Dr. Ann McKee, director of neuropathology at the Bedford VA Medical Center and co-director of Boston University's Center for the Study of Traumatic Encephalopathy, examined Boogaard's brain and determined it showed signs of early CTE -- a post-mortem diagnosis he shared with more than 50 other athletes, including other hockey players, football players, wrestlers and boxers, according to the center's research.
"Unfortunately this finding does not contribute to our knowledge of the risks of normal hockey play for most participants, as very few hockey players engage in as many fights as Boogaard," Chris Nowinski, who co-directs the Center for the Study of Traumatic Encephalopathy with McKee, said in a statement. "Athletes and parents should know that anyone who experiences repetitive brain trauma may be at risk to develop CTE, but we are hopeful that risk is small in hockey."
Boogaard was one of the NHL's most aggressive players, reportedly participating in more than 60 regular season fights. According to his family, Boogaard had his "bell rung" at least 20 times, but reported few concussions to his team or medical staff.
CTE shares features with Alzheimer's, Parkinson's and Lou Gehrig's disease. When severe, it can lead to dementia, impulsivity and rage.
In the two years before his death, Boogaard suffered from emotional instability, impulse control problems, short-term memory loss and disorientation. His death came months before the apparent suicides of two fellow NHL 'enforcers', 35-year-old Wade Belak of the Nashville Predators and 27-year-old Rick Rypien of the Winnipeg Jets.
"… based on the small sample of enforcers we have studied, it is possible that frequently engaging in fistfights as a hockey player may put one at increased risk for this degenerative brain disease," Center for the Study of Traumatic Encephalopathy co-director Dr. Robert Cantu said in a statement.
Boogaard's brain is one of 99 athlete brains already received by the VA Brain Bank. Of 70 analyzed, more than 50 have shown signs of CTE.
"In the last three-and-a-half years, we have made dramatic, really remarkable gains in understanding the nature of this disease: how it progresses through the nervous system; what kind of symptom to expect at each stage," McKee told ABC News in October. "The hope is that now that we know what it is we're dealing with, we can really address with research and basic science how to prevent it, how to slow it down or how to cure it."
More than 500 living athletes, including more than a dozen former hockey players, have agreed to donate their brains to the VA Brain Bank -- a gift they hope will protect future athletes.
"I think this is an enormous problem for athletes," McKee said of CTE. "By signing on to this research, they promote their own long-term safety and certainly the safety of future players."