Nystagmus induced by bone (mastoid) vibration in otosclerosis: a new perspective in the study of vestibular function in otosclerosis.

BACKGROUND

The aim was to explore vestibular responses to bone vibration-induced nystagmus (BVIN) during bed-side examination in patients with otosclerosis and conductive hearing loss. It is assumed that vibration of the mastoid (at 100 Hz) stimulates all vestibular end organs (semicircular canals and otolith structures). Previous studies described oculomotor responses to vestibular activation by vibratory stimulus. Stimulation of individual semicircular canals produces eye movement in the plane of the stimulated canal. Vibratory stimulation of otolith structures (utricular macula) produces changes in ocular torsional position. Otosclerosis is responsible for conductive hearing loss and symptoms such as dizziness and vertigo. Diagnosis is usually by a combination of family medical history, conductive hearing loss pattern, absence of air-VEMP, and CT scan of the temporal bone.

MATERIAL/METHODS: Eye movements of patients diagnosed with otosclerosis and conductive hearing loss were recorded in complete darkness. These oculomotor responses to long-lasting unilateral vibratory stimulation applied to the mastoid surface were evaluated and the patterns of vertical, torsional, and horizontal eye velocity and eye position were measured by three-dimensional computerized infrared video oculography.

RESULTS

Mastoid vibration evoked responses in all cases, mostly demonstrating excitation of the affected side. In all cases, three-dimensional infrared video oculography showed mostly horizontal nystagmus directed with the slow phase to the healthy side.

CONCLUSIONS

Three-dimensional analysis of BVIN in patients with otosclerosis and conductive hearing loss may be appropriate in evaluating the vestibular function and altered immittance related with this clinical entity. This promises to be an interesting new field of research.