The Paper

The paper I will be discussing today is a review paper (where previous publications on a specific subject are summarised and assessed). The paper in question is A systematic review of potential long-term effects of sport-related concussion. It is written by a large varied group of researchers, predominantly from the USA, but with some researchers from Canada, the UK and Australia. The researchers predominantly come from the fields of Neurology, Neurosurgery and Sports Science.

History behind the paper

Since the 1920's there have been various case studies of boxers in particular that after a long career have been described as having "punch drunk syndrome". In recent years there has been increasing evidence and attention paid to former NFL players exhibiting cognitive decline disproportionate to their age. Autopsy cases on some former players have shown abnormal pathology not expected for people of their age.

This paper therefore looked at previous publications that were original research (written in English) that reported the prevalence/incidence of neurodegenerative diseases in athletes or former athletes who had a history of sports related concussion. 47 publications out of the many thousands that were originally discovered in the search met these criteria.

Aspects of the previous research

The previous research publications looked at brain pathology in different ways, and took into account other factors. Some of these factors and methods are outlined below.

• Subconsussive Head impacts - 5 of the studies looked at blows to the head that did not result in a concussion as there has been significant interest in these as a possible causal factor. Unfortunately access to reliable estimates of these impacts is almost impossible so whilst there are some studies that show differences in brain pathology for collision sports athletes, other factors such as the increased use of alcohol in this cohort are hard to tease apart.
• Neuroimaging Studies - 14 of the studies used neuroimaging techniques to look into these athletes (primarily American footballers and soccer players). These studies used structural imaging, diffusion tensor imaging, magnetic resonance spectroscopy and positron emission tomography and compared generally low numbers of collision athletes to age matched controls.
• Cognitive Functioning - Assessments of the athletes cognitive abilities in relation to the number of concussions showed a relationship in some studies but not others. Some long term studies reporting on death certificates showed higher rates of Alzheimer's and ALS in former athletes.
• Autopsy studies - A number of autopsy studies have shown abnormal accumulations of the protein p-tau in certain parts of the brain along with a reduction in volume of other parts.

Chronic Traumatic Encephalopathy (CTE)

The strength of results in the autopsy studies has allowed criteria to be set for diagnosis of CTE (disease in the brain caused by repeated injury). Since 2015 there is now a guideline for diagnosis based on an established pattern of results primarily centred around the distribution of p-tau in the brain. Unfortunately there is not yet any criteria for diagnosing CTE in a living person that has been validated.

Summary or TL;DR

What are the findings?

• There is emerging evidence that some retired athletes have mild cognitive impairment, neuroimaging abnormalities and differences in brain metabolism disproportionate to their age, however it is far from irreputable.
• Survey studies show that a minority of former collision sport athletes have depression and/or cognitive decline.
• Autopsy cases of former athletes have revealed diverse forms of neuropathology, and there are now preliminary consensus criteria for defining the neuropathology of CTE.
• More research is needed to better understand the incidence and prevalence of CTE pathology, whether neuropathological findings cause specific clinical symptoms, the extent to which the neuropathology is progressive, the clinical diagnostic criteria and other risk or protective factors.