Though the incidence of<unk>  is unknown, the condition is rare; very few cases have been confirmed in medical literature. The controversy surrounding the existence of<unk>  may play a role in the known and recorded incidence. The United States seemingly has far more reported cases of<unk>  than elsewhere. The patients affected most often include young adults and adolescents that are 16 to 19 years old. Adolescents that 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. 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. After the initial concussion, the children and young adults are more likely to sustain a<unk><unk>  within the first two weeks. In athletics, the susceptible population includes those that participate in contact sports such as American football, boxing and hockey. In the 13-year period from 1980–1993, 35 American football related cases of SIS were recorded, but only 17 of these were confirmed by autopsy or surgery and magnetic resonance imaging to be due to SIS, and 18 cases were found to be probably SIS-related. Additionally, the initial trauma commonly goes unreported, adding to the confusion about how often the syndrome occurs. The prevalence of unreported trauma is common as a study showed that 25% of athletes thoughts that a concussion requires loss of consciousness. It is found in a study by Sullivan et al that 83% of male rugby athletes were aware of concussion signs and symptoms but only 50% understood or were aware of the protocol to return to play after an injury. When coaches were surveyed, it is found that 45% of participants did not believe immediate removal from play is warranted after a concussion. Of this group surveyed, 62% was the amount that identified proper post concussion management and this lack of proper post concussion management could lead to SIS. Both direct blows to the head and blows to the body can produce the subdural hematomas, diffuse cerebral edema, subarachnoid hemorrhage and ischemic stroke, all pathologies that can lead to death. By one estimate, the syndrome kills four to six people under the age of 18 per year. According to the Centers for Disease Control, about 1.5 people die each year from a concussion in the US; in most of these cases, the person had received another concussion previously. In the presence of<unk> , the mortality rate is at best 50% when diffuse cerebral swelling occurs. In part due to the poor documentation of the initial injury and continuing symptoms in recorded cases, some professionals think that the condition is over-diagnosed, and some doubt the validity of the diagnosis altogether. Due to the nature of the<unk> , the validity may be in question as subdural hematomas or other structural anomalies may directly affect the outcome. Along with the short term effects that occur with<unk> , improper care for concussions can lead to longer term effects as well. These include early onset dementia or Alzheimer's, and early onset of Parkinson's disease. Along with an increase of loss of vision and risk of stroke can occur further on in their lives.
Second-impact syndrome
Post-intensive care syndrome
Sandifer syndrome
Tumor lysis syndrome
Overlap syndrome
Majeed syndrome
Compartment syndrome
Edwards syndrome