title: What Definition Is Used to Describe Second Impact Syndrome in Sports? A Systematic and Critical Review.
abstract: Concern about what has been termed, "second impact syndrome" (SIS) is a major factor determining return-to-play decisions after concussion. However, definitions of SIS vary. We used Scopus to conduct a systematic review and categorize the definitions used to describe SIS. Of the 91 sources identified, 79 (87%) clearly specified that SIS involved either cerebral edema or death after a concussion when a prior concussion had not resolved. Twelve articles (13%) could be interpreted as merely the events of two consecutive concussions. Among the articles that listed mortality rates, nearly all (33/35, 94%) said the rate of death was "high" (e.g., 50% to 100%). Our review found that most articles define SIS as a syndrome requiring catastrophic brain injury after consecutive concussive episodes. Given that it is unclear how common it is to have a second concussion while not fully recovered from a first concussion, the actual mortality rate of SIS is unknown.
authors.affiliation: 1Department of Family Medicine and Community Health, University of Minnesota, Minneapolis, MN; 2University of Minnesota Medical School, Minneapolis, MN; 3Bio-Medical Library, University of Minnesota, Minneapolis, MN; 4Section of Sports Medicine, Faculty of Health Sciences, University of Pretoria, Pretoria, South Africa; and 5Department of Emergency Medicine, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa.
authors.forename: Steven D
authors.initials: SD
authors.lastname: Stovitz
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Weseman
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Hooks
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Schmidt
authors.forename: Jonathan B
authors.initials: JB
authors.lastname: Koffel
authors.forename: Jon S
authors.initials: JS
authors.lastname: Patricios
mesh_terms: D001265:Athletic Injuries / Q000145:classification* / Q000175:diagnosis*; D038622:Internationality; D038223:Post-Concussion Syndrome / Q000145:classification* / Q000175:diagnosis*; D017410:Practice Guidelines as Topic; D012660:Semantics; D063189:Symptom Assessment / Q000145:classification / Q000592:standards; D013577:Syndrome; D009626:Terminology as Topic