A comparison of contralateral acoustic suppression of transient-evoked otoacoustic emissions measured in a group of individuals at risk of mild traumatic brain injury through participation in contact sports and a group of controls.

This small scale preliminary study aims to assess whether athletes participating in sports with a high occurrence of sub-concussive injury present with reduced contralateral acoustic suppression (CAS) of transient-evoked otoacoustic emissions (TEOAEs). CAS TEOAEs has potential to be used as an objective assessment of concussion, either at the “pitch-side” or as part of a “return-to-play” protocol. Previous studies have shown reduced CAS TEOAEs in subjects experiencing auditory symptoms post-concussive injury (e.g. Nölle et al, 2004). However, the effect of repeated sub-concussive injuries on CAS TEOAEs in participants with no auditory symptoms is less well understood, though it has important implications for the use of CAS TEOAEs in sports-related concussion assessment. CAS TEOAEs was measured in accordance with the test paradigm described by Hood et al (1996). TEOAEs were recorded in response to 60 dB p.e. SPL clicks with and without a 65 dB SPL broadband noise presented to the contralateral ear. Measurements were made from both ears of nine athletes who regularly play sport with a high occurrence of sub-concussive injury and fifteen control subjects who had not previously played such sports. For each subject four CAS TEOAEs measurements were obtained. These were CAS TEOAEs in the (i) right and the (ii) left ear; (iii) the sum of CAS TEOAEs obtained in both ears; and (iv) the magnitude of the difference in CAS TEOAE between the right and left ears. Results showed no significant difference between the athlete and control group for all four measures of CAS TEOAEs. In addition, results showed large inter-subject variability in CAS TEOAEs in both groups. These preliminary findings have implications for the application of CAS TEOAEs in the assessment of sports-related concussion. First, CAS TEOAEs does not appear to be sensitive to cumulative sub-concussive injury, and second, the use of individual baseline measurements is indicated, rather than population-based normative data.