Indications, Utility, and Interpretation of Vestibular Testing

Educational Objectives

The goal of this program is to improve the application of vestibular testing. After hearing and assimilating this program, the clinician will better be able to:

1. Recognize the limitations of vestibular testing in patients with dizziness.

2. Identify normal and abnormal outcomes for different vestibular tests.

3. List indications and contraindications for common
vestibular tests.

Summary

Challenges of vestibular testing (VT): providers often ask wrong question; normal results frequently reported as abnormal; tests difficult to interpret if clinician lacks familiarity with techniques and underlying physiology; time consuming, expensive, and uncomfortable for patients; appropriate application of results to improve management unclear

Usefulness of VT: VT does not identify cause of dizziness but rather whether weakness of peripheral vestibular system (VS) present; VT poorly correlated with dizziness; analysis of 24,000 patients shows VT not useful for diagnosing 2 most common causes of dizziness (benign paroxysmal positional vertigo and functional dizziness) and other disorders; VT potentially helpful in diagnosis of some central causes of dizziness and Ménière disease, and helpful for unilateral and bilateral vestibulopathy and superior canal dehiscence syndrome (SCDS); overall, VT useful in only ≈16% of patients with dizziness (subset of patients with suspicion of vestibular weakness); subjective measures of dizziness (eg, Dizziness Handicap Inventory) do not correlate with results of VT

Abnormal vs normal results: statistical problems arise because full battery of tests yields 50 different data points, most normal values based on small populations and 95% percent confidence intervals, and most tests do not have external gold standard (with exception of vestibular myogenic evoked potential [VEMP] tests compared with surgically-confirmed SCDS, and video head impulse tests [vHITs] compared with surgically confirmed lesions); tests should be interpreted as whole, not based on individual abnormal test values; outcome of VT often dependent on technique; understanding of tests aids in interpretation of results

Features of VT: VS consists of 5 end organs, 3 semicircular canals, utricle, and saccule; most tests assess single end organ (horizontal canal [HC]); videonystagmography (VNG), rotary chair testing (RCT), and vHIT all test HC, but use different frequencies of VS (VNG low frequency, RTC mid frequency, and vHIT high frequency), which helps to explain discordance between results of different tests in same patient; shows VS may have frequency-specific lesions

Physiology of VT: VS has baseline rate of firing that allows for increase and decrease in rate of firing and facilitates encoding of bidirectional information and more rapid transmission of information; when head turned to side, rate of firing increases on ipsilateral HC and decreases on contralateral HC, driving response of vestibular ocular reflex (VOR) to move eyes in equal and opposite direction to head turn; increasing unilateral rate of firing — most tests assess eye movements after stimulation of HCs; method of artificial stimulation uses temperature change produced with warm air or water in ear (caloric testing); whole-body rotations more natural stimulus, either back and forth (sinusoidal) or in circle (step velocity or trapezoid); in vHIT, examiner rapidly rotates only patient’s head (faster than RCT stimulus)

Videonystagmography: oculomotor testing — confirms normal oculomotor control; assesses saccades (rapid voluntary eye movements), smooth pursuit, and optokinetic nystagmus (smooth pursuit following moving visual field); nystagmus testing — patient wears infrared goggles to deny visual fixation and undergoes assessment for spontaneous, head shaking-induced, and positional nystagmus; caloric testing — uses air or water caloric systems; prerequisites — normal anatomy (presence of excess cerumen, perforation of tympanic membrane, or fluid in middle ear affects convection of temperature changes through eardrum to HC); other tests used preferentially in patients with abnormal anatomy or after surgery; results — as temperature changes over ≈90 sec, slow-phase eye velocity should increase, peak, then decrease at point when visual stimulus provided; normal tracings show typical sawtooth pattern, while more shallow slopes indicate vestibular weakness; interpretation — asymmetry calculated using Jongkees formula (absolute values of right side, minus left side, divided by total of all values); <25% considered normal, 25% to 35% borderline, and >35% abnormal (occurs with Ménière disease, severe neuritis, and vestibular neurectomy); criteria for absolute weakness — total eye speed <10° per ear or 20° overall (consistent with bilateral hypofunction)

Rotational chair testing: cannot determine laterality of lesion (not useful for unilateral vestibular loss); consists of sinusoidal rotations (back and forth at predetermined frequency; 4 frequencies tested) and step velocity (spin in circle at 100°/sec for prescribed amount of time); interpretation — for unilateral loss, sinusoidal rotation shows low-frequency phase lead (sidedness not indicated) and step velocity shows low time constants and decreased gain; for bilateral loss, sinusoidal rotation shows decreased gain across all frequencies (when severe, gain too low to allow computer to calculate phase or asymmetry)

Video head impulse testing: patient focuses on target while assessor performs quick impulse (200°/sec) in plane of semicircular canal tested; normal vHIT — gain of system ≈1 (ie, amount of eye movement equal and opposite to that of head turn); tracings of movement of left and right eyes mirror images; functionally, eyes remain on target; abnormal vHIT — tracings show eyes unable to stay on target, with catch-up saccades after head impulse; velocity regression shows gain of reflex 0.6; in patient with deficient VOR, low gain and catch-up saccades present; vHIT useful for identifying specific canal deficiencies

