Clinical Aspects of Otolith Organ Disorders

Abstract

Advances in vestibular function testing, particularly the development of vestibular evoked myogenic potentials (VEMP), have enabled assessment of the otolith organ function in clinical settings. Although findings from otolith organ function tests are not currently incorporated into the diagnostic criteria in the International Classification of Vestibular Disorders, recent studies have suggested that physiological characteristics derived from these tests may reflect the pathophysiology of certain vestibular disorders. In the affected ear of patients with Meniere’s disease, a tuning shift is observed in which the optimal VEMP frequency shifts toward higher frequencies, and this phenomenon has been shown to be associated with endolymphatic hydrops. In vestibular migraine, the rate of oVEMP abnormalities is significantly higher in definitively diagnosed cases than in probable cases, suggesting that dysfunction of the utriculo-ocular reflex pathway may become more apparent as the clinical phenotype becomes more clearly expressed. Furthermore, selective dysfunction of the otolith organs despite normal semicircular canal function has attracted increasing attention. This condition has been categorized as isolated otolith dysfunction (iOD), and efforts are underway to establish diagnostic criteria. Definite iOD is defined by the coexistence of laboratory evidence of abnormal otolith organ function and preserved semicircular canal function, together with symptoms suggestive of otolith organ dysfunction, including “non-spinning,” “translation,” “tilt,” “floating,” and “flipping-over”. Studies have also shown that among patients with abnormal otolith organ function, preserved semicircular canal function, no sensorineural hearing loss, and no established vestibular diagnosis, recurrent rotatory vertigo is the most common clinical presentation.