Objectives: Because active and tonic sternocleidomastoid (SCM) muscle contraction is essential for recording the vestibular evoked myogenic potential (VEMP), false-negative VEMPs are sometimes encountered in those who cannot sustain SCM muscle contraction by head elevation. Hence, the goal of this study was to investigate whether the effortless head rotation method can replace the head elevation method in eliciting VEMP responses.
Design: Twenty healthy volunteers underwent VEMP testing, using monaural tone burst stimulation. First, the subject was instructed to keep the head elevated in the pitch plane for recording, followed by rotating the head sideways toward one shoulder as head down in the yaw plane for another recording (elevation-rotation sequence). On the next day, VEMP testing was performed in reverse order (rotation-elevation sequence). Twelve patients with cochleo-vestibular disorders were also enrolled in this study and underwent VEMP testing, using the two methods in random order.
Results: In the elevation-rotation sequence for subjects without cochleo-vestibular disorders, the response rate for the elevation method (100%) was significantly higher than the response rate for the rotation method (70%). In contrast, no significant difference existed in the response rate between the two methods in the rotation-elevation sequence (85% versus 88%). Comparison of the response rates for the initial elevation (100%) and initial rotation methods (85%) revealed a significantly lower response rate for the initial rotation method. Mean latencies of the onset waveform and peaks p13 and n23 showed significant differences between the two methods when using the elevation-rotation sequence but no differences on the rotation-elevation sequence. Furthermore, the rotation method displayed significantly smaller amplitude than the elevation method when using the elevation-rotation sequence but no significant difference in amplitude between the two methods when applying rotation-elevation sequence. In 12 patients with cochleo-vestibular disorders, the response rates for the elevation method (67%) and rotation method (58%) were significantly reduced compared with the rates for subjects without cochleo-vestibular pathology. However, when either the elevation or the rotation method response was considered, VEMPs were present in 11 (92%) of the 12 patients with cochleo-vestibular disorders.
Conclusions: The head rotation method may serve as an alternative for eliciting VEMPs in those who cannot sustain SCM muscle contraction by head elevation. However, the lower response rate with smaller amplitude prevents the use of the head rotation method as an initial screening test for VEMPs. We therefore recommend that when VEMP responses cannot be elicited by the head elevation method, the head rotation method should be utilized to reduce false-negative results.