Athletes may be returning to play sooner than they should. Detailed scans of concussed University of British Columbia hockey players found that the protective fatty tissue surrounding brain cell fibres was loosened 2 weeks after an injury, even though athletes felt fine and were deemed ready to return to the ice. The loosening of myelin slows the transmission of electrical signals between brain cells. Researchers previously showed in animals that this loosened myelin can completely deteriorate with subsequent blows—a condition that resembles multiple sclerosis.

This is the third study arising from the before-and-after study of 45 UBC hockey players. The athletes had their brains scanned with MRI before the season began; if they were concussed, they were rescanned 3 days afterward, 2 weeks afterward, and 2 months afterward. Eleven athletes were concussed during the season, and most of them underwent the additional MRI scans.

Conventional MRI imaging done in hospitals to assess brain injury does not reveal myelin loosening. Alex Rauscher, an associate professor in the Department of Pediatrics and the Canada Research Chair in Developmental Neuroimaging, and postdoctoral research fellow Alex Weber, used advanced digital analysis of the scans, using a UBC-developed, pixel-based statistical analysis to find changes that visual inspection could not reveal.

Previous analysis of the concussed athletes’ scans, published by Rauscher in 2016, showed changes to the myelin in the corpus callosum, most susceptible to damage from sudden collisions against the interior of the skull, but researchers didn’t know whether the myelin was diminished, akin to multiple sclerosis, or altered in another way. In this recent study it was revealed that the loosening around the nerve fibres that connect brain cells was temporary, and the myelin had returned to normal when the concussed players were rescanned 2 months after their concussions.

The findings provide a convincing reason to keep concussed athletes on the bench even if they no longer exhibit any symptoms, as measured by a standard test of cognitive abilities, balance, coordination, and mood. Passing a concussion test may not be a reliable indicator of whether the brain has truly healed, and more waiting time may be advisable to prevent long-term damage.

The study “Pathological insights from quantitative susceptibility mapping and diffusion tensor imaging in ice hockey players pre and post-concussion,” is published in Frontiers in Neurology.