New York Rangers enforcer Derek Boogaard suffered from chronic traumatic encephalopathy, a degenerative brain ailment related to Alzheimer's disease that is caused by repeated blows to the head, the New York Times reported.

The 28-year-old Boogaard, who died in May of an accidental overdose of alcohol and the painkiller oxycodone, was found to have had CTE -- which can be diagnosed only after the death of the patient, according to the third story of an extensive three-part series on Boogaard posted on the newspaper's website Monday night.

Boogaard's family donated his brain to the Center for the Study of Traumatic Encephalopathy at Boston University's School of Medicine.

Dr. Ann McKee, the director of the centre's brain bank, saw signature brown spots near the outer surface of Boogaard's brain, which are revealing signs of CTE.

Such damage in someone as young as Boogaard was surprising. Symptoms of the condition include memory loss, impulsiveness, mood swings and addiction.

Had Boogaard lived, his condition likely would have worsened into middle-age dementia.

"To see this amount? That's a 'wow' moment," McKee said of the damage to Boogaard's brain tissue. "This is all going bad."

The disease was more advanced in Boogaard than it was in famed enforcer Bob Probert, who died of heart failure in 2010 at 45. He played 16 seasons in the NHL and often struggled with alcohol and drug addiction.

Reggie Fleming, who was 73, and 59-year-old Rick Martin, were other hockey players who were found to have CTE.

Boogaard played parts of five seasons with the Minnesota Wild before signing with the Rangers as a free agent in the summer of 2010.

In 277 career NHL games, the six-foot-eight, 257-pound Saskatoon native recorded three goals, 13 assists and 589 penalty minutes.