Sacculo-collic response in otosclerosis and following successful stapes surgery

Vestibular evoked myogenic potentials: past, present and future

Since the first description of sound-evoked short-latency myogenic reflexes recorded from neck muscles, vestibular evoked myogenic potentials (VEMPs) have become an important part of the neuro-otological test battery. VEMPs provide a means of assessing otolith function: stimulation of the vestibular system with air-conducted sound activates predominantly saccular afferents, while bone-conducted vibration activates a combination of saccular and utricular afferents. The conventional method for recording the VEMP involves measuring electromyographic (EMG) activity from surface electrodes placed over the tonically-activated sternocleidomastoid (SCM) muscles. The "cervical VEMP" (cVEMP) is thus a manifestation of the vestibulo-collic reflex. However, recent research has shown that VEMPs can also be recorded from the extraocular muscles using surface electrodes placed near the eyes. These "ocular VEMPs" (oVEMPs) are a manifestation of the vestibulo-ocular reflex. Here we describe the historical development and neurophysiological properties of the cVEMP and oVEMP and provide recommendations for recording both reflexes. While the cVEMP has documented diagnostic utility in many disorders affecting vestibular function, relatively little is known as yet about the clinical value of the oVEMP. We therefore outline the known cVEMP and oVEMP characteristics in common central and peripheral disorders encountered in neuro-otology clinics.

Latent superior canal dehiscence syndrome unmasked by stapedotomy for otosclerosis

OBJECTIVE

This report describes a novel case in which superior canal dehiscence syndrome was unmasked by successful stapes surgery for otosclerosis.

METHODS

Case report and literature review regarding superior canal dehiscence syndrome.

INTRODUCTION

Superior canal dehiscence syndrome is a rare but well described condition in which audiovestibular symptoms are caused by noise or straining. A dehiscence of the superior semicircular canal in the floor of the middle cranial fossa is responsible, and acts as a 'third window' into the inner ear.

CASE HISTORY

A patient with confirmed otosclerosis underwent second-side stapedotomy, with good audiometric outcomes. Unfortunately, surgery was complicated by immediate post-operative vertigo and persistent auditory symptoms. A diagnosis of superior canal dehiscence syndrome was eventually made, on the basis of low threshold vestibular evoked myogenic potentials and characteristic computed tomography findings. Superior canal resurfacing resulted in complete resolution of symptoms.

DISCUSSION

The otosclerotic focus in the oval window prevented the development of symptoms from this patient's superior canal dehiscence syndrome. Surgical stapedotomy created a third window and resulted in immediate post-operative imbalance and auditory symptoms.

CONCLUSION

The diagnosis of superior canal dehiscence syndrome should be considered in patients with persistent audiovestibular symptoms after stapes surgery. High resolution computed tomography of the temporal bone and vestibular evoked myogenic potential testing, if available, are the investigations of choice in confirming the diagnosis.