Vestibular Testing

Vestibular System & Bedside Tests - Dizzy Doctor's Drill

Key to balance: Vestibular labyrinth (SCCs, otoliths) detects head motion; VOR stabilizes gaze.

Cardinal Symptoms:

• Vertigo: Sensation of spinning/dizziness.
• Nystagmus: Involuntary rhythmic eye movements.
• Ataxia: Gait imbalance, unsteadiness.

Bedside Clinical Tests:

📌 HINTS exam (for acute vestibular syndrome): Head Impulse, Nystagmus type, Test of Skew deviation - helps differentiate stroke from peripheral vestibulopathy (e.g., vestibular neuritis).

VNG/ENG Tests - Eyeing the Imbalance

Videonystagmography (VNG) / Electronystagmography (ENG) objectively assess vestibular and oculomotor function.

• Oculomotor Tests: Evaluate central neural pathways.

  • Saccades: Rapid eye movements to track a target.
  • Smooth Pursuit: Following a slowly moving target.
  • Optokinetic Nystagmus (OKN): Nystagmus induced by moving visual field.
  • Gaze Stability: Maintaining gaze without nystagmus.

  Test	Key Abnormality	Likely Site
  Saccades	Inaccuracy, Slowing	Central
  Smooth Pursuit	Low Gain, Jerky	Central
  Optokinetic	Asymmetry	Central
  Gaze Stability	Gaze-evoked Nystagmus	Central/Peripheral

• Positional Testing: Detects Benign Paroxysmal Positional Vertigo (BPPV).

  • Dix-Hallpike Test: For posterior canal BPPV.
  • Supine Roll Test: For horizontal canal BPPV.

• Caloric Testing: Assesses horizontal semicircular canal function individually.

  • Principle: Thermal stimulation (warm/cold water or air) of ear canal induces endolymphatic flow, causing nystagmus.
  • 📌 COWS: Cold water, Opposite beating nystagmus (fast phase); Warm water, Same side beating nystagmus.
  • Canal Paresis (CP): $CP = \frac{(RC+RW)-(LC+LW)}{(RC+RW+LC+LW)} \times 100%$. Significant if $> extbf{25}%$.
  • Directional Preponderance (DP): $DP = \frac{(RW+LC)-(RC+LW)}{(RC+RW+LC+LW)} \times 100%$. Significant if $> extbf{30}%$.

  

⭐ Bithermal caloric testing is the cornerstone for identifying side-specific peripheral vestibular weakness.

Advanced Vestibular Tests - Probing Deeper

• Rotational Chair Test:
  • Broad-frequency VOR check.
  • For: Bilateral vestibular loss.
  • Finds: ↓ Gain, phase lead, asymmetry.
• cVEMP (Cervical Vestibular Evoked Myogenic Potential):
  • Tests saccule & inf. vestibular nerve (sound/vib → SCM response).
  • Finds: ↓ Amplitude, ↑ threshold, asymmetry > extbf{35-40}%.
• oVEMP (Ocular Vestibular Evoked Myogenic Potential):
  • Tests utricle & sup. vestibular nerve (sound/vib → EOM response).
  • Finds: ↓ Amplitude, ↑ threshold, asymmetry > extbf{35-40}%.
  • VEMP Asymmetry Ratio: $AR = \frac{(Amp_{larger} - Amp_{smaller})}{(Amp_{larger} + Amp_{smaller})} \times 100%$
• vHIT (Video Head Impulse Test):
  • Assesses indiv. SCC VOR (rapid head turns).
  • For: Peripheral hypofunction.
  • Finds: ↓ VOR gain < extbf{0.7-0.8}, corrective saccades.

⭐ cVEMP assesses saccular and inferior vestibular nerve function, while oVEMP assesses utricular and superior vestibular nerve function.

High‑Yield Points - ⚡ Biggest Takeaways

• VNG/ENG differentiates central vs. peripheral vestibular lesions; caloric testing (COWS) is a cornerstone.
• Dix-Hallpike maneuver is diagnostic for BPPV; Epley maneuver treats posterior canal BPPV.
• cVEMP assesses saccule & inferior vestibular nerve; oVEMP for utricle & superior vestibular nerve.
• Head Impulse Test (HIT) showing corrective saccades indicates peripheral VOR deficit.
• Gaze-evoked nystagmus, especially direction-changing, points to central pathology.
• Fistula test (Hennebert's sign) suggests perilymphatic fistula or superior canal dehiscence_._