The clinical reliability of vestibular evoked myogenic potentials

Vestibular evoked myogenic potential (VEMP) testing has gained popularity as a diagnostic modality in otolaryngology and audiology. To maximize the utility of this test, examiners need the availability of ideal test settings and reliable norms. We conducted a prospective study of 8 subjects with no history of neurotologic symptoms to examine the test-retest consistency of VEMP testing and to analyze the impact of stimulus type and muscle tension monitoring. All subjects underwent VEMP testing with two stimuli: a 500-Hz tone and a click. With each stimulus, testing was completed with and without monitoring of sternocleidomastoid muscle tension. All subjects participated in an initial testing session and then returned for a repeat testing session 2 to 4 weeks later. We measured the amplitude of primary waveforms P13 (first positive peak) and N23 (first negative peak) and analyzed the reliability and reproducibility of the mean amplitude asymmetry of these VEMP peaks. The P13 component of the VEMP (specificity: 86.25%) demonstrated a more stable amplitude than did the N23 component (specificity: 70.50%). Therefore, our statistical analysis of the effect of stimulus type and muscle tension monitoring on test-retest reliability was limited to the P13 waveform. We found that neither the type of stimulus nor the presence or absence of muscle tension monitoring had any statistically significant effect on amplitude asymmetry. We concluded that in VEMP testing, the P13 component was more specific than the N23 component in identifying normal subjects and that the P13 component provided consistent results across test sessions, regardless of the type of stimulus or the presence or absence of muscle tension monitoring.