BACKGROUND: Chronic traumatic encephalopathy (CTE) is the term coined for the 
neurodegenerative disease often suspected in athletes with histories of repeated 
concussion and progressive dementia. Histologically, CTE is defined as a 
tauopathy with a distribution of tau-positive neurofibrillary tangles (NFTs) 
that is distinct from other tauopathies, and usually shows an absence of 
beta-amyloid deposits, in contrast to Alzheimer's disease (AD). Although the 
connection between repeated concussions and CTE-type neurodegeneration has been 
recently proposed, this causal relationship has not yet been firmly established. 
Also, the prevalence of CTE among athletes with multiple concussions is unknown.
METHODS: We performed a consecutive case series brain autopsy study on six 
retired professional football players from the Canadian Football League (CFL) 
with histories of multiple concussions and significant neurological decline.
RESULTS: All participants had progressive neurocognitive decline prior to death; 
however, only 3 cases had post-mortem neuropathological findings consistent with 
CTE. The other 3 participants had pathological diagnoses of AD, amyotrophic 
lateral sclerosis (ALS), and Parkinson's disease (PD). Moreover, the CTE cases 
showed co-morbid pathology of cancer, vascular disease, and AD.
DISCUSSION: Our case studies highlight that not all athletes with history of 
repeated concussions and neurological symptomology present neuropathological 
changes of CTE. These preliminary findings support the need for further research 
into the link between concussion and CTE as well as the need to expand the 
research to other possible causes of taupathy in athletes. They point to a 
critical need for prospective studies with good sampling methods to allow us to 
understand the relationship between multiple concussions and the development of 
CTE.