Influence of thresholds on amplitudes in vestibular evoked myogenic potentials

To investigate the relationship between the threshold and the interaural amplitude difference ratio (IADR) in cervical vestibular evoked myogenic potential (cVEMP) testing and pursuit the clinical significance of the parameters.

cVEMP responses were recorded while the SCM contraction was controlled using a pressure cuff. The intensities of the sound stimulation decreased from 95 dB n HL by 5 dB, until no responses were evoked. Thresholds, interaural threshold difference (ITD), amplitudes, and interaural amplitude difference ratio at the stimulation of 95 dB n HL were calculated and the relationship between them was examined.

All subjects showed cVEMP responses bilaterally. Thresholds measured were overall 76 dB n HL and most (92%) ears showed the ITD of 0 or 5 dB. The amplitudes of cVEMP responses showed a positive correlation with the sound intensities, and more specifically with the sound intensity above each threshold value. There was no significant difference in IADR values by the ITD.

Based on our study, the ITD is less than 10 dB in most normal subjects and estimation of threshold should be added to cVEMP testing for probing vestibular asymmetry. Getting a threshold might be helpful in determining whether the abnormal interaural amplitude difference ratio is related to the abnormal ITD.