Normative data and test retest variability in vestibular evoked myogenic potantials

Vestibular evoked myogenic potentials (VEMP), is an electrophysiological assesment technique based on evaluation of myogenic reflex responses induced by stimulation of peripheral vestibular system. The reflex responses are called cervical VEMP, when they are measured from sternocleidomastoid muscle, on the other hand; They are called oculer VEMP, when they are measured from extraocular muscles. It was indicated that cervical VEMP displays vestibulocollic reflex activation induced by saccule and inferior vestibular nerve; and ocular VEMP displays the vestibuloocular reflex activation. The purpose of this study is to contribute to the standardization by collecting normative data and evaluating test-retest variability of cervical VEMP; and to demonstrate its reliability. In this study, healthy participants were divided into 3 groups of 30 volunteers, according to their age (Group 1: 10-17 years old, Group 2: 18-59 years old, Group 3: above 60 years old). Each was tested twice with a mean interval of 12 days. The tests were performed with stimulus intensities of 80, 85, 90 and 95 dB and 500, 1000 and 2000 Hz tone burst stimuli, using head rotation method. Both ears were tested seperately. When the mean values of testing parameters were calculated, mean value of P1 latency was 18,43±3,09 ms, mean value of N1 latency was 25,77±3,5 ms, mean value of P1-N1 interlatency was 7,34±2,53 ms and mean value of the amplitude values were 32,84±28,81 μV. Among parameters measured in terms of ear sides and genders, no statistically significant difference was determined. When the P1 latency, N1 latency, P1-N1 interlatency and amplitude values of the groups were compared, statistically significant differences indicated the need of definition of the normative data for each age group. Test-retest comparison showed no significant difference in terms of latency and amplitude. In conclusion, this study has shown that cervical VEMP is a repeatable and diagnostically reliable test. For standardization, determination of normative data with consideration of age groups is recommended for each clinic. Due to broad distribution and standard deviation in amplitude values, utilization of latency instead is more convenient.