Mapping brain recovery after concussion: From acute injury to 1 year after medical clearance
Nathan W. Churchill, PhD, Michael G. Hutchison, PhD, Simon J. Graham, PhD, and Tom A. Schweizer, PhD
Neurology® 2019;93:e1980-e1992. doi:10.1212/WNL.0000000000008523
This study confirms long-term changes in brain function 1-year post “clearance” from concussion. Using multi-method imaging, and comparing to a control group, changes in some brain connectivity were found in the concussed sample. Changes were noted in global connectivity and cerebral blood flow.
The principal finding of this study was that different aspects of brain physiology have different patterns of long-term recovery, with only a subset of MRI parameters showing non-significant concussion effects at 1 year after RTP. For brain function and white matter diffusion anisotropy (a measure of axonal integrity), no significant concussion effects were seen at 1 year after RTP, whereas for CBF and white matter diffusivity (a different measure of axonal integrity), persistent effects were seen at this time. Secondary analyses showed that the effects of concussion on the brain also vary as a function of clinical measures, including acute symptom severity and time to RTP, for all examined MRI parameters.
It is important to note that no subjects were complaining of any problems and had returned to full sports participation. This highlights one of the ongoing questions: what does this mean? Also note that the concussed findings are averaged across all 24 participants. About half had 2 previous concussions and half had only 1concussion. The findings are more specific than previous studies and add important information.
Abstract from Article
Objective. To test the hypothesis that concussion-related brain alterations seen at symptomatic injury and medical clearance to return to play (RTP) will have dissipated by 1 year after RTP.
Methods. For this observational study, 24 athletes with concussion were scanned longitudinally within 1 week after injury, at RTP, and 1 year after RTP. A large control cohort of 122 athletes were also scanned before the season. Each imaging session assessed global functional connectivity (Gconn) and cerebral blood flow (CBF), along with white matter fractional anisotropy (FA) and mean diffusivity (MD). The main effects of concussion on MRI parameters were evaluated at each postinjury time point. In addition, covariation was assessed between MRI parameters and clinical measures of acute symptom severity and time to RTP.
Results. Different aspects of brain physiology showed different patterns of recovery over time. Both Gconn and FA displayed no significant effects at 1 year after RTP, whereas CBF and MD exhibited persistent long-term effects. The effects of concussion on MRI parameters were also dependent on acute symptom severity and time to RTP for all postinjury time points.
Conclusion. This study provides the first longitudinal evaluation of concussion focused on time of RTP and 1 year after medical clearance, using multiple different MRI measures to assess brain structure and function. These findings significantly enhance our understanding of the natural course of brain recovery after a concussion.
Correspondence: Dr. Schweizer at SchweizerT@smh.ca