Duerson shot himself in the chest on Feb. 17, leaving a note requesting that his brain be sent to the "NFL brain bank" for study.
Dr. Ann McKee, co-director of Boston University's Center for the Study of Traumatic Encephalopathy told reporters on a press call Monday that Duerson "had classic pathology of CTE and no evidence of any other disease," ESPN reported.
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The center is independent of the NFL but receives some funding from the league, and Duerson's brain was sent there for examination.
CTE is believed by some neurophysiologists to be common among athletes who experience repeated hard blows to the head, especially boxers, hockey players, and football players.
Autopsied brains of players reported to have had the condition show abnormalities similar in some respects to Alzheimer's disease, such as fibrillary deposits of tau protein, but different as well.
Duerson, 50 at the time of his death, was an All-Pro defensive back for the Chicago Bears in the 1980s and early 1990s. He was a successful businessman in retirement but, as the recent recession deepened, he ran into financial difficulties.
He also complained of depression, headaches, and cognitive impairments in the months before his death.
McKee termed Duerson's CTE as "moderately advanced."
She described abnormalities in the amygdala, hippocampus, and temporal and frontal lobes, other press reports indicated.
Officials at the center said Duerson's children and ex-wife had asked that the findings be released as soon as possible without waiting for a formal scientific publication.
The NFL issued a statement expressing hope that "these findings will contribute more to the understanding of CTE."
It also promised that one of its medical committees would review the Duerson findings and that the league would continue supporting research on CTE at Boston University and elsewhere.
The league instituted new rules last year requiring clearance from independent neurologists before players suffering concussions can return to action. It also stiffened rules against helmet-to-helmet hits, but criticism that the rules don't go far enough -- and also that they go too far -- persists.