Modifications neurométaboliques et microstructurales à la suite d'une commotion cérébrale chez les athlètes féminines

The presence of short and long-term alterations following a sports-related concussion has been detected using advanced neuroimaging methods. Using Diffusion Tensor Imaging (DTI) and Magnetic Resonance Spectroscopy (MRS), alterations of white matter integrity and cellular metabolism have been revealed, respectively. These brain anomalies were detectable in male athletes a few days after a head injury and persisted when athletes were re-evaluated six months post-concussion. However, no study has evaluated the neurometabolic and microstructural effects in the acute and chronic phases of a concussion in female athletes, despite increased susceptibility in women to suffer this type of injury, and a higher number of post-concussion symptoms and rehabilitation time when this injury occurs. Thus, the studies comprising the present thesis aim to document the neurometabolic and microstructural profiles of female concussed athletes using DTI and MRS. The first study evaluated neurometabolic changes in the corpus callosum of male and female hockey players during a university season. Athletes who suffered a concussion were also assessed 72 hours, 2 weeks and 2 months after the head injury in addition to pre- and post-season evaluations. Results showed no difference between athletes who suffered a concussion and control athletes. Furthermore, no difference between pre- and post-season was observed in male athletes, while a decrease in NAA was found in female athletes, suggesting an impact of subconcussive hits to the head. The second study, which used DTI and MRS, revealed alterations in asymptomatic female concussed athletes evaluated an average of 18 months post-concussion. More specifically, MRS revealed a decrease in myo-inositol (mI) levels in the hippocampus and the primary motor cortices (M1) while DTI showed an increase in mean diffusivity (MD) in several white matter tracts. In addition, a region of interest approach of the corpus callosum showed decreased fractional anisotropy (FA) in the segment containing fibers projecting to M1. The third article evaluated athletes who suffered a concussion in the days following head injury (7-10 days) and six months post-concussion using MRS. In the acute phase, neuropsychological alterations and a higher severity of post-concussion and depressive v symptoms were found in concussed athletes relative to controls, but showed recovery in the chronic phase. In contrast, no neurometabolic differences were found between the two groups in the acute phase. In the chronic phase, concussed athletes showed neurometabolic impairments in prefrontal and motor cortices, characterized by a pathological increase of glutamate/glutamine (Glx). Also, a significant decrease in NAA was observed in control athletes at the second time point. Finally, the fourth study aimed to document microstructural alterations within the corticospinal tract and the corpus callosum (CC) of athletes suffering a sport-related concussion six months prior to testing. The analysis showed no difference in the corticospinal tract while several differences were found when segmenting the corpus callosum based on the projections of the callosal fibers. The concussed group had lower MD and lower radial diffusivity (RD) in the region of the CC projecting to the prefrontal cortex, a lower volume of white matter fibers was found in the region projecting to the premotor and supplementary motor areas and a decrease in axial diffusivity (AD) in the region projecting to the parietal and temporal areas was detected. In conclusion, the studies included in this thesis have helped increase knowledge about the neurometabolic and microstructural alterations following a sport-related concussion and showed persistent effects in female athletes. These data are consistent with the literature that suggests concussions are not only causing temporary symptoms.

Keyphrases: sport concussion, traumatic brain injury, female athletes, magnetic resonance spectroscopy, diffusion tensor imaging