Introduction: Sport related concussion (SRC) is a public health issue. The true incidence of sport concussion is believed to be higher than reported in most studies due to misdiagnosis and under-reporting (1). To safeguard players against the consequences of concussion, the 5th consensus statement on concussion in sport developed comprehensive return to play (RTP) guidelines (2). Progression between RTP stages is based on results from the sport concussion assessment tool (SCAT-5), a standardised questionnaire used to evaluate players suspected of having sustained a SRC (3). However, it remains unknown if the SCAT-5 is accurate in assessing concussed states at days 3-5 post injury. Consequently, combining the SCAT-5 with objective neurophysiological measures may help shed light on the validity of this tool for assessing concussion recovery.
Objectives: The objective of this study was to assess if injury-related alterations in the SCAT-5 are matched by changes in transcranial magnetic stimulation (TMS) derived intracortical inhibition. We hypothesised that neurophysiological measures would take longer to return to normal than recovery assessed by the SCAT-5 following SRC.
Methods: Thirteen male contact sport athletes (20.5 ± 4.5 years), who reported a concussion were recruited from local Rugby and American football clubs. Participants were tested at 4 timepoints throughout the concussion recovery period: within 24h of concussion (day 0), and at 7, 9 and 11 days after concussion. All participants completed the SCAT-5 and underwent TMS to assess cortical silent period duration (CSp), a measure of intracortical inhibition.
Results: After concussion CSp significantly declined from day 0 (122 ± 28 ms) to day 11 (106 ± 15 ms) (F(3,33) = 7.80, p<.001). SCAT-5 measures of symptom number and severity were significantly decreased (symptom number: χ2(3) = 30.44, p<0.01; symptom severity: χ2(3) = 25.75, p <.001) between the day 0 timepoint and each of the other timepoints. SCAT-5 balance errors (mBESS) decreased significantly (F(3,33) = 19.55, p <.001) between the day 0 timepoint and each of the other timepoints. CSp and SCAT-5 recovery patterns were different. SCAT-5 domains recovered faster showing no further significant changes after day 7, whilst CSp was still decreasing between days 7 and 9. Due to the small sample size we also used a Bayesian linear model to investigate the recovery of CSp and mBESS. The posterior distribution of our Bayesian model provided evidence that CSp decreased at day 7 and it continued to decrease at day 9, unlike mBESS which decreased at day 7 and then reached a plateau.
Conclusion: There are clinically important discrepancies between clinical and neurophysiological measures of concussion recovery. This finding has important implications for return to play protocols and the prevention of complications after sport concussion.