Tone-induced cervical and ocular vestibular-evoked myogenic potentials: comparing abnormalities in traumatic and non-traumatic vestibular disease

The clinical meaning and significance of OVEMP morphology

PURPOSE

While some OVEMP recordings are morphologically straightforward, some are poor in appearance, which can create a challenge, as they often require a "second look" by another experienced assessor. Even OVEMPs in normal subjects are sometimes poorly formed, but we wondered if the morphological assessment of the OVEMP response might provide some additional diagnostic information.

METHODS

A single experienced assessor evaluated the OVEMP recordings of 60 patients referred sequentially to a tertiary care centre, and categorized them as "easy to assess" (i.e. obvious to a minimally trained assessor) or "difficult to assess", often requiring a second look by another experienced assessor.

RESULTS

In 48 patients, the results were easy to assess (regardless of the actual clinical results) while 12 were classified as "difficult". This figure reflected the rate of morphologically poor responses we found in our population of normative data.

CONCLUSION

Our clinical concern is that many centres have given up relying on OVEMP assessment because the morphology of the wave may be challenging to interpret. OVEMP assessment often calls for a "second look", requiring a collaboration between two experienced assessors. It seems that this feature may not be diagnostically useful and poor OVEMP morphology may present a challenge in interpretation, but this should not be used as a reason to defer OVEMP testing.

A New Perspective to Interpret How the Vestibular Efferent System Correlates the Complexity of Routine Balance Maintenance with Management of Emergency Fall Prevention Strategies

Bipedalism is unique among mammals. Until modern times, a fall and resulting leg fracture could be fatal. Balance maintenance after a destabilizing event requires instantaneous decision making. The vestibular system plays an essential role in this process, initiating an emergency response. The afferent otolithic neural response is the first directionally oriented information to reach the cortex, and it can then be used to initiate an appropriate protective response. Some vestibular efferent axons feed directly into type I vestibular hair cells. This allows for rapid vestibular feedback via the striated organelle (STO), which has been largely ignored in most texts. We propose that this structure is essential in emergency fall prevention, and also that the system of sensory detection and resultant motor response works by having efferent movement information simultaneously transmitted to the maculae with the movement commands. This results in the otolithic membrane positioning itself precisely for the planned movement, and any error is due to an unexpected external cause. Error is fed back via the vestibular afferent system. The efferent system causes macular otolithic membrane movement through the STO, which occurs simultaneously with the initiating motor command. As a result, no vestibular afferent activity occurs unless an error must be dealt with.

Performing and analysing tone-induced cervical and ocular vestibular-evoked myogenic potentials in traumatic and non-traumatic vestibular pathology

OBJECTIVE

This paper discusses our technique of carrying out cervical and ocular vestibular-evoked myogenic potential testing in a single position. The described technique allows for a symmetrical, natural flexion of the neck muscles, which is helpful as many of our patients have suffered traumatic deceleration injures.

METHODS

Patients with suspected vestibular pathology referred by specialists were sequentially assessed in a tertiary referral neuro-otology unit within a teaching hospital using our technique and our previously established normative database. All patients underwent standardised vestibular assessment in addition to cervical and ocular vestibular-evoked myogenic potential assessment. Our normative data are in keeping with that reported by other centres.

RESULTS

Many of the patients had abnormal vestibular-evoked myogenic potentials, which is in line with a history suggesting otolithic disease.

CONCLUSION

Both cervical and ocular vestibular-evoked myogenic potentials offer several parameters for detecting abnormalities. The technique reported enables us to assess patients in an accurate fashion whether or not they have suffered traumatic neck injuries.