How Can Clinicians Use Advanced vHIT Interpretation to Improve Diagnosis and Patient Management?

Question

Answer

INTRODUCTION

The Video Head Impulse Test (vHIT) has firmly established itself as a cornerstone of vestibular diagnostics. While its role in identifying unilateral vestibular loss and differentiating central from peripheral causes is now well-recognized, the true clinical strength of vHIT lies in how we interpret subtle patterns beyond simple gain values.

This article focuses on advanced interpretation parameters and specialized clinical applications, aiming to refine how audiologists, ENTs, neurologists, and physiotherapists integrate vHIT into practice.

BEYOND GAIN: ADVANCED REPORTING PARAMETERS

1. High-velocity impulses

• Horizontal canals require ≥150°/s, vertical ≥100°/s to ensure vestibular rather than visual tracking is tested.
• Decline in gain at very high velocities (≥220°/s) often unmasks subtle hypofunction.

2. Covert and overt saccades

• Covert saccades: diagnostic even if gain is normal, signaling compensated vestibular loss.
• Overt saccades: strongly associated with acute deficits, latency ~ 200 ms post-impulse.

3. Dispersion analysis

• Horizontal dispersion: wide scatter of saccades across impulses signals incomplete or unstable compensation.
• Vertical dispersion: variability in eye traces, often seen in central compensation or during recovery.

4. Anti-compensatory quick eye movements (AQEM)

• Eye movements in the same direction as head thrust, opposite of expected compensation.
• Observed in Ménière’s disease and vestibular migraine; rarely in central lesions.
• Covert AQEM may indicate subtle asymmetry, overt AQEM peripheral hypofunction.

5. Artifacts

• Blinks, corneal reflex dropout, poor fixation, and goggle slippage can all mimic pathology.
• Clues: sudden gain drop without saccades, noisy traces, or “eye faster than head” appearances.

PERIPHERAL VESTIBULAR DISORDERS: ADVANCED APPLICATIONS

1. Acute Unilateral Vestibulopathy (AUVP)

vHIT not only confirms peripheral loss but also maps canal-specific deficits, e.g., isolated lateral/anterior involvement vs total loss. Recovery can be tracked as scattered saccades evolve into gathered, more efficient corrective movements.

2. Ménière’s Disease

Stage-dependent findings are critical:

• During an attack: transient canal deficits.
• Between attacks: possible normalization.
• Late disease: progressive, multi-canal hypofunction.
• After intratympanic gentamicin: confirmation of vestibular ablation.

3. Benign Paroxysmal Positional Vertigo (BPPV)

vHIT is usually normal, but helps in:

• Persistent/atypical BPPV (identifying associated paresis).
• Post-maneuver checks (detecting transient canalith jam).
• Differentiating central positional vertigo (normal vHIT) from complex BPPV (abnormal vHIT).

4. Bilateral Vestibulopathy

• Gain reduction across all canals without asymmetry.
• Velocity-dependent worsening, an important marker for true bilateral hypofunction.
• Rehabilitation planning based on spared canal function.

5. Presbyvestibulopathy

• vHIT gain 0.6–0.83 bilaterally in patients > 60 years.
• Explains imbalance, falls, and gait disturbances.
• A distinct entity with public health importance in fall prevention.

6. Ototoxic and Post-Surgical Disorders

• Gentamicin: detects bilateral high-frequency loss early.
• Post-cochlear implantation: reveals iatrogenic posterior canal injury.
• Post-labyrinthectomy or nerve section: tracks recovery and compensation.

CENTRAL AND SPECIALIZED DISORDERS

1. Wernicke’s Encephalopathy

Selective bilateral horizontal canal dysfunction with spared vertical canals, reflecting medial vestibular nucleus involvement.

2. CANVAS Syndrome

• Bilateral VOR loss across all canals, often preceding cerebellar signs.
• Serial vHIT demonstrates progressive decline, supporting early diagnosis.

3. Internuclear Ophthalmoplegia & Strokes

• Disconjugate VOR or selective canal abnormalities can localize brainstem lesions.
• Normal vHIT in severe vertigo may suggest cortical/cerebellar pathology.

4. Vestibular Migraine

Occasionally elevated VOR gain with AQEM, pointing to altered central processing.

PRACTICAL PEARLS FOR CLINICIANS

1. Always correlate abnormal vHIT with calorics and VEMPs, each tests different frequency ranges.
2. Repeat testing when dispersion or artifacts obscure interpretation.
3. Use vHIT longitudinally: rehabilitation progress is often visible as covert saccades emerge and become more consistent.
4. Be cautious in patients with ocular misalignment post-surgery; results may be unreliable.

INTEGRATION INTO CLINICAL PATHWAYS

The greatest strength of vHIT lies in triangulation with other tests:

• Calorics (low frequency, ~0.003 Hz).
• Rotatory chair (mid-frequency, ~0.1–0.5 Hz).
• vHIT (high frequency, 3–7 Hz).
• VEMPs (very high frequency, >100 Hz).

This frequency-specific framework allows clinicians to detect subtle, spectrum-based dysfunction, e.g., early Ménière’s with abnormal calorics but normal vHIT vs vestibular neuritis with the opposite pattern.

KEY TAKEAWAYS

• vHIT interpretation goes beyond gain values: dispersion, saccade morphology, AQEM, and artifacts provide vital diagnostic information.
• It is indispensable in stage-dependent evaluation of Ménière’s disease, atypical BPPV, and monitoring after gentamicin or surgery.
• Presbyvestibulopathy and bilateral vestibulopathy highlight its role in fall prevention and chronic imbalance.
• Central disorders such as Wernicke’s encephalopathy and CANVAS show unique vHIT patterns.
• A comprehensive vestibular workup requires combining vHIT with calorics, VEMPs, and clinical history.

References

• Newman-Toker DE, et al. Diagnostic approach to acute vestibular syndrome. Stroke. 2013.
• Casani AP, Navari E. Lesion patterns in acute unilateral vestibulopathy. Otol Neurotol. 2020.
• Yacovino DA. vHIT in Ménière’s disease.
• Strupp M, et al. Bilateral vestibulopathy: diagnostic criteria consensus. J Vestib Res. 2017.
• SAGE IJVR criteria for presbyvestibulopathy, 2019.

Resources for More Information 

• Discover our solutions for vestibular analysis on our website:

https://www.inventis.it/en-na/solutions/balance-unique-solutions

• Check out the following courses published on AudiologyOnline:

• Fundamentals of Video Head Impulse Test: Lesson 1 – Principles and Mechanics
• Fundamentals of Video Head Impulse Test: Lesson 2 – Clinical Applications and Interpretation
• Fundamentals of Video Head Impulse Test – Lesson 3: Clinical Applications and Case Studies