Longitudinal white-matter abnormalities in sports-related concussion: a diffusion MRI study of the NCAA-DoD CARE Consortium

Objective To study longitudinal recovery trajectories of white-matter
after sports-related concussion (SRC), we performed diffusion tensor
imaging (DTI) on collegiate athletes who sustained SRC.  Methods
Collegiate athletes (n=219, 82 concussed athletes, 68 contact-sport
controls, and 69 non-contact-sport controls) were included from the
Concussion Assessment, Research and Education (CARE) Consortium. 
The participants completed clinical assessments and DTI at four time
points: 24-48-hours post-injury, asymptomatic state, seven days following
return-to-play, and six-months post-injury.  Tract-based spatial
statistics were used to investigate group differences in DTI metrics and
identify white-matter areas with persistent abnormalities. 
Generalized linear mixed models were used to study longitudinal changes
and associations between outcome measures and DTI metrics.  Cox
proportional hazards model was used to study effects of white-matter
abnormalities on recovery time.  Results In the white matter of
concussed athletes, DTI-derived mean diffusivity was significantly higher
than the controls at 24-48 hours post-injury and beyond the point when the
concussed athletes became asymptomatic.  While the extent of
affected white matter decreased over time, part of the corpus callosum had
persistent group-differences across all the time points.
 Furthermore, greater elevation of mean diffusivity at acute
concussion was associated with worse clinical outcome measures (i.e.,
Brief-Symptom-Inventory scores and symptom-severity scores) and prolonged
recovery time.  No significant differences in DTI metrics were
observed between the contact-sport and non-contact-sport
controls.  Conclusions Changes in white matter were evident after
SRC at six-months post-injury, but were not observed in contact-sport
exposure.  Further, the persistent white-matter abnormalities
were associated with clinical outcomes and delayed recovery time.