When the former N.H.L. enforcer Todd Ewen died in September, reportedly of a self-inflicted gunshot, his brain was sent to researchers. Years of memory loss and undiagnosed depression led to speculation that Ewen, 49, was afflicted with chronic traumatic encephalopathy, or C.T.E., the degenerative brain disease caused by repeated blows to the head.
On Wednesday, researchers in Toronto announced that Ewen did not have C.T.E., upending presumptions about the disease and raising more questions about why some athletes get it and some do not, even those displaying some of C.T.E.’s classic symptoms.
“These results indicate that in some athletes, multiple concussions do not lead to the development of C.