When he published the third case, he recommended that full autopsies and comprehensive neuropathological examinations of the brain be performed on every retired NFL player who dies with a history of psychiatric, emotional, or physical problems.
Cases among football players and other athletes continued to be reported, raising sufficient attention that a research institute was initiated at Boston University in conjunction with the Sports Legacy Institute. This initiative, known as the Center for the Study of Encephalopathy, was to more fully investigate the effects of repetitive concussive and subconcussive head injuries in athletes.
In a report published in the Journal of Neuropathology and Experimental Neurology in 2009, the Boston researchers described five cases in football players as well as more than 30 in boxers. They noted that gridiron players appeared to die at younger ages, around 44, than boxers, who typically died at 60. The football players also died after shorter symptom duration -- six years rather than 20.
As with the earlier patients, symptoms included severe mood disorders, memory loss, aggressiveness, and four of the five had died tragically -- two from suicide, one during a high-speed chase by police, and another of an accidental gunshot wound.
Echoing the earlier observations of Omalu, the Boston researchers explained that they found neurofibrillary and astrocytic tangles, as well as other abnormalities, in numerous areas of the players' brains, including the dorsolateral frontal and parietal and inferior occipital cortices.
"The patchy, irregular location of the cortical [neurofibrillary tangles] and astrocytic tangles suggests that the distribution is related to direct mechanical injury from blows to the side or top of the head," they wrote.
Between 1985 and 1989, Duerson's time with the Chicago team, he was involved in more than 550 tackles.
He was a team member when the Bears defeated the New England Patriots by 46 to 10 in Super Bowl XX, and was playing for the New York Giants when they triumphed over the Buffalo Bills in Super Bowl XXV.
After retirement, he served on a panel that evaluates players' disability claims, as more former players sought support for psychiatric, emotional, and physical problems they believed related to injuries on the field.
Duerson also ran successful fast-food franchises for a while, but his life gradually deteriorated -- divorcing after being charged with battery toward his wife, selling his business at auction, and losing his home to foreclosure.
In the months before his death he confided to friends that he was experiencing depression and other symptoms, and feared that he might have chronic traumatic encephalopathy.
This possibility will be investigated by the researchers at the Boston institute, where a "brain bank" has been set up, with some 100 living NFL players offering to donate their brains for research purposes when they die.
In a note he left behind, Duerson wrote, "Please, see that my brain is given to the NFL's brain bank."
Today researchers from the Boston University institute and elsewhere are evaluating possible preventive strategies, including the use of neuroprotective substances such as omega-3 fatty acids and the experimental Alzheimer's drug Posiphen.
Risk factors also are being considered.