OTOLITH FUNCTION IN MAN

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Abstract
An otolith disorder is described in a patient with a subluxed stapes footplate. Otoneurological examination, including tympanoscopy, showed that nonphysiological mechanical stimulation of the otoliths by a (pathologically) hypermobile stapes footplate typically manifests with a pattern of sound-induced paroxysms of ocular tilt reaction (OTR), oscillopsia and postural imbalance (otolith Tullio phenomenon). The rare condition of sound-induced otolithic stimulation in an otherwise healthy young man offered a unique opportunity to investigate otolith reflex control of the eye, head and posture in man. Electro-oculographic recordings and special video analysis (time resolution: 1000 images/s) revealed an initial rapid and phasic counterclockwise rotatory upward deviation with a latency of 22 ms, followed by a smaller tonic effect which lasted as long as sound stimulation (480+20 Hz, 95 dB A). Latencies of the otolithic vestibulospinal reflex, recorded using surface EMG during upright stance with the eyes closed, were surprisingly short with activation of the ipsilateral tibialis anterior muscle 47 ms after the stimulus, and of the ipsilateral gastrocnemius muscle after 52 ms. A considerable postural pertubation was measured by means of a Kistler platform, with the shortest latency for displacement of the centre of pressure of 80 ms and a preferred body sway direction from right-backward to left-forward. When the Valsalva manoeuvre was performed, tonic eye movements and oscillopsia were induced opposite in direction to those produced by the sound reflecting a push-and-pull deviation of the otoliths.