EMG Normalization Eliminates cVEMP Amplitude Asymmetries in Normal Subjects

Abstract

The cervical vestibular myogenic potential (cVEMP) is a sound-evoked sonomotor response that can be recorded from the sternocleidomastoid (SCM) muscles in the neck. There is general agreement that the cVEMP provides information about the integrity of the saccule and/or inferior vestibular nerve. Since the amplitude of the cVEMP is correlated with the degree of tonic activation, the level of EMG can influence interaural asymmetries and lead to possible misdiagnoses of unilateral impairment. Thus, amplitude correction, or normalization, was created as a mathematical process to remove the influence of EMG on cVEMP amplitudes. Therefore, the purpose of this investigation was to determine whether the use of amplitude correction techniques would reduce significantly the P13-N23 interaural amplitude asymmetry data in otologically and neurologically intact adults when the level of EMG was varied. Participants included 20 adults, age 21-29. cVEMP testing was completed using EMG target levels ranging from 100 to 400 μV. Results indicated that statistically significant EMG level-dependent differences in cVEMP amplitude disappeared after amplitude normalization was applied. No significant differences in mean amplitude were observed between 300-400 μV EMG target levels though significant differences in EMG existed. The results of this study support the use of amplitude normalization to reduce the statistical upper limits of cVEMP interaural asymmetry measurement variables.