What is VEMP (vestibular evoked myogenic potential) testing, and why is it important?
Jill Craig: Vestibular Evoked Myogenic Potentials or VEMP is used to assess the function of the utricle and saccule - the otolithic organs of the peripheral vestibular system. It also complements the information provided by the video head impulse test (vHIT) and other forms of inner ear testing.
Faith Akin: For veterans, VEMP has been used to examine the impact of noise, blast exposure, and traumatic brain injury on the vestibular system. Studies in humans suggest that the saccule may be particularly susceptible to noise or blast related damage1. Emerging evidence suggests that Cervical Vestibular Evoked
Myogenic Potentials (cVEMP) are more likely to be absent in individuals with more severe noise-induced hearing loss than in individuals with mild noise-induced hearing loss2. Similarly, recent studies have demonstrated that absent cVEMPs are prevalent in individuals who experience dizziness or balance problems following a head injury and occur more often than horizontal semicircular canal (SCC) dysfunction3. However, VEMP testing is not just relevant to veterans - this test now allows for a more comprehensive assessment of the vestibular system, which in turn could aid in the diagnosis of patients with a vestibular disorder.
More importantly, although the VEMP is easily recorded using commercially available evoked potential equipment, measurement of sternocleidomastoid (SCM) muscle electromyography (EMG) is necessary to provide valid interaural comparisons of cVEMP amplitude. Lack of EMG monitoring can negatively impact the interpretation of test results and possibly the diagnosis of the patient.
Ian Curthoys: I echo Faith’s points. As scientists, we try to learn more and more about the vestibular system. We focus on learning about structures, their purposes and the impact when that structure does not function properly. We can pass on the important information in papers, at conferences and through work with companies like Otometrics. We learn more and more every day. Over time, we have provided very important evidence that in the end improves patient care. A good example of this is the use of air conducted sound to get Ocular Vestibular Evoked Myogenic Potentials (oVEMP).
The elephant in the room is: how is sound an otolithic stimulus when everything we have been taught tells us that the otoliths sense linear acceleration? Of course, there is no linear acceleration in air conducted sound. But now we know that sound and vibration cause fluid displacement of the endolymph of the inner ear, which deflects these super-sensitive, super-fast type I receptors in the otoliths. So these otolithic receptors are activated by both linear acceleration and by sound and vibration. They don’t just respond to linear acceleration alone.
We study these things to understand just how the system works so it can be tested properly - and this gives VEMP testing a strong scientific basis.
Jill: Up until late 2015, the US Food and Drug Administration (FDA) had not recognized VEMP testing protocols as an approved procedure in the United States. And as of October 2015, the cVEMP and oVEMP tests for the ICS Chartr® EP 200 with VEMP were cleared by the FDA. We are proud to be the first manufacturer who can deliver an EP system with VEMP that is deemed safe and reliable by the FDA. This new development demonstrates that Otometrics is the clinician’s manufacturer – we are dedicated to helping our customers succeed in helping their balance patients obtain a timely and accurate diagnosis. Thank you for your question! You can read more detail in our previous AudiologyOnline interview.