What is second injury syndrome (SIS) in postconcussive syndrome (PCS)?

Updated: Jul 25, 2019
  • Author: Roy H Lubit, MD, PhD; Chief Editor: David Bienenfeld, MD  more...
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Answer

Second injury syndrome (SIS), although rare, is important as a cause of preventable sudden death. SIS occurs when someone not yet fully recovered from a head injury experiences a second head trauma. After a brief delay, the person suddenly loses consciousness. Signs of brainstem compression follow, leading to death or permanent coma. The syndrome typically affects young men who participate in contact sports who do not adequately rest after a concussion before participating in the sport.. The mechanism may be failed cerebral autoregulation with subsequent engorgement of the brain vasculature.


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