Chronic Traumatic Encephalopathy in Athletes: Progressive Tauopathy After Repetitive Head Injury

The hippocampus appears to be crucial for long-term episodic memory, yet its precise role remains elusive. Electrophysiological studies in rodents offer a useful starting point for developing models of hippocampal processing in the spatial domain. Here we review one such model that points to an essential role for the hippocampus in the construction of mental images. We explain how this neural-level mechanistic account addresses some of the current controversies in the field, such as the role of the hippocampus in imagery and short-term memory, and discuss its broader implications for the neural bases of episodic memory.

Traumatic brain injury (TBI) is a serious public health problem. Even injuries classified as mild, the most common, can result in persistent neurobehavioural impairment. Diffuse axonal injury is a common finding after TBI, and is presumed to contribute to outcomes, but may not always be apparent using standard neuroimaging. Diffusion tensor imaging (DTI) is a more recent method of assessing axonal integrity in vivo. The primary objective of the current investigation was to characterize white matter integrity utilizing DTI across the spectrum of chronic TBI of all severities. A secondary objective was to examine the relationship between white matter integrity and cognition. Twenty mild, 17 moderate to severe TBI and 18 controls underwent DTI and neuropsychological testing. Fractional anisotropy, axial diffusivity and radial diffusivity were calculated from the DTI data. Fractional anisotropy was the primary measure of white matter integrity. Region of interest analysis included anterior and posterior corona radiata, cortico-spinal tracts, cingulum fibre bundles, external capsule, forceps minor and major, genu, body and splenium of the corpus callosum, inferior fronto-occipital fasciculus, superior longitudinal fasciculus and sagittal stratum. Cognitive domain scores were calculated from executive, attention and memory testing. Decreased fractional anisotropy was found in all 13 regions of interest for the moderate to severe TBI group, but only in the cortico-spinal tract, sagittal stratum and superior longitudinal fasciculus for the mild TBI group. White Matter Load (a measure of the total number of regions with reduced FA) was negatively correlated with all cognitive domains. Analysis of radial and axial diffusivity values suggested that all severities of TBI can result in a degree of axonal damage, while irreversible myelin damage was only apparent for moderate to severe TBI. The present data emphasize that white matter changes exist on a spectrum, including mild TBI. An index of global white matter neuropathology (White Matter Load) was related to cognitive function, such that greater white matter pathology predicted greater cognitive deficits. Mechanistically, mild TBI white matter changes may be primarily due to axonal damage as opposed to myelin damage. The more severe injuries impact both. DTI provides an objective means for determining the relationship of cognitive deficits to TBI, even in cases where the injury was sustained years prior to the evaluation.

We present the second reported case of autopsy-confirmed chronic traumatic encephalopathy in a retired professional football player, with neuropathological features that differ from those of the first reported case. These differing pathological features underscore the need for further empirical elucidation of the pathoetiology and pathological cascades of long-term neurodegenerative sequelae of professional football. A psychological autopsy was performed with the next-of-kin and wife. Medical and hospital records were reviewed. A complete autopsy was accompanied by a comprehensive forensic neuropathological examination. Restriction fragment length polymorphism analysis was performed to determine apolipoprotein-E genotype. Pertinent premortem history included a 14-year span of play in organized football starting from the age of 18 years. The subject was diagnosed with severe major depressive disorder without psychotic features after retirement, attempted suicide multiple times and finally committed suicide 12 years after retirement by ingestion of ethylene glycol. Autopsy revealed cardiomegaly, mild to moderate coronary artery disease, and evidence of acute ethylene glycol overdose. The brain showed no atrophy, a cavum septi pellucidi was present, and the substantia nigra showed mild pallor. The hippocampus and cerebellum were not atrophic. Amyloid plaques, cerebral amyloid angiopathy, and Lewy bodies were completely absent. Sparse to frequent tau-positive neurofibrillary tangles and neuropil threads were present in all regions of the brain. Tufted and thorn astrocytes, as well as astrocytic plaques, were absent. The apolipoprotein-E genotype was E3/E4. Our first and second cases both had long careers without multiple recorded concussions. Both manifested Major Depressive Disorder after retirement. Amyloid plaques were present in the first case and completely absent in the second case. Both cases exhibited neurofibrillary tangles, neuropil threads, and coronary atherosclerotic disease. Apolipoprotein-E4 genotypes were different. Reasons for the contrasting features in these two cases are not clear. Further studies are needed to identify and define the neuropathological cascades of chronic traumatic encephalopathy in football players, which may form the basis for prophylaxis and therapeutics.