Tuning of the ocular vestibular evoked myogenic potential (oVEMP) to air and bone conducted sound stimulation in superior canal dehiscence

Recent studies have demonstrated the frequency selectivity of air-conducted (AC) and bone-conducted (BC) stimuli in eliciting ocular vestibular evoked myogenic potentials (oVEMPs). In this study frequency tuning of the oVEMP was assessed in patients with superior canal dehiscence (SCD) and compared to responses previously reported for healthy subjects. Six (five unilateral) SCD patients were stimulated using AC sound (50 – 1200 Hz) and BC transmastoid vibration (50 – 1000 Hz). Stimuli were delivered at two standardized intensities: one the same as previously used for healthy controls and the other at 10 dB above vestibular threshold (a similar relative intensity to that used in controls). For AC stimulation, SCD patients had larger oVEMP amplitudes across all frequencies tested for both stimulus intensities. Normalized tuning curves demonstrated greater high frequency responses with the stronger stimulus. For BC stimulation, larger oVEMP amplitudes were produced at frequencies at and above 100 Hz using standard intensity stimuli. For the matched intensity above vestibular threshold, enhancement of the oVEMP response was present in SCD patients for 500 – 800 Hz only. We conclude that SCD causes greater facilitation for AC than BC stimuli. The high frequency response is likely to originate from the superior (anterior) canal and is consistent with models of inner ear changes occurring in SCD