Cervical Evoked Myogenic Potential (cVEMP)

In some years ago, independent evaluation of different parts of the inner ear such as semicircular canals, saccule, and utricle was a dream. The introduction of new tests such as cVEMP, oVEMP and vHIT has made it possible to evaluate the performance of these structures. One of the most useful tests to evaluate the cause of vertigo is the cVEMP test, which examines saccule function in the inner ear.
By presenting high-intensity acoustic stimuli to the ear, a set of reflexes are activated. Since both the vestibular organs (such as the saccule) and the auditory components (such as the cochlea) are located near the stapes, acoustic stimuli may trigger acoustic-motor responses by stimulating each of these regions.
cVEMP reflects the activity of the vestibular system, which is triggered by high-intensity sounds and is recognized as a change in neck muscle potential. This response is recorded as a change in the activity of the SCM muscle after stimulation of the vestibular system with acoustic signals of approximately 90 dB HL and greater. cVEMP represents a vestibuloculic reflex, a rapid reflexive change in muscle tone that stabilizes the head after an unexpected stimulation.
cVEMP is a unilateral response that is detected in the SCM muscle on the same side of the stimulated ear. This response indicates a transient inhibition of SCM muscle activity after saccular acoustic stimulation.
The cVEMP waveform is seen as a biphasic response (positive and negative) in the latency range of 10-25 milliseconds. In short, cVEMP is a vestibular response, not an auditory one. That is, it is recorded in people with profound hearing loss as long as the vestibular function is healthy. In addition, this response can be recorded when the perception of the stimulus is masked by BC noise.
Saccule stimulation produces postsynaptic inhibitory potentials in the cervical muscle neurons. That is, after delivering a high-intensity sound, there is a temporary decrease in muscle activity that is recorded as a positive wave in the cVEMP. The upper part of the vestibular nerve innervates the anterior part of the saccular macula, but the lower part innervates the posterior part. Clinical evidence suggests that cVEMP is dependent on normal vestibular function of the inferior auditory nerve. In mammals, saccule fibers enter the inferior vestibular nucleus, along with fibers from the semicircular canals and utricle. From the inferior vestibular nucleus, cVEMP pathways reach the lateral vestibulospinal pathway to motoneurons in the XI cranial nerve that innervates specific muscles in the neck. The SCM muscle is innervated by the XI cranial nerve.
Any device that has the capability to record middle latency potentials can be used for cVEMP recording. Single-channel devices can be used for cVEMP recording, but with two-channel recording, it is possible to better analyze responses. It is best to have a cVEMP test in a quiet room while the patient is sitting or lying down. In various studies, cVEMP registration has been performed from several locations including:
– Recording in Vertex and Inion
– Recording in Trapezius muscle
– Recording in SCM muscle
– Recording in the head splenium muscle
– Recording from hands and feet
– Recording from post-auricular muscle