Second-impact syndrome
Second-impact syndrome (SIS) occurs when the brain swells rapidly, and catastrophically, after a person has a second concussion before symptoms from an earlier one have subsided.
[citation needed] In order to prevent SIS, guidelines have been established to prohibit athletes from returning to a game prematurely.
[10] The athlete may continue playing in the game after the second concussion, and may walk off the field without assistance, but symptoms quickly progress and the condition can rapidly worsen.
[11] Neurological collapse can occur within a short period,[12] with rapid onset of dilating pupils, loss of eye movement, unconsciousness, and respiratory failure.
[11] Failure of the brain stem frequently occurs between two and five minutes after the second impact,[1][2][11] and death can follow shortly.
[16] Adolescent and young adult males who play American football or hockey, or who box or ski are the most common individuals with the condition.
[26] Pathophysiological changes in SIS can include a loss of autoregulation of the brain's blood vessels,[12][27][28] which causes them to become congested.
[25] Experts advise that athletes who have had one concussion and still complain of concussion-related symptoms be prohibited from returning to the game due to the possibility of developing SIS.
[12] The American Academy of Neurology recommends that young athletes be prohibited from returning to play for at least a week in most cases of concussion.
[23] Treatment requires immediate recognition and includes administration of osmotic agents and hyperventilation[23] in order to lower intracranial pressure.
[40] Adolescents who sustain a head injury that goes unrecognized could be placing themselves at a greater risk due to the effects of longer and more diffuse cerebral swelling that occurs in their body.
[41] The adolescent brain is 60 times more sensitive to components of the metabolic chain reaction that occurs after trauma, resulting in more diffuse cerebral swelling.
[17] The prevalence of unreported trauma is common as a study showed that 25% of athletes thought that a concussion requires loss of consciousness.
[44] In part due to the poor documentation of the initial injury and continuing symptoms in recorded cases,[23] some professionals think that the condition is over-diagnosed,[1] and some doubt the validity of the diagnosis altogether.
[45] Due to the nature of the impact, the validity may be in question as subdural hematomas or other structural anomalies may directly affect the outcome.
[29] Between 1992 and 1998, reports of the condition began to be made more frequently than they had before, a fact is thought to be due to wider recognition of the syndrome by clinicians.
[1] In 1991, J.P. Kelly and others reported another football death after repeated concussions[48] and coined the term "vascular congestion syndrome".
After undergoing a head-to-head hit at football practice, a university nurse practitioner diagnosed Plevretes with a concussion and two days later was told he was allowed to resume play.
[31] The sudden collapse seen in patients may be due to a type of cerebral edema that can follow an initial impact in children and teenagers, rather than to SIS.
[45] This type of edema, referred to as diffuse cerebral swelling, may be the real reason for the collapse which young people sometimes experience and which is commonly thought to be due to SIS.
[51] Those who doubt the validity of the diagnosis cite the finding that diffuse cerebral swelling is more common in children and adolescents as an explanation for the greater frequency of SIS diagnoses in young people.
[45] They found that diagnoses of SIS were frequently based on bystander accounts of previous injuries, which they showed to be unreliable.
[14] Teammates of players who are thought to have SIS may over-report the initial concussion, giving the appearance of a greater number of second impacts than actually exist.
[18] Thus critics argue that the small number of reported cases leaves the question of whether SIS really causes the brain to swell catastrophically unanswered.
[9] Whether a second impact is really involved in the diffuse cerebral swelling that occurs on rare occasions after a mild traumatic brain injury is controversial, but some experts[who?]
