Neuropsychological, Metabolic, and GABA_AReceptor Studies in Subjects with Repetitive Traumatic Brain Injury

Abstract

Repetitive traumatic brain injury (rTBI) occurs as a result of mild and accumulative brain damage. A prototype of rTBI is chronic traumatic encephalopathy (CTE), which is a degenerative disease that occurs in patients with histories of multiple concussions or head injuries. Boxers have been the most commonly studied patient group because they may experience thousands of subconcussive hits over the course of a career. This study examined the consequences of rTBI with structural brain imaging and biomolecular imaging and investigated whether the neuropsychological features of rTBI were related to the findings of the imaging studies. Five retired professional boxers (mean age, 46.8 ± 3.19 years) and four age-matched controls (mean age, 48.5 ± 3.32 years) were studied. Cognitive-motor related functional impairment was assessed, and all subjects underwent neuropsychological evaluation and behavioral tasks, as well as structural brain imaging and functional-molecular imaging. In neuropsychological tests, boxers showed deficits in delayed retrieval of visuospatial memory and motor coordination, which had a meaningful relationship with biomolecular imaging results indicative of neuronal injury. Morphometric abnormalities were not found in professional boxers by structural magnetic resonance imaging (MRI). Glucose metabolism was impaired in frontal areas associated with cognitive dysfunction, similar to findings in Alzheimer's disease. Low binding potential (BP) of (18)F-flumazenil (FMZ) was found in the angular gyrus and temporal cortical regions, revealing neuronal deficits. These results suggested that cognitive impairment and motor dysfunction reflect chronic damage to neurons in professional boxers with rTBI.

Systematic review on the characterization of chronic traumatic encephalopathy by MRI and MRS

“…Ten studies based on chronic TBI individuals examined a mixed gender experimental group and one did not provide information on the sex of study participants . All studies focusing on contact sports athletes investigated solely male experimental groups, and the two ex vivo studies did not provide any information on gender . Contact sports athletes included soccer players, boxers, American football players, baseball players, and wrestlers.…”

“…The age range of all studies was from school level to retirement age (13.5–74 years). Of all included in vivo studies, 22 used an age‐matched control group . All articles were published between 1994 and 2018.…”

“…Of the studies using contact sports athletes as the experimental group, 10 applied structural MRI sequences . Two, however, did not perform structural MRI group comparisons .…”

“…Furthermore, the Evans index (maximum width of the anterior horns of the lateral ventricles divided by maximal width of the internal diameter of the skull) was significantly higher in the boxers' group. Bang et al investigated if neuropsychological features and imaging findings in retired boxers are associated . T 1 ‐w images were acquired and analyzed by VBM.…”

Pathological correlations between traumatic brain injury and chronic neurodegenerative diseases

“…This damage is frequently mediated by free radicals and reactive oxygen species (ROS) produced from ischemia-reperfusion injury, glutamatergic excitotoxicity, or neuroinflammation [39–41]. Following the initial trauma, axonal damage from the shear forces of primary injury affects membrane permeability and ionic balance [42].…”