Former NHL tough guy Bob Probert, who died last summer at the age of 45, had the degenerative brain disease known as CTE, researchers announced Thursday.

Doctors at the Center for the Study of Traumatic Encephalopathy at Boston University School of Medicine say Probert had early but definite signs of chronic traumatic encephalopathy.

The details of Probert's brain analysis will be published in an academic medical journal, but the Probert family wanted the diagnosis made public today, to help raise awareness of the dangers of brain trauma in sports.

Probert died last July of a heart attack. CTE didn't play a role in his death.

CTE is a degenerative condition caused by repeated concussions and hits to the head. It can cause permanent behavioural changes, as well as memory problems and full-out dementia. It's also been called "punch-drunk syndrome," a term once used to describe the behavioural changes seen in many boxers later in life.

Probert becomes only the second hockey player studied by Boston researchers to have been diagnosed with the degenerative disease.

Reggie Fleming, a 1960s NHL tough guy who played before helmets became mandatory, was also diagnosed with CTE after his July, 2009, death. (CTE can only be confirmed through autopsy.) He was 73 and had suffered for years from dementia.

Probert was a hockey scrapper who was involved in more than 200 fights during 16 seasons with the Detroit Red Wings and Chicago Blackhawks. His 3,300 penalty minutes ranks fifth on the NHL's career list.

Off the ice, Probert also struggled with alcohol and cocaine abuse, and was arrested a number of times for bar fights and assaults on police officers.

Probert suffered at least three diagnosed concussions, and in his 40s, he began to show some of the signs of CTE, such as odd bouts of rage and problems with his short-term memory.

In his final years, Probert agreed to donate his brain to the CSTE at Boston University. The group has been at the forefront of research into head trauma in sports, and has received a US$1 million gift from the NFL, which it has pushed for better treatment of concussions.

Dr. Robert Cantu, the co-director of the CSTE, told the New York Times that he and his fellow researchers might never know whether the game of hockey itself caused Probert's CTE, or whether it was the fighting.

"We haven't definitely established that the skills of hockey as a sport lead to a certain percentage of participants developing CTE. But it can happen to hockey players, and while they're still relatively young," he told the newspaper.

Donald Fehr, the executive director of the NHL players union, said the findings on Probert should not be taken lightly.

"Obviously, when you have a finding like this, it raises concerns and it bears serious examination," Fehr told the newspaper.

The revelation about Probert comes as the NHL and hockey in general grapples with growing evidence that concussions and other head injuries sustained in the game can have life-long consequences.

With the sidelining of star player Sidney Crosby with concussion symptoms, a debate has erupted of late about the need for rule changes at all levels of hockey and better concussion protection and protocols for returning players to the game after hard hits.

CSTE researchers have studied the brains of 40 athletes, including former football and hockey players, as well as professional wrestlers and boxers. So far, more than 30 have shown signs of CTE.

Most recently, the brain bank received the brain of former NFL player Dave Duerson, who committed suicide two weeks ago.

The centre was created in 2008 as a collaboration between Boston University and the Sports Legacy Institute. SLI co-founder and CEO Chris Nowinski says the long-term effects of repeated head trauma is starting to become clear.

"We are only beginning to appreciate the consequences of brain trauma in sports," Nowinski said in a statement Thursday.

"Early evidence indicates that the historical decision not to discourage contact to the head was an enormous mistake, and we hope aggressive changes continue to be made to protect athletes, especially at the youth level."

With files from the Associated Press