The degenerative brain disease that has besieged the National Football League for two decades with a billion-dollar lawsuit, congressional hearings, an A-list movie and an unrelenting cortege of

Chronic traumatic encephalopathy, or CTE, is a brain disease linked to repeated hits to the head, often seen in military veterans and athletes including football players, hockey players and boxers. It causes symptoms, which usually appear years after the head trauma, including memory loss, mood changes, confusion and trouble thinking clearly.

CTE cannot be diagnosed until the patient has died and their brain examined. But doctors said there are symptoms such as changes in cognition, mood and behavior. The American Brain Foundation said they can include difficulty thinking, short- and/or long-term memory loss, depression, anxiety, paranoia, headaches and suicidal thoughts or behavior.