Concussion knowledge and application of practical guidelines in sport are based on current international concussion opinion 1-3 . A recent exponential increase in the number of concussion publications in the literature has been summarized in these consensus documents. It should be noted that the science of concussion continues to evolve. Current paradigms should be critically evaluated and periodically reviewed.
What is concussion?
Concussion is a disturbance in the brain’s ability to acquire and process information. The reduced function of the brain represents damage to nerve cells (neurons). The neurons can be damaged by a direct blow to the head, which causes the brain to rotate and/or move forward and backward. Indirect impact to the body can transfer an impulsive force to the brain which damages neurons.
The effect that this has on the athlete can vary from person to person, depending on which part of the brain is affected. The impact can cause concussion signs visible to others.
Concussion should be suspected if these signs are observed: 4
- Upper limb muscle rigidity
- Upper limb spontaneous movement
- A fit / seizure soon after contacting the surface
- Balance difficulty
- Slow responses
- Vacant stare
- Holding the head
- Facial injury
- Speech slurring
Minutes to hours after the impact injury the player may complain of:
- Nausea / Vomiting
- Blurred vision
- Memory loss / difficulty
- Not feeling right
- Sensitive to bright light & loud noise
Days to weeks after the impact the player could have/feel:
- Sleep difficulty
- Persistent low grade headache
- Poor attention & concentration
- Sad or irritable or frustrated
- Tired easily
- Lethargic, low motivation
Minimum diagnostic criteria for concussion 5
- Physical signs occurring following an impact – LOC, convulsion, balance difficulty.
- Physical signs observed by others – slowness with Q’s, aggression, emotional lability, incorrect play, vacant stare, glassy eyes.
- Any concussion symptoms.
- Any neurological / balance and cognitive examination (poor planning, unable to switch mental set 6, impaired memory & learning 7;8, reduced attention & processing information 9-12, slow reaction times 13-16
Concussion cannot be diagnosed at one point in time. Symptoms can evolve over time. Perform serial assessments over time and rule out other conditions that can mimic concussion.
The severity of traumatic brain injury is measured according to the Glasgow Coma Scale at 6h after head injury. In the neurosurgical spectrum of mild traumatic brain injury (mTBI) the Glasgow Coma Scale ranges from 13-15. mTBI is characterize by a neurological deficit and structural injury seen on CT/MRI scan.
Athletes with concussion signs and symptoms have a Glasgow Coma Scale ranging from 14 – 15 and rarely is structural injury seen on CT/MRI.
Pathophysiology and Window of Vulnerability 18;19
The following changes in the brain are implicated in concussion: Δ pattern of neuron conduction 20-22; Δ glucose metabolism 23-27; Δ membrane protein expression 28-31; Δ blood flow. The net effect is an energy deficit characterized by an acidosis and reduced neuronal activity.
An indirect marker of brains energy balance is N – acetylaspartate (NAA). NAA is measured using proton magnetic resonance spectroscopy (MRS). NAA is an index of metabolic recovery after concussion in humans. 32 This can explain the why some athletes display significant cognitive problems while conventional scans lack sensitivity to detect neurotransmitters.
NAA levels were found to be decreased for up to 30 days after concussion, long after the athlete became asymptomatic. 33 It was found that non concussed athletes may also have low NAA levels presumably due to sub concussive impacts. 34 In simple terms, while there is not enough energy, the brain can’t make NAA. The glucose deficit can also cause mitochondrial dysfunction, more likely with a second impact during the window of vulnerability. 35
How common is concussion?
1.6 to 3.8 million concussions occur in sport per year in the United States. 36 Across football codes in Australia, the probability of concussion is approximately 1 in 7.
For further information on concussion visit www.sportsconcussionaustralasia.com
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