[Exploration of the otolith function].

Abstract

The analysis of our vertiginous patients reveals that the likely existence of a pattern of symptoms related to a disturbance of the otolith organ responsible for detection of linear accelerations. Very often otolith pathology affects only certain directions of movement or tilting in relation to gravity. The various tests of the otolith function do not seem to identify all of these otolith deficits. It is possible that each individual test explores only partially the 4 otolith organs. Our otolith tests are still either too general, or, only focused on a part of a multi-directional function (and wrongly emphasizing a partial pathology). Thus, the history remains the finest diagnostic tool. The exploration of the otolith function has improved. These tests are not redundant. The subjective visual vertical tests the otolith function up to the vestibular cortex whilst the off-vertical axis rotation (OVAR) test explores the ocular otolith reflex. The myogenic otolith evoked potentials are saccule-collic. The cerebral cartography shows the various zones of cortical saccular activity and the tilt suppression test explores a reflex involving the cerebellar nodulus. However all of these tests are still nonspecific. There 'non-specificity' is similar to the non-specific nature of a free field hearing or the rotatory vestibular tests. The analysis of patient symptoms, using diagrams summarizing the principal clinical findings, or using a 3D software, facilitates the identification of the involved side, the affected organ (utricle or saccule) and to some extent the possible site of the lesion (just as a visual field would assist in identification of the retinal area affected prior to fundoscopy). Some otolith tests can be very sensitive albeit non-specific like the subjective visual vertical test. Others are more specific in identification of the organ and side affected like the otolith sacculo-collic evoked potentials. The choice of vestibular function tests is best based on the patient's particular symptoms. Thus a patient complaining of falling outwards is to be tested by offset rotations. A patient complaining of falling while going down in a lift is best investigated by the cortical vestibular otolith evoked potentials.