Injured athletes are prohibited from returning to play before they are symptom-free during rest and exertion and their neuropsychological tests are normal again, in order to avoid a risk of cumulative effects such as decline in mental function and second-impact syndrome, which may occur on very rare occasions after a concussion that occurs before the symptoms from another concussion have resolved.
[5] Three grading systems are followed most widely: the first by neurosurgeon Robert Cantu, another by the Colorado Medical Society, and a third by the American Academy of Neurology.
[8] The guidelines developed by the Colorado Medical Society were published in 1991 in response to the death of a high school athlete due to what was thought to be second-impact syndrome.
[12] However, in 2013 the AAN published a revised set of guidelines that moved away from concussion grading, emphasizing more detailed neurological assessment prior to return to play.
[13] The guidelines emphasized that younger patients should be managed more conservatively and that risk of recurrent concussion was highest within 10 days following the initial injury.