The Dizzy Patient: Objective Measures of the Vestibular System

This blog post is part three of “The Dizzy Patient” blog series. To read part one “Taking a Comprehensive, Yet Concise Case History,” click here. Part two “Things to Know Before Testing” can be found here.

Once you have obtained a detailed case history, it is up to you as the clinician to determine which measures you are going to use for your assessment in a limited amount of time. There are a number of different reasons why a clinician does not perform every test on every single patient – highlighting why clinical decision making is so essential. You must use the patient’s reported symptoms and background information to determine which tests are likely to be the most sensitive to the patient’s potential disorder.

As we all likely learned in our first assessment course, the patient’s reported symptoms should increase an index of suspicion for a certain disorder or condition. For example, if a 70-year old came in for audiologic evaluation and reported recent chemotherapy for breast cancer, you should have an idea of the tests you would like to perform; tests that will lead to an expected outcome. As the patient reports symptoms of vertigo, lightheadedness, and imbalance, a clinical plan should be formed.

There are many vestibular tests available to clinicians today. These particular measures allow for the assessment of all ten vestibular end organs and branches of the vestibular nerve. When choosing a test, it is important to know the anatomy associated with each measure in order to make accurate judgements of vestibular function. Below is a review of commonly used vestibular tests. Let’s go through the purpose of each (with some extra tips from Daniel and Liz):

• Videonystagmography (VNG): evaluation and differentiation between a peripheral and/or central vestibular deficit: ocular motility, positioning/positional testing, and caloric testing.
  • Ocular motility: this portion consists of four subtests of how the eyes move with and without a target
    • Gaze – evaluation of observing any spontaneous eye movement when gazing in certain directions – up, down, left, right (important to perform without fixation if nystagmus is present to help distinguish whether the lesion is central or peripheral)
    • Pursuit – evaluation of how consistently the eye can track a moving target (horizontal/ vertical) without any abnormalities (such as saccadic intrusions)
    • Saccades – evaluation of rapid, conjugate eye movements in response to a randomly moving target

• Positioning/positional testing: evaluation of any abnormal eye movements that are evoked when placed into static and/or dynamic head and body positions
  • Static Positional – evaluation of any abnormal eye movement in the following head positions:
    • Supine (evaluate at a 30 degree angle/caloric position)
    • Head right
    • Head left
    • Body right (like laying on the couch watching TV- typically only completed if nystagmus is present in head right as you’re trying to rule out cervicogenic dizziness)
    • Body left (same as above, except only completed if nystagmus is present in head left)
  • Dynamic Positioning – evaluation of dynamic movement of the patient and used to determine if nystagmus and vertigo can be evoked by rapid head extension to the right, left, or straight back (These are what you use to test for the presence of BPPV)
    • Dix-Hallpike (turn head towards posterior canal of interest [ex: Dix-Hallpike right tests right posterior semicircular canal] and away from anterior canal of interest)
      • There are modifications if your patient has neck issues (cue Side Lying)
    • Deep-Head Hanging (assessment of the anterior canals)

• Caloric testing: evaluation of the horizontal semicircular canal and superior vestibular nerve by introducing a warm and/or cold stimulus via air or water.
  • Monothermal – using one temperature in each ear
    • Most clinics start with the warm temperature first and may stop if it meets their clinical criteria
    • Warm air/water is more provocative than cold!
  • Bithermal – two temperatures (warm and cold) in both ears (a total of at least four irrigations)
  • Visual fixation – gross assessment of VOR suppression (aka when a visual target is present, does the nystagmus reduce or disappear?)

