build-up of abnormal tau protein tangles. These physical changes can occur months, years or even decades after the last head injury and lead to symptoms of CTE such as memory loss, impaired judgement and progressive dementia.

Research has suggested that individuals who have experienced repetitive head impacts in early or midlife have an increased risk of dementia later in life. However, the exact relationship between the two is not clear, especially since mild head impacts are not well recorded.

Furthermore, research surrounding CTE is limited as it can only be diagnosed after death. Therefore, researchers are working on ways to diagnose CTE in living people, which will result in accelerating this field of research.

Currently, there is no evidence that a single concussion increases the risk of neurodegenerative disease, and not everyone with a history of repetitive head impacts will go on to develop CTE or other neurodegenerative diseases.

Recognition that CTE is common in retired athletes from sports such as boxing and football has led to increased interest in this condition. Therefore, leading to more research investigating whether being exposed to repeated head impact can increase risk of developing neurodegenerative diseases.