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Vestibular-evoked myogenic potential thresholds normalize on plugging superior canal dehiscence

From the Department of Otolaryngology-Head and Neck Surgery (M.S.W., O.A.M., L.B.M., J.P.C.), Johns Hopkins University School of Medicine, Baltimore, MD; Institute of Neurology (M.S.W.), Sobell Department of Motor Neuroscience, University College London, UK; and Institute of Clinical Neurosciences (M.S.W.), University of Sydney, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia.

Address correspondence and reprint requests to Dr. Miriam S. Welgampola, Institute of Clinical Neurosciences, Royal Prince Alfred Hospital, Sydney University, New South Wales, Australia miriam{at}icn.usyd.edu.au

Background: Diagnosis of the superior canal dehiscence syndrome (SCDS) relies on symptoms such as sound- or pressure-induced vertigo or oscillopsia, demonstration of sound or pressure-evoked vertical/torsional eye movements, and the presence of a defect in the bony roof overlying the superior semicircular canal. Lowered thresholds for eliciting vestibular-evoked myogenic potentials (VEMPs) provide additional conformation.

Objective: To examine VEMP characteristics before and after canal plugging for SCDS.

Methods: VEMPs evoked by air- and bone-conducted tones were measured from the sternocleidomastoid muscles (cVEMP) and periocular sites (oVEMP) of 20 normal volunteers, 10 newly diagnosed subjects with SCDS, and 12 subjects who underwent successful superior canal plugging.

Results: In all SCDS ears, thresholds for evoking VEMP using air-conducted tones were pathologically lowered, with average values of 83.85 ± 1.40 dB sound pressure level (SPL) for cVEMP and 85.38 ± 1.32 dB SPL for oVEMP, 20 to 30 dB below those of controls. Successful canal plugging resulted in normal reflex thresholds. For bone vibration, average thresholds in SCDS ears were 114.62 ± 1.54 dB FL (force level) for cVEMP and 116.0 ± 1.52 dB FL for oVEMP, 10 to 20 dB below controls, yet three SCDS ears had normal thresholds.

Conclusions: Ocular and cervical vestibular-evoked myogenic potentials evoked by air-conducted sound are equally useful in the diagnosis and follow-up of superior canal dehiscence syndrome. Stimulus thresholds are consistently lowered upon presentation and normalize after corrective surgery. Thresholds for bone vibration, in contrast, have a lower diagnostic yield.

Abbreviations: FL = force level; SCDS = superior canal dehiscence syndrome; SCM = sternocleidomastoid; SPL = sound pressure level; VEMP = vestibular-evoked myogenic potential; cVEMP = cervical VEMP; oVEMP = ocular VEMP.

Supported by Grant RO1DC 05040 from the National Institute on Deafness and Other Communication Disorders, NIH. M.S.W. received a Garnett Passe and Rodney Williams Memorial Foundation Postdoctoral Fellowship.

Disclosure: The authors report no conflicts of interest.

Received May 15, 2007. Accepted in final form August 20, 2007.