Rosengren S M, Aw S T, Halmagyi G M, Todd N P McAngus, Colebatch J G
UNSW Clinical School and Prince of Wales Medical Research Institute, Randwick, Sydney, NSW, Australia.
J Neurol Neurosurg Psychiatry. 2008 May;79(5):559-68. doi: 10.1136/jnnp.2007.126730. Epub 2007 Aug 31.
Patients with superior canal dehiscence (SCD) have large sound-evoked vestibular reflexes with pathologically low threshold. We wished to determine whether a recently discovered measure of the vestibulo-ocular reflex-the ocular vestibular evoked myogenic potential (OVEMP)-produced similar high-amplitude, low-threshold responses in SCD, and could differentiate patients with SCD from normal control patients.
Nine patients with CT-confirmed SCD and 10 normal controls were stimulated with 500 Hz, 2 ms tone bursts and 0.1 ms clicks at intensities up to 142 dB peak SPL. Conventional VEMPs were recorded from the ipsilateral sternocleidomastoid muscle to determine threshold, and OVEMPs were recorded from electrode pairs placed superior and inferior to the eyes. Three-dimensional eye movements were measured with scleral dual-search coils.
In patients with SCD, OVEMP amplitudes were significantly larger than normal (p<0.001) and thresholds were pathologically low. The n10 OVEMP in the contralateral inferior electrode became particularly large with increasing stimulus intensity (up to 25 microV) and with up-gaze (up to 40 microV). Sound-evoked (slow-phase) eye movements were present in all patients with SCD (vertical: upward; torsional: upper pole away from the affected side; and horizontal: towards or away from the affected side), but began only as the OVEMP response became maximal, which is consistent with the surface potentials being produced by activation of the extraocular muscles that generated the eye movements.
OVEMP amplitude and threshold (particularly the contralateral inferior n10 response) differentiated patients with SCD from normal controls. Our findings suggest that both the OVEMPs and induced eye movements in SCD are a result of intense saccular activation in addition to superior canal stimulation.
上半规管裂（SCD）患者具有声音诱发的前庭反射大且阈值病理性降低的特点。我们希望确定一种最近发现的前庭眼反射测量方法——眼前庭诱发肌源性电位（OVEMP）——在SCD患者中是否也会产生类似的高幅度、低阈值反应，以及能否将SCD患者与正常对照患者区分开来。
对9例经CT证实的SCD患者和10名正常对照者进行刺激，刺激声为500Hz、2ms的短纯音和0.1ms的短声，强度最高达142dB峰值声压级。从同侧胸锁乳突肌记录传统VEMP以确定阈值，从眼睛上下方放置的电极对记录OVEMP。用巩膜双搜索线圈测量三维眼球运动。
在SCD患者中，OVEMP幅度明显大于正常（p<0.001），且阈值病理性降低。随着刺激强度增加（高达25μV）和向上注视（高达40μV），对侧下方电极记录的n10 OVEMP变得特别大。所有SCD患者均出现声音诱发（慢相）眼球运动（垂直方向：向上；扭转方向：上极远离患侧；水平方向：朝向或远离患侧），但仅在OVEMP反应达到最大值时才开始，这与眼外肌激活产生眼球运动从而产生表面电位一致。
OVEMP幅度和阈值（特别是对侧下方n10反应）可将SCD患者与正常对照区分开来。我们的研究结果表明，SCD患者的OVEMP和诱发的眼球运动都是除上半规管刺激外球囊强烈激活的结果。
