Modern chronic traumatic encephalopathy in retired athletes: what is the evidence?

It has been theorized that a career in contact sports may be associated with long-term neurodegenerative changes. This idea dates as far back as the 1920s, was initially reported in boxers, colloquially termed 'punch drunk,' later more formally termed dementia pugilistica (DP), and now coined chronic traumatic encephalopathy (CTE). Despite considerable ongoing interest on this topic, there is so far only limited evidence showing an association between sport-related concussion (SRC) and increased risk for late-life cognitive and neuropsychiatric impairment, with no causality or risk factors yet determined. The modern CTE description is nevertheless proposed as a unique tauopathy with characteristic pathological stages occurring in retired athletes who have experienced previous repetitive brain trauma. This review highlights the principal issues that so far preclude firm conclusions about the association of athletic head trauma and neurodegenerative diseases of any type. We consider alternative interpretations that may contribute to the clinical progressive neurological findings in some athletes and recommend carefully-controlled epidemiological work to overcome current limitations in this area of research and stimulate future research.