The role of chronic traumatic encephalopathy on amyotrophic lateral sclerosis
Steen, Andrea Lee
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It has been postulated that there could be a connection between traumatic brain injury (TBI) and motor neuron disease (MND), including amyotrophic lateral sclerosis (ALS). As chronic traumatic encephalopathy (CTE) is caused by repeated TBI and is a newly examined disease, there has been little evaluation of the potential relationship between CTE and ALS. It was proposed that CTE is a risk factor for not only MND, but also ALS. There is significant evidence that even a single TBI is a risk factor for Parkinson's disease (PD), thought to be invoked by the inflammatory process that the brain undergoes following a TBI. General rigorous physical activity with trauma to the trunk or extremities does not appear to be a risk factor for ALS. However, physical activity with associated head traumas, especially repeated head traumas, does seem to increase the likelihood of developing ALS. The biological mechanism for this is suspected to be increase in free radicals during exercise in individuals who are predisposed to decreased antioxidant function. Additionally, individuals who have suffered repeated head trauma, even amongst the general population in a non-athletic setting, has been shown to drastically increase the individual's chance of developing ALS. CTE, which is most common in athletes, is speculated to be caused by TAR DNA-binding protein 43 (TDP-43), tau neurofibrillary tangle (NFT), and beta-amyloid (A-Beta) protein inclusions in brain tissue following a multitude of TBI during high level sport activity. There are individuals who suffer initially CTE, followed by ALS, indicating CTE is clearly a risk factor for ALS. Anatomically, the TDP-43, NTF, and A-Beta; inclusions are present in the brain tissue of both individuals with CTE alone as well as the individuals with CTE and ALS. The anatomic difference between these two pathologies is the inclusion of these three proteins in the spinal cord of ALS patients as well. Unfortunately, there are indications that previous studies of professional athletes and their development of ALS have presented with significant issues including confounding factors of the subpopulation and sample sizing. Additionally, the anatomical cause of TBI leading to ALS is still unknown. Further evaluation on the relationship between head injury and ALS must be dedicated to investigating the mechanism involved in developed PD versus ALS following TBI. The biologic sequence following TBI that leads to ALS must be examined and compared to individuals whom develop ALS but did not suffer TBI. Moreover, an assessment must be made to determine what causes some individuals to develop protein inclusions solely in the brain tissue, leading to CTE, and some individuals to have an advancement of the protein inclusions into the spinal cord, leading additionally to CTE followed by ALS.