Properties of 500Hz air- and bone-conducted vestibular evoked myogenic potentials (VEMPs) in superior canal dehiscence.
To compare threshold and amplitude properties for air- (AC) and mastoid bone-conducted (BC) cervical (cVEMP) and ocular (oVEMP) vestibular evoked myogenic potentials in superior canal dehiscence (SCD).



Thirteen patients (53±14yrs) clinically diagnosed with SCD were tested using AC 500Hz sound and BC 500Hz transmastoid vibration. Baseline intensities of 135dBpSPL and 138dBpFL respectively were used and reduced until the response amplitudes were less than 2.5 standard deviations of the prestimulus baseline mean. SCD VEMP amplitudes, response gradients and threshold parameters for the initial peaks for the cVEMP (ipsilateral) and the oVEMP (contralateral) were compared with results for normal subjects over a range of intensities.



Despite higher amplitudes, reflex gradients against intensity for AC and BC cVEMPs were significantly less in SCD than normals (P≪0.001) while AC and BC oVEMP gradients were not significantly different between the groups. Abnormally low thresholds for AC 500Hz were present for 85% of cVEMPs and 62% of oVEMPs. Abnormally low BC 500Hz thresholds were seen for 33% of cVEMPs and 83% of oVEMPs. Amplitudes for AC 500Hz were compared over the 135-105dBpSPL intensity range. The cVEMP showed more pathologically large amplitude responses with the lower stimulus intensities (135dBpSPL: 5%, 105dBpSPL: 100%) whereas the oVEMP demonstrated high rates of amplitude increases for all intensities (129-111dBpSPL: 92%). The pattern of pathologically large amplitudes evoked by BC 500Hz was similar for both reflexes such that both cVEMPs and oVEMPs showed maximum prevalence of abnormally large responses around 117dBpFL (cVEMP: 58%, oVEMP: 83%).



In SCD, both AC and BC evoked cVEMPs show evidence of saturation but this is not evident for oVEMPs. Both cVEMPs and oVEMPs show frequent abnormalities of amplitudes and thresholds in SCD compared to normal subjects but the sensitivities differed between measures.



Previous evidence of saturation of cVEMP responses in SCD was confirmed. For diagnosis, AC cVEMP amplitudes at 105dBpSPL or AC-evoked oVEMP amplitudes both have over 90% sensitivity in separating SCD from normal responses.
Prince of Wales Clinical School and Neuroscience Research Australia, University of New South Wales, Randwick, Sydney, NSW 2031, Australia.
Sendhil
S
Govender
Prince of Wales Clinical School and Neuroscience Research Australia, University of New South Wales, Randwick, Sydney, NSW 2031, Australia.
Tavish
T
Fernando
Prince of Wales Clinical School and Neuroscience Research Australia, University of New South Wales, Randwick, Sydney, NSW 2031, Australia.
Danielle L
DL
Dennis
Royal Prince Alfred Hospital, Department of Neurology, Missenden Rd., Camperdown, NSW 2050, Australia; Central Clinical School, University of Sydney, Sydney, NSW 2006, Australia.
Miriam S
MS
Welgampola
Prince of Wales Clinical School and Neuroscience Research Australia, University of New South Wales, Randwick, Sydney, NSW 2031, Australia. Electronic address: j.colebatch@unsw.edu.au.
James G
JG
Colebatch
D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012018:Reflex; D012665:Semicircular Canals / Q000503:physiopathology*; D015837:Vestibular Diseases / Q000503:physiopathology*; D058585:Vestibular Evoked Myogenic Potentials
Superior canal dehiscence, SCD; Vestibular reflexes; cVEMP; oVEMP