Demaryius Thomas’s Death Was Caused by Seizure Disorder

Demaryius Thomas, a four-time All-Pro receiver with the Denver Broncos, died of complications from seizures, the medical examiner in Fulton County, Ga., said Sunday.

Thomas died Dec. 9 at his home in Roswell, Ga., less than six months after he retired from the N.F.L. He was 33.

In July, doctors at Boston University who examined Thomas’s brain found that he had C.T.E., or chronic traumatic encephalopathy, the degenerative brain disease associated with repeated head hits. The disease, which can only be posthumously diagnosed, does not cause death. Doctors said they believed Thomas’s seizures were brought on by a 2019 car crash in which his head cracked the windshield and a hydraulic rescue tool was needed to remove him from the vehicle.

Dr. Ann McKee, the neuropathologist who examined Thomas’s brain, said it would have been highly unlikely for C.T.E. to cause his seizures, and Thomas most likely died of suffocation after a seizure.

While the cause of Thomas’s death was officially determined, Bertram Ennett, an investigator in the Fulton County medical examiner’s office, said the manner in which he died was still undetermined.

Thomas’s driver found him lying in the shower in his home, according to Bobby Thomas, Demaryius’s father.

Bobby Thomas and other family members and friends said Demaryius Thomas’s seizures had become more numerous and pronounced in the final year of his life. They attacked with little or no warning and led Thomas to wreck other cars and fall down steps.

At the same time, he suffered from some of the conditions associated with C.T.E., including memory loss, paranoia and isolation. His behavior became increasingly erratic, those closest to him said, and he went long stretches without leaving his home or responding to calls and text messages.

Thomas dealt with headaches during his N.F.L. career, which began in 2010 when he was drafted in the first round out of Georgia Tech. In Super Bowl 50, which concluded the 2015 season, Thomas was leveled by Carolina Panthers linebacker Luke Kuechly during the game and had a headache so bad that he missed most of the parties after the Broncos’ victory.

In 2019, Thomas had been driving 70 miles per hour in a 30 m.p.h. zone in Denver when he lost control and flipped his car multiple times.

Thomas returned to play the 2019 season, his final one, with the Jets, appearing in 11 games. He continued working out in 2020, but stopped training midway through the year because the frequency of his seizures increased. He sat out that season and officially retired in June 2021.

Thomas played 10 seasons in the N.F.L., with the Broncos, the Houston Texans and the Jets, catching 724 passes for 9,763 yards and 63 touchdowns.

In a video announcing his retirement, Thomas said he was still deciding what to do next and looked to build relationships with anyone who could help.

“It ain’t easy leaving football,” he said. “Because that’s my main thing, just trying to find self and put out love.”