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Introduction

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Sudden, complete unilateral loss of vestibular function in normal, healthy individuals results in a dramatic series of symptoms—strong sensations of turning (vertigo), nausea, rapid eye movements (nystagmus), oscillopsia (the illusion that the visual world is moving as they move their head), falling to the affected side, gait ataxia, postural instability, distortions in the perception of body orientation and movement, and inadequate compensatory responses to head movement. We will use the term unilateral vestibular deafferentation (UVD) syndrome to refer to these symptoms. Such patients are greatly distressed. Over the first few days most of the symptoms decline and the patient's distress correspondingly diminishes. For most patients, these symptoms have disappeared within a few weeks, and the patients return to their normal lifestyle and are happy with their recovery. The term used to describe that general recovery is vestibular compensation, and superficially it seems that there is a full recovery and vestibular function has returned. Indeed, in a few patients this is exactly what does happen: some patients with vestibular neuritis experience all these symptoms, but as their vestibular neuritis diminishes, their peripheral vestibular function, as shown by new specific, objective tests, is completely restored. However, in most patients there is little or no restoration of vestibular function, and when their peripheral vestibular function is tested by these new tests of canal and otolith function, the permanent loss is clearly shown. Nevertheless, most patients with permanent UVD recover and are happy—they are “well-compensated.” They do not experience vertigo, nausea, oscillopsia, or postural unsteadiness (see Box 8-1).

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Box 8-1 ABBREVIATION GLOSSARY

  • ABR — auditory brainstem response

  • BVD — bilateral vestibular deafferentation

  • contralesional — on the opposite side to the affected ear (i.e., the healthy side)

  • COR — cervical ocular reflex

  • cVEMP p13 — the initial positivity at 13 msec of the cervical vestibular evoked myogenic potential

  • GABA — gamma-amino-butyric acid

  • ipsilesional — on the same side as the affected ear

  • LVN — lateral vestibular nucleus

  • MVN — medial vestibular nucleus

  • OCR — ocular counterrolling

  • OTR — ocular tilt reaction

  • oVEMP n10 — the initial negativity at 10 msec of the ocular vestibular evoked myogenic potential

  • pitch — rotation around the interaural axis of the head

  • roll — rotation around the naso-occipital axis of the head

  • SVH — subjective visual horizontal

  • SVV — subjective visual vertical

  • UVD — unilateral vestibular deafferentation

  • VEMP — vestibular evoked myogenic potential

  • VOR — vestibulo-ocular reflex

  • yaw — rotation around the vertical axis of the head

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That the objective tests show the permanent vestibular loss implies that well-compensated patients must have developed some means of overcoming the loss of this major sensory system. The big question is how? What are these patients doing to help themselves so much? This puzzle is sharpened by the fact that some patients, after apparently identical vestibular loss, continue to complain about their UVD syndrome for years after the event, and are so unhappy they repeatedly visit their clinician ...

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