VEMP

Vestibular Evoked Myogenic Potentials (VEMP) is a reliable and non-invasive neurophysiological test that evaluates the functions of the otolith organs in the inner ear—the utricle and saccule. VEMP is divided into two main types: cervical VEMP (cVEMP) and ocular VEMP (oVEMP). cVEMP examines the functions of the saccule via the sternocleidomastoid muscle, whereas oVEMP assesses the functions of the utricle through the responses of the periocular muscles. It provides important information about the vestibular reflex arcs in which the utricle and saccule participate and the functionality of these arcs.

This test, which serves as a differential diagnostic tool, is especially valuable in diagnosing dysfunctions of the vestibular system such as superior canal dehiscence and Ménière’s disease. VEMP, which offers both reliability and patient comfort, holds an important place in the detailed analysis of vestibular system functions in modern medicine.

What Is VEMP and How Does It Work?

VEMP is defined as the neurophysiological responses used to evaluate the functions of the otolith organs in the inner ear—the saccule and utricle. With high-intensity acoustic stimuli, the otolith organs are activated and functional responses are recorded via the corresponding reflex arcs. These responses are used specifically to assess the vestibulo-collic (cervical VEMP or cVEMP) and vestibulo-ocular (ocular VEMP or oVEMP) reflex pathways. A version known as m-VEMP is preferred more in research than in clinical practice.

cVEMP is a method in which the vestibulo-collic reflex connections, which begin in the inner ear and help stabilize head movements, are recorded from the sternocleidomastoid muscle in the neck. Therefore, cVEMP evaluates the functions of the saccule and the inferior vestibular nerve pathway. On the other hand, oVEMP is recorded from the extraocular muscles and allows the assessment of the integrity and function of the utricle and the superior vestibular nerve, i.e. the vestibulo-ocular reflex pathway.

This test begins with high-intensity acoustic stimuli that activate the otolith organs. The stimulus elicits a response in the neural pathways that carry signals from the vestibular system to the muscles. This response is recorded with electrodes and analyzed to provide information about specific regions of the vestibular system.

History of VEMP

The foundations of VEMP were laid in 1964 through the work of Bickford and his team. Researchers determined that the responses recorded from the neck muscles following an acoustic stimulus indicated a vestibular origin. In 1992, Colebatch and Halmagyi confirmed that the saccule can be activated by sound and that the responses recorded from the sternocleidomastoid muscle have a vestibular origin.

In subsequent years, the clinical applications of VEMP expanded, and the test became an important tool in diagnosing disorders such as superior canal dehiscence, Ménière’s disease, and vestibular neuritis. The development of oVEMP further expanded the vestibular test battery by enabling the evaluation of utricular function.

What Different Types of VEMP Tests Are There?

• Cervical VEMP (cVEMP):

cVEMP is a test that evaluates the functions of the saccular macula and the inferior vestibular nerve in the inner ear. With high-intensity acoustic stimuli, saccular afferents are activated and the signals are transmitted to the ipsilateral vestibular nuclei in the brainstem. The inhibitory interneurons emerging from these nuclei then project to the ipsilateral spinal accessory nucleus, producing an inhibitory response in the sternocleidomastoid (SCM) muscle. During the test, the patient is asked to actively contract the SCM muscle, usually by turning the head to the opposite side. The cVEMP response consists of two main peaks, known as p13 and n23, which are recorded from the SCM muscle.

• Ocular VEMP (oVEMP):

oVEMP evaluates the functions of the utricular macula and the superior vestibular nerve. The stimuli cause the utricular afferents to send signals to the ipsilateral vestibular nuclei. These signals then travel via the medial longitudinal fasciculus to the contralateral oculomotor nucleus, activating the inferior oblique muscle. During the test, the patient is usually asked to look upward to activate these muscles. The oVEMP response is characterized by a negative peak (n10) and reflects the activity of the extraocular muscles.

• Masseter VEMP (mVEMP):

mVEMP is a method similar to cVEMP in that it targets saccular function, but it investigates different neural pathways. In mVEMP, the vestibulo-masseteric reflex function between the sound-sensitive saccular hair cells and the trigeminal motor neurons is examined. It is still used more for research purposes, and studies analyzing its clinical role are ongoing.

In Which Conditions Does the VEMP Test Help with Diagnosis?

The Vestibular Evoked Myogenic Potentials (VEMP) test is an important diagnostic tool in the evaluation of various vestibular disorders. This test not only assesses the functions of the otolith organs (saccule and utricle) in the inner ear, but also provides information about the integrity of the vestibular nerves and the function of the reflex arcs. Two conditions, in particular, highlight the clinical value of the VEMP test.

Ménière’s disease, which is characterized by sudden vertigo attacks, hearing loss, tinnitus, and a feeling of fullness in the ear, is one such condition. VEMP tests offer important information in the diagnosis of this disease by evaluating the functions of the otolith organs. Studies have shown that patients with Ménière’s disease frequently exhibit a reduction in cVEMP amplitude and prolonged latency. These findings are especially indicative of dysfunction of the inferior vestibular nerve and the saccule.

Semicircular canal dehiscence syndrome (SSDS) is a condition that typically arises due to thinning or absence of the bone overlying the superior semicircular canal, leading to vestibular and auditory symptoms. In SSDS, low VEMP thresholds are characteristic and significantly aid in the diagnosis. The low VEMP threshold is reported to offer high specificity in the detection of SSDS.

In addition, vestibular neuritis, otolith dysfunctions, and peripheral vestibular disorders are other important conditions that can be evaluated with the VEMP test. Abnormalities in both cVEMP and oVEMP results provide information about the functional integrity of both the vestibular organs and the nerves, thereby supporting the diagnosis.

What Are the Advantages and Limitations of the VEMP Test?

The VEMP test is a reliable method for evaluating the functions of the otolith organs, which are an important component of the vestibular system, in a non-invasive manner. One of its primary advantages is that it is non-invasive; it provides a safe evaluation process without the need for surgical intervention. Because patients generally feel comfortable during the test, its tolerability is high.

When a comprehensive evaluation of the vestibular system is required, the VEMP test plays a complementary role to other vestibular test methods. It is particularly critical in the detection of pathologies such as superior canal dehiscence syndrome by identifying low threshold levels.

However, the VEMP test also has some limitations. The responses can vary between individuals and may be affected by factors such as age, muscle tone, and electrode placement, which can complicate the interpretation of the results. Additionally, in cases of conductive hearing loss, the responses triggered by air-conducted sound may be absent, which limits the test. Patient cooperation is especially important in the cVEMP test to ensure proper muscle contraction, and this can be challenging for some individuals.

Dr. Ody. Emel Uğur

Dr. Audiologist Emel Uğur was born in 1982 in Çanakkale. She specialized in Pediatric Audiology, Otologic Disorders, and Vestibular System Disorders, and served for 15 years at the Istanbul Training and Research Hospital. In 2015, she joined the Acıbadem Healthcare Group. She currently works as an Audiologist at the Acıbadem Altunizade Hospital and also serves as a faculty member and program director in the Acıbadem University Vocational School of Health Services Audiometry Program.