NFL Player Demaryius Thomas' Cause of Death Revealed

The parents of the late Denver Broncos star wide receiver Demaryius Thomas said their son died from cardiac arrest. Bobby Thomas and Katina Stuckey Smith told Good Morning America Tuesday their son's death was caused by a seizure disorder, which lead to cardiac arrest. They also said the 33-year-old suffered from Stage 2 CTE, a degenerative brain disease that can only be diagnosed after death.

Thomas was found unresponsive in the shower at his Roswell, Georgia home on Dec. 9, 2021, just days before his 34th birthday. Reports at the time linked his death to complications from his 2019 car crash. His cousin, LaTonya Bonseigneur, also told the Associated Press in December he "had been suffering from seizures for over a year." Thomas retired in June 2021, following 10 seasons in the NFL.

Stuckey Smith and Thomas donated Thomas' brain to researchers, his family told GMA. "Cardiac arrest, you know, is the way that they're trying to say -- what kinda happened to him," Bobby said, adding that Thomas "suffocated... he died." Stuckey Smith added that Thomas "suffered from CTE stage 2."

Dr. Ann McKee, the director of Neuropathy Core at Boston University, said researchers found "what we've seen in so many other players under the age of 34" in Thomas' brain. "On the basis of multiple lesions in the frontal lobes and temporal lobe are beginning degeneration of deeper areas of the brain. He was diagnosed with CTE. Stage two," McKee explained.

CTE did not cause Thomas' death, but McKee noted that the disease "changes your behavior and your personality." McKee said she has diagnosed CTE (chronic traumatic encephalopathy) in at least 600 athletes after death, and it shows up mostly in cases involving sports with hits to the head.

Thomas was "paranoid" and experienced "memory loss" in the years before his death, Bobby told GMA. The Pro Bowler also complained about having headaches "every single time," Bobby said. Stuckey Smith added that Thomas experienced mood changes and isolated himself. "[Demaryius] would tell me, he was like, 'Mom, I don't know what's goin' on with my body -- I gotta get myself together.' And he said, 'I don't feel like myself anymore,'" Stuckey Smith recalled.

Thomas began experiencing violent seizures, which McKee believes were linked to his car accident and other injuries he suffered off the football field. He struggled to breathe during his seizures, Bobby recalled. "You could hear him say, 'tch-tch-tch-tch,' like the wind tryin' to come out," Bobby said. "They got to the point where he was havin' three or four back to back... If it wasn't for those seizures, he woulda went back playin' football."

After Thomas' death, Stuckey Smith was against donating her son's brain for research. However, she agreed after remembering Thomas once told her that if anything happened to him, he wanted to help other players.

Thomas was born in Montrose, Georgia, and played at Georgia Tech. The Broncos drafted him in 2010 and he spent his first eight seasons with the team. He played in the Broncos' Super Bowl 50 victory in 2016. The Broncos traded him to the Huston Texans, where he struggled with injuries before he was released. In 2019, he signed with the New England Patriots but was traded to the New York Jets before playing a game. He appeared in 11 games in 2019 and did not play in 2020.