Neurodegeneration and Sport

Abstract

The recent interest in concussion in sport has resulted in significant media focus about chronic traumatic encephalopathy (CTE), although a direct causative link(s) between concussion and CTE is not established. Typically, sport-related CTE occurs in a retired athlete with or without a history of concussion(s) who presents with a constellation of cognitive, mood, and/or behavioral symptoms and who has postmortem findings of tau deposition within the brain. There are many confounding variables, however, that can account for brain tau deposition, including genetic mutations, drugs, normal aging, environmental factors, postmortem brain processing, and toxins. To understand the roles of such factors in neurodegenerative diseases that may occur in athletes, this article reviews some neurodegenerative diseases that may present with similar findings in nonathletes. The article also reviews pathological changes identified with normal aging, and reviews the pathological findings of CTE in light of all these factors. While many of these athletes have a history of exposure to head impacts as a part of contact sport, there is insufficient evidence to establish causation between sports concussion and CTE. It is likely that many of the cases with neuropathological findings represent the normal aging process, the effects of opiate abuse, or a variant of frontotemporal lobar degeneration. Whether particular genetic causes may place athletes at greater risk of neurodegenerative disease is yet to be determined.

Sports-related brain injuries: connecting pathology to diagnosis

“…31 However, studies do suggest that mTBIs are a major risk factor for the development of CTE; therefore, a major research goal must be to integrate relevant diagnostic modalities along the entire brain injury spectrum. This will allow clinicians to use specific imaging findings and biomarker assays to identify early stages of the disease and to track specific parameters over time.…”

Retirement-from-sport considerations following pediatric sports-related concussion: case illustrations and institutional approach

“…To date, the majority of published cases of CTE have occurred in collegiate and professional athletes who have retired from careers in boxing, American football, and hockey; 44,65 however, a limited number of cases of CTE have been also reported among adolescents with a history of repetitive head trauma. 71 While some authors continue to point out the lack of empirical evidence supporting a causal relationship between TBI and CTE, 29,44,94 there does appear to be empirical justification to actively limit individuals' exposure to concussions and subconcussive head injuries during a period of active brain development in children and adolescents.…”

“…68,69 More recently, however, increasing attention has focused on the more serious effects of concussion and subconcussive injuries including abnormalities documented on advanced structural neuroimaging studies and the longterm risk of developing cognitive impairment, mood disorders, and neurodegenerative diseases including chronic traumatic encephalopathy (CTE). 7,29,44,48,49,51,65,70,71,80,94,98,99 To mitigate the risks of more serious brain injury following SRC, experts offer consensus statements containing supervised return-to-play (RTP) guidelines that promote the safe return of athletes to the field of play after concussion symptoms have fully resolved. 4,68,69 These guidelines may reduce the risk of second-impact syndrome, a very rare and poorly defined condition thought to arise from loss of cerebral autoregulation and resultant diffuse cerebral edema.…”

The science and questions surrounding chronic traumatic encephalopathy

“…A review of the criteria proposed by both groups has been performed. 26 Davis and colleagues 17 have challenged the CTE criteria and staging proposed by McKee and colleagues and have presented an alternative interpretation. They interpret Stage I and II CTE to represent normal aging and Stages III and IV to represent a form of FTLD, concluding their review by stating that "there is insufficient evidence to establish a causal relationship between sports participation and the existence of modern CTE."…”

“…They interpret Stage I and II CTE to represent normal aging and Stages III and IV to represent a form of FTLD, concluding their review by stating that "there is insufficient evidence to establish a causal relationship between sports participation and the existence of modern CTE." 17 …”