Worldwide survey on laboratory testing of vestibular function

Background The function of the peripheral vestibular system can nowadays be quantified. The video head impulse test (vHIT) and caloric irrigation are used for the semicircular canals, cervical vestibular evoked myogenic potentials (cVEMP) for the sacculus, and ocular vestibular evoked myogenic potentials (oVEMP) for the utriculus. Because there is no agreement on normal and pathologic values, we performed a worldwide survey. Methods A web-based standardized survey questionnaire was used to collect data on "reference values" and "cutoff" values. Thirty-eight centers from all continents (except Africa) replied. Results "Reference values": vHIT: mean for the vestibulo-ocular reflex gain of the left horizontal canal 0.91 (range: 0.7-1.01) and of the left horizontal canal 0.92 (0.7-1.05); side difference 0.15 (0.25-0.3). Caloric irrigation: mean peak slow phase velocity of caloric-induced nystagmus for warm (44 degrees C) water 18.65 degrees/s (12-30 degrees/s); cold (30 degrees C) water 18.21 degrees/s (10-25 degrees/s). cVEMP: P13-N23 amplitude mean for the lower limit 28.67 mu V (16-50 mu V); upper limit 200 mu V (50-350 mu V). "Cutoff values": vHIT: side difference 0.26 (0.1-0.4), bilateral vestibulopathy <0.61 (0.3-0.8); unilateral vestibulopathy (UVP) <0.68 (0.4-0.8). Caloric irrigation pathologic side difference mean 25.93% (17.7%-40%) or 12 degrees/sec (5-30 degrees/s); side difference UVP 26.73% (20%-40%) or 29.8 degrees/s (5-100 degrees/s). cVEMP: P13/N23 amplitude mean lower cutoff 32.5 mu V (15-50 mu V), mean upper cutoff 125 mu V (50-200 mu V), asymmetry 36.08 mu V (20-50 mu V). Conclusion This worldwide survey showed a large variability in terms of reference and pathologic cutoff values in the 38 centers included. Therefore, standardization of how to achieve these values and agreement on which values should be used is highly warranted to guarantee a high quality of vestibular testing and interpretation of clinical and scientific results.