CTE is thought to be caused by repetitive brain trauma. It is often found in those who are more likely to get head injuries. In fact, it was once called punch-drunk syndrome or dementia pugilistica. A 1928 study in the Journal of the American Medical Association (JAMA) was the first to describe the condition, which occurred among boxers, according to the Brain Injury Research Institute.
Indeed, boxing and other sports where head injuries are common — wrestling, cheerleading, basketball, soccer, ice hockey, rugby, field hockey, volleyball, lacrosse and football — are often culprits. A 2017 study published in JAMA on 200 deceased football players found that 90 percent of the players had CTE. Of these players, 71 percent of the players had severe CTE.
Other people who may acquire CTE include those who have been physically abused, have epilepsy or who've had traumatic injuries in the military. A 2012 study published in the journal Science Translational Medicine found the disease in the brains of four deceased U.S. military veterans.
"Our study, for the first time, shows military personnel that have experienced blast exposure exhibit CTE that's basically indistinguishable from [the CTE in] the athletes we've looked at," said study researcher Patric Stanton, a cell biology professor at New York Medical College in Valhalla, New York.
How chronic traumatic encephalopathy works isn't completely understood. Experts think that when the brain is injured repetitively, it wastes away, according to the Mayo Clinic. Researchers also think that after a brain injury, a protein called tau forms clumps in the brain, thus killing brain cells, according to the Concussion Legacy Foundation. And, though uncommon, the protein beta-amyloid has also been found in people with CTE.
The damage of CTE often mimics that of Alzheimer's disease. The difference is that the tau protein builds up in the wrinkles of the brain in those affected with CTE, while in those affected with Alzheimer's, the protein is more spread out in the brain.
Currently, CTE can be diagnosed only after a person has died, because an examination of the person's brain is required to make the diagnosis. Because that type of examination can't be performed until the patient is dead, it is hard to know the exact symptoms of the disease. Recently, though, scientists found a new marker for CTE that could help doctors diagnose the condition while a person is still alive.
The symptoms of CTE generally do not show up until years or decades after the brain trauma, according to the Boston University Research CTE Center. This can also make it very hard to link symptoms to CTE.
According to the Mayo Clinic, symptoms of CTE may include the following:
Images of the brains of people who had CTE clearly show holes in the brain.
Because CTE is diagnosed after death, there is really no way yet of diagnosing and treating a person who has this disease. Medical professionals may try neurological, or brain imaging, tests to determine if there has been injury to the brain, but there is no standard way to diagnose CTE in the living.
Prevention seems to be the best course of action. Traumatic brain injury (TBI), or concussions, causes 1.4 million deaths, hospitalizations and emergency department visits each year, according to the Centers for Disease Control and Prevention (CDC). In addition, 1.6 million to 3.8 million sports-and-recreation-related TBIs occur each year.
Dr. Kory Gill, an assistant professor at the Texas A&M Health Science Center College of Medicine and a team physician for Texas A&M University Athletics, told Live Science, "Become familiar with the signs/symptoms of concussions, and if you think you or a teammate has a concussion, speak up."
Gill also pointed out that a law passed in 2009 — the Zackery Lystedt Law — requires school districts and nonprofit organizations using school facilities to adopt policies for the management of concussion and head injury in youth sports.