A lifetime of hockey fighting may have contributed to the death of NHLer Derek Boogaard, but it's important not to over-interpret tests that show the enforcer had the neurodegenerative disease CTE.

Doctors with Boston University's Center for the Study of Traumatic Encephalopathy announced Tuesday that an examination of Boogaard's brain showed that he had early-stage CTE damage in his cerebral cortex.

CTE, or chronic traumatic encephalopathy, is a disease that slowly degenerates the brain, much like Alzheimer's disease. The condition, once called "punch drunk syndrome" is thought to be caused by repeated concussions.

Dr. Robert Cantu, co-director of CSTE, says it's possible that Boogaard's role as a fighter may have led to the CTE.

"Boogaard's clinical history was complex, so it is unclear as to if or how much CTE contributed to his behavior, addiction or death," he said in a statement announcing the findings.

"However, based on the small sample of enforcers we have studied, it is possible that frequently engaging in fist fights as a hockey player may put one at increased risk for this degenerative brain disease."

Fellow CSTE co-director Dr. Chris Nowinski says the risks of hockey fighting may not affect most recreational hockey players.

"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," Nowinski said.

"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," he added.

The Boston team noted that although Boogaard had a mild form of CTE, his brain changes were more severe and advanced than most other athletes of similar age with CTE.

Boogaard had been diagnosed with post-concussion syndrome twice before his death. His family says he spoke of having his "bell rung" -- a term often used to describe a mild concussion -- at least 20 times.

Over time, CTE can cause dementia-like symptoms, such as memory loss, personality changes, impulsiveness, and addiction. There is no known cure or treatment for the condition. It can only be diagnosed after death, by examining slices of the brain.

Boogaard was just 28 when he was found dead in his Minneapolis apartment last May. An autopsy revealed he had died from an accidental overdose of drugs and alcohol.

Neuropathologist and CSTE co-director Dr. Ann McKee told the Times that the kind of brain damage she saw in Boogaard's brain was surprising in one so young as he. She said Boogaard's CTE was more advanced than it was in famed enforcer Bob Probert, who died of heart failure in 2010 at 45 and also struggled with addiction.

McKee also told the paper that had Boogaard lived until middle age, his condition likely would have worsened into full dementia.

Before his death, Boogaard had become withdrawn and was experiencing memory problems. He had also been heavily abusing narcotic pain relievers for close to two years.

The Boston team says it's unclear if Boogaard's behaviour changes and substance abuse were caused by the impulse control problems associated with CTE.

NHL Commissioner Gary Bettman told the Times the league was not rushing to conclusions about findings that suggest a link between CTE and hockey.

"There isn't a lot of data, and the experts who we talked to, who consult with us, think that it's way premature to be drawing any conclusions at this point," Bettman said. "Because we're not sure that any, based on the data we have available, is valid."

A number of boxers and more than 20 former NFL players have also been diagnosed with CTE after their deaths.

Boogaard is now the fourth hockey player to have been found with the brain disease. Along with Probert, Reggie Fleming, who was 73, and 59-year-old Rick Martin, also had signs of the illness.

Boogaard was an impressive six-foot-eight and weighed about 260 pounds in his prime. He played parts of five seasons with the Minnesota Wild before signing with the New York Rangers as a free agent in the summer of 2010.

Boogaard, who was nicknamed "The Boogeyman," was known more for his fists than his scoring. In 277 career NHL games, he recorded only three goals, as well as 589 penalty minutes. He also fought on the ice more than 180 times since his junior days, according to hockeyfights.com.