TGIF Dear friends
Welcome back to our TGIF Dr Euan Blogpost!
This week, we are delighted to welcome Ms Christel Chue, an audiologist from Hearing Partners to share her knowledge on Navigating Vestibular Tests: VHIT, cVEMPs, oVEMPs, VNG, and Rotatory Chair Testing for a Comprehensive Balance Assessment.
Dizziness and balance issues can be troubling and unsettling, affecting our daily life and well-being. For anyone experiencing these symptoms, it is crucial to assess your dizziness accurately to facilitate effective communication with your ENT specialist.
Start by describing your symptoms—whether it’s vertigo (a spinning sensation), light-headedness, imbalance (a sense of unsteadiness), or oscillopsia (objects appearing to move when you are still).
Identify any triggers such as head movements, position changes, or specific environments, and note the duration and frequency of your episodes. Also, observe if there are associated symptoms like hearing loss, visual changes, migraine or neurological signs.
These details can guide your specialist in choosing the most appropriate vestibular tests for your condition, making the diagnostic process more targeted and efficient.
Today, we will explore together the fascinating world of vestibular tests essential for diagnosing and managing balance disorders. Understanding these tests can help us appreciate the complexity of our vestibular system and how such diagnostic tools can help in assessing our balance health.
The Vestibular System
Nestled within the inner ear, the vestibular system is our body's own built-in balance mechanism. It comprises several intricate structures, each playing a crucial role in maintaining equilibrium:
Semicircular Canals: These fluid-filled tubes detect rotational movements of the head in three planes: horizontal, vertical, and oblique. The semicircular canals work in tandem to sense angular accelerations and decelerations, helping us maintain stability during activities like turning or looking up and down. Acute dysfunction of just one canal can cause a mismatch in vestibular signals from the two ears, presenting itself as vertigo.
Otolith Organs (Utricle and Saccule): Positioned adjacent to the semicircular canals are the otolith organs—the utricle and saccule. These structures detect linear accelerations and head tilts, providing vital information about changes in head position relative to gravity. The utricle primarily senses horizontal movements like in a car or travellator, while the saccule detects vertical movements like when you take the lift up/down. Acute dysfunction of the otoliths may contribute to imbalance, drop attacks, swaying and motion sensitivity.
Vestibular Diagnostic Assessments
Video Head Impulse Test (vHIT)
vHIT primarily assesses the function of all 6 semicircular canals—the dynamic detectors of rotational head movements. When the head rotates, the fluid within the semicircular canals moves, stimulating hair cells that send signals to the brain about head motion. In response to the head movement, our eyes move in the opposite direction to keep our vision steady and this reflex is known as the vestibulo-ocular reflex (VOR). VHIT captures the velocity of these rapid eye movements and any compensatory eye movements, providing valuable insights into the integrity of the VOR.
2. Cervical Vestibular Evoked Myogenic Potentials (cVEMPs)
cVEMPs target the otolith organs, specifically the saccule, which detects linear accelerations and head tilts in the vertical plane. During cVEMP testing, the contraction of neck muscles in response to auditory stimuli reflects the saccular function. Abnormal cVEMP responses may indicate Superior Semicircular Canal Dehiscence (SSCD) or disorders affecting the saccular and/or inferior vestibular nerve pathway.
3. Ocular Vestibular Evoked Myogenic Potentials (oVEMPs)
oVEMPs focus on the utricle, the otolith organ responsible for detecting horizontal head movements. By measuring eye muscle responses to auditory stimuli, oVEMPs provide insights into the utricular and/or superior vestibular nerve function and help diagnose vestibular disorders associated with SSCD or horizontal acceleration and deceleration.
4. Videonystagmography (VNG)
VNG is a comprehensive diagnostic tool used to evaluate the function of the peripheral and central
vestibular pathways by recording eye movements in response to various stimuli. It involves a series of
tests designed to assess different aspects of balance function:
a. Ocular Motor Testing: This part of the VNG evaluates the presence of spontaneous and
gaze-evoked eye movements, how well the eyes track and follow visual targets, and the
ability of fixate on a visual stimulus. This helps identify abnormalities in the central
vestibular pathways.
b. Positional Testing and Dix-Hallpike Maneuver: These tests examine if changes in head and body positions trigger any abnormal eye movements and dizziness. The patient is placed in different positions (e.g., supine, left or right directions), and the eye movements are monitored in darkness. This helps to detect the most common cause of acute and episodic vertigo – Benign Paroxysmal Positional Vertigo (BPPV).
c. Caloric Testing: Caloric testing assesses the function of the horizontal semicircular canals by introducing warm or cold air or water into the ear canal. The temperature change stimulates the inner ear, causing the fluid in the organ to move and induce involuntary eye movements. This test helps to determine if there is a difference in vestibular function between the two ears – Caloric test is the gold standard test for diagnosing unilateral lateral semicircular canal weakness.
5. Rotatory Chair Testing
Rotatory Chair Testing evaluates the function of the horizontal semicircular canals by analyzing the VOR in response to rotational movements. For this test, the patient sits in a motorized chair that rotates at various speeds and directions while the patient’s eye movements are recorded to assess the peripheral vestibular response, central velocity storage mechanism and presence of central compensation. \
This test is more comfortable than caloric testing for patients as the speeds of rotation are similar to that of natural head movements. Rotatory chair is also the gold standard test for diagnosing bilateral vestibular loss, without the need for ice water irrigation like in caloric testing which can be very uncomfortable for patients.
Apart from bilateral vestibular loss, Rotatory Chair Testing is valuable in diagnosing conditions like unilateral vestibular hypo-function, central vestibular disorders, migraine, and motion intolerance. During the process of treatment, rotatory chair testing can also be repeated to evaluate the effectiveness of vestibular rehabilitation therapy.
Conclusion
In summary, our vestibular system assimilates and processes a symphony of sensory inputs to maintain our balance and spatial orientation. Through advanced tests like VHIT, cVEMPs, oVEMPs, VNG, and Rotatory Chair Testing, we can unravel the complexities of this system, diagnose abnormalities, and guide effective treatment strategies to restore balance.
Apart from selected government-restructured hospitals, Hearing Partners is the only private entity to be fully equipped with such advanced vestibular diagnostic equipment. These assessments are conducted by qualified audiologists in all 4 Hearing Partners diagnostic clinics at: Camden Medical Center, Farrer Park Hospital, Lucky Plaza and Royal Square Novena – except Rotatory Chair testing which is unique to the Camden Medical Center and Lucky Plaza branches.
Well, I do hope this blog post has provided you with some useful information on navigating vestibular tests. If you require an audiologist or would like to consult an ENT specialist about your dizziness, vertigo, or related issues, please contact Christel at Hearing Partners at 6351 9451 and us at Euan's Euan's ENT Surgery & Clinic. You can also contact us at 6694 4282 to schedule a consultation.
For those keen to research and learn more about balance/vestibular testing, here are some useful references you can look up! Have a restful and balanced weekend!
References:
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