• Rotary Chair: evaluation of the VOR response to a rotational stimulus throughout a certain number of chair oscillations (here’s our old friend, frequency)
  • Common tests on rotational chair
    • Sinusoidal Harmonic Acceleration (street name-SHA) – most commonly used
    • Velocity Step Testing
    • VOR Suppression
  • Stimulus Parameters
    • Frequency – number of oscillations/cycles per second
      • Typical Test Frequencies
        • 01 Hz
        • 02 Hz
        • 04 Hz
        • 08 Hz
        • 16 Hz
        • 32 Hz
      • Velocity – the peak velocity that the chair will reach during each ½ cycle of rotation (½ cycle will consist of an acceleration and deceleration period)
      • Acceleration – the relative speed at which the chair rotates to reach its desired peak velocity at a specific frequency. *Remember, frequency and peak velocity will affect the acceleration (degrees per second^2)*
    • How are we measuring this response?
      Just like with VNG, we are using video goggles to measure this response
    • Three measured parameters during SHA testing
      • VOR Gain – Did the eyes match the magnitude of the physical movement of the chair (equal and opposite 1:1)
      • Phase – Timing relationship between the head rotation and the VOR response
        • Offers great clinical significance – can infer status of compensation
      • Asymmetry – Comparison of the maximum slow phase velocity (SPV) when the patient is rotated clockwise and counterclockwise (aka which directional nystagmus is greater)
    • VOR Suppression: When there is a visual target present during rotation, how much is the patient able to reduce the intensity of their nystagmus?
      *Hint hint* – we should not observe a phase or asymmetry value for this test

• Video Head Impulse Test (vHIT): An objective evaluation of all six semicircular canals in the high frequency region by fast, brief head thrusts. Quick review of one of Ewald’s Laws: the eyes will move in the plane of the stimulated canal. Given that statement, there are inherit pairs of semicircular canals as a result.
  • Lateral (left and right horizontal canals)
  • LARP (left anterior/right posterior canals)
  • RALP (right anterior/left posterior canals)
  • Overt and Covert saccades: compensatory eye movements detected during testing
    • Overt saccades (I remember overt because the head movement is OVERt)– compensatory eye movements following the completion of the head movement and observable with the naked eye (most associated with uncompensated peripheral impairment)
    • Covert saccades (I remember covert because the head movement COVERtS up the saccade)– compensatory eye movements during the head movement and unobservable with the naked eye (can be indicative of compensation status)
  • Most common measures evaluated are VOR gain and the presence of saccades
• Vestibular Evoked Myogenic Potential (VEMP): evaluation of the reflexive integrity of the otolith organs. VEMPs not only provide information on otolith function but can also aid in determining third window abnormalities, such as Semicircular Canal Dehiscence (SCD) by measuring the lowest stimulus level at which the reflex is evoked (reflex threshold).
  • Cervical VEMP (cVEMP) – a measure of the saccular and inferior vestibular nerve function. This ipsilateral response measures momentary decreases in the contraction of the Sternocleidomastoid (SCM) muscle through the vestibulocollic reflex by physical activation of the saccule via sound pressure (air or bone conduction)
  • Ocular VEMP (oVEMP) – a measure of the utricular and superior vestibular nerve function. This contralateral response measures momentary increases in contraction of the inferior oblique muscle by physical activation of the utricle via sound pressure

Other tests you may want to consider provides information regarding the patient’s overall function include:

• Computerized Dynamic Posturography (CDP):
  • Sensory Organization Test (SOT)
  • Motor Control Test (MCT)
  • Adaptation test (ADT)

Although this is not a comprehensive list of every possible vestibular test, we hope this general overview of the most common measures is of use to you in your clinical rotations. In our next post, we will discuss some common vestibular disorders and how a patient may present their symptoms to you.

Daniel J. Romero, AuD is currently working on his PhD degree with an emphasis in vestibular science at James Madison University. He obtained his Doctor of Audiology degree from Northern Illinois University in 2018. His interests include vestibular assessment and management, vestibular perception, and auditory and vestibular evoked potentials.

Liz Marler, BA is a fourth-year from Purdue University completing her externship at the Mayo Clinic in Phoenix, AZ. She is currently serving as the President of the SAA. Her interests include vestibular and electrophysiology.