To the Editor Rivara et al used such a highly restricted definition of evidence in their “Consensus Statement on Sports-Related Concussions in Youth Sports Using a Modified Delphi Approach,”1 they forgot to mention the well-recognized dangers of second impact syndrome (SIS). A correction should be issued.
As with those rare cases of incipient chronic traumatic encephalopathy that have been found in US high school football players,2 cases of SIS are few in the historical record and confusing especially in historical hindsight.3 But it is nevertheless a surprising error of omission to allow such highly restrictive definitions of medical evidence to conceal rare occurrences without even so much as a caveat.