Vestibular Testing Methods

Bedside Tests - Clinical Quick-Scans

• Dix-Hallpike Test: For PC-BPPV. Positive: torsional upbeating nystagmus (latent, fatigable).
• Roll Test (Supine): For HC-BPPV. Positive: horizontal nystagmus (geotropic/apogeotropic).
• Head Impulse Test (HIT): Assesses VOR. Part of HINTS.
  • Normal (no saccade): Central (stroke).
  • Abnormal (saccade): Peripheral (neuritis).
• HINTS Exam: 📌 (HI, Nystagmus, Test of Skew) for AVS (Stroke vs. Neuritis).
  • HI: Normal → Central.
  • Nystagmus: Direction-changing/Gaze-evoked/Vertical → Central.
  • TS (Test of Skew): Present → Central.

> ⭐ HINTS exam is more sensitive than early MRI (<**48h**) for stroke in AVS.

• Head Shaking Nystagmus (HSN): Unilateral vestibular loss. Head shake (20x); nystagmus beats to healthy side.
• Dynamic Visual Acuity (DVA): VOR function. Loss >2 lines (Snellen) with head motion (~2 Hz) = abnormal.

VNG/ENG - Labyrinthine Insights

• Principle: Records eye movements (nystagmus) to assess vestibular function. VNG (videonystagmography) uses cameras; ENG (electronystagmography) uses electrodes.
• Components:
  • Oculomotor Tests: Saccades, smooth pursuit, optokinetic nystagmus, gaze stability.
  • Positional Tests: Detect nystagmus in various head/body positions (e.g., Dix-Hallpike, Roll test recorded).
• Caloric Test:
  • Principle: Induces endolymphatic thermo-convection in horizontal SCC.
  • Procedure: Warm (44°C) & cool (30°C) water/air irrigation in each ear.
  • Interpretation: 📌 COWS mnemonic: Cold Opposite, Warm Same nystagmus.
  • Parameters:
    • Unilateral Weakness (UW): >20-25% indicates peripheral lesion. $UW = |((RC+RW) - (LC+LW)) / (RC+RW+LC+LW)| * 100%$ (Jongkees' formula).
    • Directional Preponderance (DP): >25-30% suggests peripheral or central lesion.
    • Fixation Suppression Index: Assesses central vestibular pathways.

⭐ The caloric test uniquely assesses each horizontal semicircular canal and its afferent pathways independently.

Rotation & Impulse - Angular VOR Tests

• Rotational Chair Test
  • Principle: Evaluates angular VOR across a range of physiological frequencies (typically 0.01-0.64 Hz).
  • Parameters: Gain, Phase, Asymmetry.
  • Indications: Suspected bilateral vestibular loss, inconclusive VNG, pediatric/difficult-to-test patients.
• Video Head Impulse Test (vHIT)
  • Principle: Objective quantification of Head Impulse Test (HIT) for high-frequency VOR.
  • Measures: VOR gain for each of 6 SCCs (normal VOR gain ~1.0; significant gain reduction <0.7-0.8), presence of overt/covert saccades.
  • Advantages: Quick, tests all SCCs, good for detecting peripheral vestibular deficits.

⭐ vHIT can detect isolated saccular or utricular damage by assessing individual semicircular canal function, which is not possible with caloric or rotational chair testing alone.

VEMPs & Posturography - Otolith & Overall Balance

• Vestibular Evoked Myogenic Potentials (VEMPs): Sound/vibration evoked muscle reflexes via otolith organs.
  • cVEMP (cervical): Tests saccule & inferior vestibular nerve. Recorded: Sternocleidomastoid (SCM). Key Params: P13-N23 latency, amplitude, threshold.
  • oVEMP (ocular): Tests utricle & superior vestibular nerve. Recorded: Contralateral inferior oblique. Key Params: N1-P1 latency, amplitude, threshold. 📌 SOUP: Superior-oVEMP-Utricle-Pathway.

  ⭐ In Superior Semicircular Canal Dehiscence (SSCD), cVEMP thresholds are characteristically ↓, and oVEMP amplitudes may be ↑ with air-conducted sound.

• Computerized Dynamic Posturography (CDP): Assesses overall balance by systematically disrupting visual, vestibular, & somatosensory inputs.
  • Sensory Organization Test (SOT): 6 conditions.
  • Utility: Quantifies functional balance, identifies malingering/aphysiologic patterns, monitors rehab.
  • Key Pattern: Vestibular dysfunction = instability/fall on SOT 5 & 6.

High‑Yield Points - ⚡ Biggest Takeaways

• Caloric test: COWS mnemonic for nystagmus; tests lateral SCC and identifies unilateral weakness.
• VNG/ENG: Records nystagmus; helps differentiate central vs. peripheral lesions.
• Dix-Hallpike maneuver: Diagnostic for BPPV; elicits characteristic torsional nystagmus.
• Head Impulse Test (HIT): Assesses VOR; overt saccade indicates peripheral hypofunction.
• cVEMP: Tests saccular function and inferior vestibular nerve.
• oVEMP: Tests utricular function and superior vestibular nerve.
• Rotary Chair Test: Evaluates bilateral vestibular loss or when calorics are equivocal.