NFL greats Tony Dorsett, Joe DeLamielleure and Leonard Marshall recently received the diagnosis that they have signs of CTE, the degenerative brain disease linked to depression and dementia and attributed by some scientists to head trauma. (5:15)

BEVERLY HILLS, Calif. -- Pro Football Hall of Famers Tony Dorsett and Joe DeLamielleure, and former NFL All-Pro Leonard Marshall have been diagnosed as having signs of chronic traumatic encephalopathy, a degenerative condition many scientists say is caused by head trauma and linked to depression and dementia, doctors have told "Outside the Lines."

The three former stars underwent brain scans and clinical evaluations during the past three months at UCLA, as did an unidentified ex-player whose test results are not yet available. Last year, UCLA tested five other former players and diagnosed all five as having signs of CTE, marking the first time doctors found signs of the crippling disease in living former players.

CTE is indicated by a buildup of tau, an abnormal protein that strangles brain cells in areas that control memory, emotions and other functions. Autopsies of more than 50 ex-NFL players, including Hall of Famer Mike Webster and perennial All-Pro Junior Seau, who committed suicide last year, found such tau concentrations.

Tony Dorsett, who rushed for more than 12,000 yards with the Dallas Cowboys, was told Monday that he's been diagnosed with signs of chronic traumatic encephalopathy, or CTE. AP Photo/Martha Irvine

Researchers told "Outside the Lines" that they notified Dorsett by phone Monday that they had diagnosed him as having signs of the neurological disease. Dorsett, in an appearance Wednesday afternoon on ESPN's "Dan LeBatard Is Highly Questionable" show, acknowledged he had been tested at UCLA and received results: "I'm not going to say too much more about it ... I'm trying to be proactive rather than reactive."

Two weeks ago, upon arriving in California for his evaluation and brain scan at UCLA, Dorsett described to "Outside the Lines" the symptoms that compelled him to seek testing: memory loss, depression and thoughts of suicide.

The former Cowboys running back, now 59, said that when he took his Oct. 21 flight from Dallas to Los Angeles for testing, he repeatedly struggled to remember why he was aboard the plane and where he was going. Such episodes, he said, are commonplace when he travels.

Dorsett said he also gets lost when he drives his two youngest daughters, ages 15 and 10, to their soccer and volleyball games.

"I've got to take them to places that I've been going to for many, many, many years, and then I don't know how to get there," he said.

The 1976 Heisman Trophy winner and eighth all-time leading NFL rusher said he has trouble controlling his emotions and is prone to outbursts at his wife and daughters.

"It's painful, man, for my daughters to say they're scared of me." After a long pause, he tearfully reiterated, "It's painful."

Dorsett said doctors have told him he is clinically depressed.

"I've thought about crazy stuff, sort of like, 'Why do I need to continue going through this?'" he said. "I'm too smart of a person, I like to think, to take my life, but it's crossed my mind."

CTE is a disease with no known cure, but Dorsett said he was seeking answers to explain his cognitive and emotional difficulties.

"I want to know if this is something that has come about because of playing football," he said.

Dorsett's 12-year playing career ended a quarter-century ago. He said he doesn't know how many concussions he suffered, but that they were numerous and he believes their consequences are, too.

"My quality of living has changed drastically and it deteriorates every day," he said.

Researchers involved in the UCLA testing say their brain scan uses a radioactive marker to identify the signs of CTE in the living, as was done with the eight former players. The research team, in affiliation with a company named TauMark, includes: forensic pathologist Bennet Omalu, who discovered CTE in football players; UCLA psychiatrist Gary Small and pharmacologist Jorge Barrio; and neurosurgeon Julian Bailes, co-director of the NorthShore Neurological Institute in Evanston, Ill.

Bailes acknowledged that the sample size is small and the testing is in its "very early" stages, but said, "Our preliminary data seems very strong that the areas of the brain and density of the tau signals correlates exactly with what we have found at autopsy."

DeLamielleure, 62, said he never received a concussion diagnosis during his 13-year career as an offensive lineman for Buffalo and Cleveland, but that during games and practices he endured tens of thousands of blows to his head and believes he had at least 100 concussions.