A Longitudinal Assessment of Structural and Chemical Alterations in MMA Fighters.
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Growing evidence suggests that temporally proximal acute concussions and repetitive sub-concussive head injuries may lead to long-term neurological deficits. However, the underlying mechanisms of injury and their relative time-scales are not well documented in human injury models. The current study therefore investigated whether biomarkers of brain chemistry (MR spectroscopy: N-acetylaspartate, combined glutamate and glutamine, total creatine) and structure (cortical thickness, white matter/sub-cortical volume) differed between mixed martial artists (MMA; N=13) and matched healthy controls without a history of contact sport participation (HC; N=14). A subset of participants (MMA=9; HC=10) returned for follow-up visits, with MMA (N=3) with clinician-documented acute concussions also scanned serially. As expected, MMA self-reported a higher incidence of previous concussions and significantly more cognitive symptoms during prior concussion recovery. Fighters also exhibited reduced memory and processing speed relative to controls on neuropsychological testing coupled with cortical thinning in the left posterior cingulate gyrus and right occipital cortex at baseline assessment. Over a 1 year follow-up period, MMA experienced a significant decrease in both white matter volume and N-acetylaspartate concentration, as well as relative thinning in the left middle and superior frontal gyri. These longitudinal changes did not correlate with self-reported metrics of injury (i.e., fight diary). In contrast, HC did not exhibit significant longitudinal changes over a 4 month follow-up period (p > 0.05). Collectively, current results provide preliminary evidence of progressive changes in brain chemistry and structure over a relatively short time period in individuals with high exposure to repetitive head hits. These findings require replication in independent samples.