Vestibular evoked myogenic potentials: limitations — absence of response found in 10% to 15% of normal patients and increases exponentially with age (at >65 yr of age, VEMP unreliable and absence of response expected); response lost with any conductive hearing loss (VEMP measures response of muscle to sounds presented to ear); 2 types — cVEMP (cervical) measures inhibitory response of sternocleidomastoid muscle through saccule; oVEMP (ocular) measures inferior oblique muscle through utricle; VEMPs test otolith organs, not HC; cVEMP responses — relatively large and reproducible; characteristic upward deflection (P13) followed by downward deflection (N23); presence at low threshold consistent with SCDS (currently, single best test to diagnose SCDS); oVEMP responses — characteristic waveform at 10 ms and 20 ms; response >20 µV considered large

Clinical indications: VNG — central oculomotor disease; suspected unilateral or bilateral weakness; RCT — suspected bilateral weakness (single best indication; unable to detect unilateral weakness); vHIT — unilateral and bilateral weakness; tests all 3 canals (can identify selective impairment); VEMP — currently, only SCDS; potential use for identifying patterns with Ménière disease or isolated dysfunction of utricle and saccule (not considered clinical syndromes)

Contraindications: VNG — abnormal anatomy limits interpretation; RCT — claustrophobia; vHIT — blindness (unable to focus on target); cervical instability (unable to perform quick head thrust); VEMP — conductive hearing loss

Summary: VT only useful in subset of patients with dizziness (does not determine cause of dizziness); vHIT, VNG, and RCT can diagnose unilateral or bilateral vestibular loss but each tests different frequency (results do not correlate perfectly); if choosing single test, vHIT easiest to administer, highly sensitive and specific, least expensive, and most portable; VEMP superior test for diagnosing SCDS

Readings

Brandt T, Dieterich M: The dizzy patient: don’t forget disorders of the central vestibular system. Nat Rev Neurol 2017 Jun;13(6):352-362; Burston A et al: Comparison of the video head impulse test with the caloric test in patients with sub-acute and chronic vestibular disorders. J Clin Neurosci 2018 Jan;47:294-298; Chan FM et al: Normative data for rotational chair stratified by age. Laryngoscope 2016 Feb;126(2):460-3; Halmagyi GM et al: The video head impulse test. Front Neurol 2017 Jun 9;8:258; Heuberger M et al: Usability of the video head impulse test: lessons from the population-based prospective KORA study. Front Neurol 2018 Aug 17;9:659; Hunter JB et al: Cervical and ocular VEMP testing in diagnosing superior semicircular canal dehiscence. Otolaryngol Head Neck Surg 2017 May;156(5):917-923; Kumar L et al: Sensitivity and specificity of clinical and laboratory otolith function tests. Otol Neurotol 2017 Oct;38(9):e378-e383; McCaslin DL et al: Predictive properties of the video head impulse test: measures of caloric symmetry and self-report dizziness handicap. Ear Hear 2014 Sep-Oct;35(5):e185-91; Walther LE: Current diagnostic procedures for diagnosing vertigo and dizziness. GMS Curr Top Otorhinolaryngol Head Neck Surg. 2017 Dec 18;16:Doc02; Zuniga MG et al: Ocular versus cervical VEMPs in the diagnosis of superior semicircular canal dehiscence syndrome. Otol Neurotol 2013 Jan;34(1):121-6.

Disclosures

For this program, the following has been disclosed: Dr. Sharon reported nothing to disclose. The planning committees reported nothing to disclose. In his lecture, Dr. Sharon presents information related to the off-label or investigational use of a therapy, product, or device.

Acknowledgements

Dr. Sharon was recorded at the Pacific Rim Otolaryngology — Head and Neck Surgery Update, held February 18-19, 2018, in Honolulu, HI, and presented by the University of California, San Francisco, School of Medicine. For information on future CME activities from this sponsor, please visit www.meded.ucsf.edu/cme. The Audio Digest Foundation thanks the speakers and sponsors for their cooperation in the presentation of this program.

CME/CE INFO

Accreditation:

The Audio- Digest Foundation is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The Audio- Digest Foundation designates this enduring material for a maximum of 0 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Audio Digest Foundation is accredited as a provider of continuing nursing education by the American Nurses Credentialing Center's (ANCC's) Commission on Accreditation. Audio Digest Foundation designates this activity for 0 CE contact hours.

Lecture ID:

OT512302

Expiration:

This CME course qualifies for AMA PRA Category 1 Credits™ for 3 years from the date of publication.

Instructions:

To earn CME/CE credit for this course, you must complete all the following components in the order recommended: (1) Review introductory course content, including Educational Objectives and Faculty/Planner Disclosures; (2) Listen to the audio program and review accompanying learning materials; (3) Complete posttest (only after completing Step 2) and earn a passing score of at least 80%. Taking the course Pretest and completing the Evaluation Survey are strongly recommended (but not mandatory) components of completing this CME/CE course.

Estimated time to complete this CME/CE course:

Approximately 2x the length of the recorded lecture to account for time spent studying accompanying learning materials and completing tests.