Chronic Traumatic Encephalopathy
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Chronic traumatic encephalopathy (CTE) is a progressive degenerative disease found in individuals who have been subjected to multiple concussions and other forms of head injury. A variant of the condition, dementia pugilistica, is primarily associated with boxing. CTE has been most commonly found in professional athletes participating in gridiron football, ice hockey, professional wrestling and other contact sports, who have experienced head trauma, resulting in characteristic degeneration of brain tissue and the accumulation of tau protein. Individuals with Chronic Traumatic Encephalopathy may show symptoms of dementia such as memory loss, aggression, confusion and depression which may appear within months of the trauma or many decades later.
Several former NFL players have been diagnosed post-mortem with chronic traumatic encephalopathy. Former Detroit Lions lineman and eight-time Pro Bowler Lou Creekmur,  former Houston Oilers and Miami Dolphins linebacker John Grimsley,  former Tampa Bay Buccaneers guard Tom McHale, former Cincinnati Bengals wide receiver Chris Henry, and former Chicago Bears safety Dave Duerson, have all been diagnosed with post-mortem CTE. Athletes from other sports have also been identified as having CTE, such as hockey players Reggie Fleming  and Bob Probert. 
An autopsy conducted in 2010 on the brain of Owen Thomas, a 21-year-old junior lineman at the University of Pennsylvania who committed suicide by hanging himself, showed early stages of chronic traumatic encephalopathy, making him the youngest person -- and the second amateur player -- to be diagnosed with the condition. The doctors who performed the autopsy indicated that they found no causal connection between the nascent CTE and Thomas's suicide. There were no records of Thomas missing any playing time due to concussion, but as a player who played hard and "loved to hit people," he may have played through concussions and received thousands of subconcussive impacts on the brain.