Second Impact Syndrome (SIS) is an acute and potentially catastrophic complication of repetitive brain injury. Thankfully though, SIS is rare. It is a neurological condition in which a second concussion occurs before a first concussion has healed properly, causing rapid and severe brain swelling and often catastrophic results. Tragically the condition is often fatal, with those who do survive suffering severe disability.
SIS can result from even a very mild concussion that occurs days or weeks after the initial concussion. The brain may be left vulnerable from the first concussion and suffers abnormal metabolic activity. The first concussion may cause the brain to lose its ability to auto regulate intracranial and cerebral perfusion pressure. This may then lead to cerebral oedema (severe swelling of the brain) and possible brain herniation. All of these characteristics enhance the vulnerability of the brain and greatly increase the risk of death, even if the second injury is far less intense.
Most cases of SIS have occurred in young athletes, particularly those who participate in sports such as boxing, baseball, football, hockey, and skiing. If an athlete has suffered a concussion they should not return to their sport until the symptoms of the initial head injury are gone. SIS is also seen in elderly patients with recurrent subdural haematomata, as a result of mild to moderate head trauma. Children with non-accidental and repetitive brain injury can also develop SIS.
Due to the very small number of recorded cases of SIS, there is doubt about whether it is a valid diagnosis. However, the syndrome is recognised by physicians.
When SIS occurs, surgery does not help and there is little hope for recovery. Treatment requires immediate recognition and includes administration of osmotic agents and hyperventilation in order to lower intracranial pressure. When SIS is not fatal, the effects similar to those of severe traumatic brain injury can occur, including persistent muscle spasms, emotional instability, hallucinations, post-traumatic epilepsy, mental disability, paralysis, coma, and brain death.
Alison Johnson, senior associate in the clinical negligence cerebral palsy team at Penningtons Manches LLP, says: “Thankfully the incidence of SIS is extremely rare but nevertheless it is something to be aware of so precautions can be taken to prevent it occurring. Even the mildest head injury causing concussion should be treated very carefully. We represent brain-injured children and young people, some of whom have epilepsy and need to guard against further injury from seizures. A child suffering a drop attack seizure can collapse suddenly and fall to the floor. This is why many of our clients wear drop seizure helmets to minimise the chance of suffering a concussion and the risks that present to them.”