What is the role of the head impulse test (HIT) in diagnosing and managing vestibular dysfunction?

Head Impulse Test in Vestibular Dysfunction

The head impulse test (HIT) is a bedside clinical examination that assesses the vestibulo-ocular reflex (VOR) by detecting corrective saccades during rapid head rotations, primarily used to differentiate peripheral vestibular lesions (abnormal test) from central causes like stroke (normal test) in patients with acute vestibular syndrome. 1, 2

Core Diagnostic Principle

The HIT evaluates the integrity of individual semicircular canals by testing the VOR during high-velocity head rotations 3, 4. The fundamental diagnostic distinction is:

• Abnormal HIT (corrective saccades present) = Peripheral vestibular dysfunction (e.g., vestibular neuritis) 5
• Normal HIT = Suggests central pathology (e.g., stroke) in patients with acute vestibular syndrome 6, 4

This makes the HIT particularly valuable in the emergency setting for identifying stroke risk in dizzy patients 6.

Clinical vs. Video-Based HIT

Bedside Clinical HIT

• Established as a standard bedside examination for detecting peripheral vestibular impairment 3
• Critical limitation: Clinicians may miss subtle corrective saccades, particularly covert saccades that occur during the head movement rather than after 5
• This can lead to false-negative results where peripheral deficits are missed 5

Video Head Impulse Test (vHIT)

• Quantifies VOR function with high accuracy (250 Hz recording) and detects both overt and covert corrective saccades that are imperceptible during bedside examination 5
• Diagnostic accuracy: Sensitivity and specificity of 1.0 (100%) for detecting peripheral vestibular deficits when compared to the gold standard search coil technique 5
• Easy to use, well-tolerated by patients, and applicable even in acute vestibular neuritis 7, 5
• Simple interpretation algorithm: VOR gain cutoff of 0.7 provides 100% specificity for detecting normal/central VOR (ruling out stroke) with 75.6% sensitivity for abnormal/peripheral findings 6

When to Order HIT/vHIT Testing

Appropriate Indications

The American Academy of Otolaryngology-Head and Neck Surgery recommends vHIT when 1, 2:

• Diagnosis of vertigo/dizziness remains unclear after clinical assessment
• Clinical presentation is atypical for common vestibular disorders
• Positional testing elicits equivocal or unusual nystagmus patterns
• Additional symptoms suggest accompanying CNS or otologic disorders
• Multiple concurrent peripheral vestibular disorders are suspected
• Patients remain symptomatic following treatment

When NOT to Order

Do not routinely order vHIT for clear clinical diagnoses such as 1, 2:

• Benign Paroxysmal Positional Vertigo (BPPV) when diagnostic criteria are met
• Ménière's disease with typical history and symptoms
• Vestibular neuritis with classic presentation (unless atypical features present)

Unnecessary testing leads to delays in diagnosis, increased costs, and patient discomfort without changing management 1, 2.

Advanced Pattern Recognition in Central Lesions

While normal HITs typically indicate central pathology, specific abnormal HIT patterns can also indicate central vestibular disorders 4:

Central Lesion Patterns

• Vestibular nucleus/nucleus prepositus hypoglossi/flocculus lesions: Unilaterally or bilaterally reduced horizontal VOR gains (positive HITs) 4
• Diffuse cerebellar lesions: Hyperactive (increased) VOR gain with corrective saccades directed opposite to the expected direction 4
• Cross-coupled vertical corrective saccades during horizontal HITs suggest diffuse cerebellar pathology 4
• Medial longitudinal fasciculus lesions: Abnormal vertical HIT gains 4

Clinical Implication

Discrepancies between clinical bedside HIT and quantitative vHIT can occur, making video-based testing superior for detecting subtle central patterns that might be missed clinically 4.

Integration into Clinical Algorithm

Step 1: Clinical Assessment

Determine if presentation suggests peripheral vs. central pathology based on onset, duration, associated symptoms, and neurological examination 1, 2.

Step 2: Bedside HIT

Perform clinical HIT as initial screening, recognizing its limitations for detecting covert saccades 3, 5.

Step 3: vHIT Indications

Order vHIT when 1, 2, 7:

• Bedside HIT is equivocal or contradicts clinical suspicion
• High-risk features for stroke are present (e.g., vascular risk factors, additional neurological signs)
• Diagnosis remains unclear despite clinical evaluation
• Quantitative documentation is needed for treatment planning or monitoring

Step 4: Interpretation

• VOR gain <0.7: Peripheral vestibular deficit 6
• VOR gain ≥0.7: Normal VOR, consider central pathology in acute vestibular syndrome 6
• Abnormal patterns with normal gain: Consider central lesions (cerebellar, brainstem) 4

Common Pitfalls

• Assuming normal bedside HIT rules out peripheral pathology: Covert saccades may be missed clinically but detected on vHIT 5
• Over-reliance on testing for clear diagnoses: Normal vHIT results do not rule out vestibular disorders like Ménière's disease, as test results fluctuate and correlate poorly with patient-perceived disability 1, 2
• Ignoring central patterns: Abnormal HITs can occur with central lesions, not just peripheral pathology 4
• Artifact misinterpretation: Approximately 3% of vHITs may be uninterpretable due to technical artifacts 6

Impact on Clinical Outcomes

The vHIT has potential to improve detection of vestibular dysfunction across multiple neurological conditions (polyneuropathy, cerebellar ataxia) beyond traditional vestibular diseases, providing quantitative measures for longitudinal assessment of therapeutic interventions 7. In the emergency setting, the ability to reliably detect normal VOR (100% specificity) makes vHIT a valuable stroke screening tool for patients presenting with acute vestibular syndrome 6.