How is the bedside head‑impulse test performed and interpreted to differentiate peripheral vestibular lesions from central causes of acute vertigo?

Head Impulse Test: Performance and Interpretation

How to Perform the Bedside Head Impulse Test

The head impulse test (HIT) is performed by applying a rapid, unpredictable, small-amplitude (10–20°) head rotation while the patient fixates on a target, looking for corrective catch-up saccades that indicate peripheral vestibular dysfunction. 1

Step-by-Step Technique

• Position the patient seated, facing you at arm's length, with their gaze fixed on your nose or a central target 2
• Grasp the patient's head firmly with both hands on either side 2
• Instruct the patient to keep their eyes locked on the target throughout the maneuver 2
• Apply a rapid, unpredictable head rotation of 10–20° to one side, reaching peak velocity of 150–250°/second 2, 3
• Observe the patient's eyes during and immediately after the head movement 2
• Repeat 10–20 times in each direction (right and left), varying the timing to prevent anticipation 3
• The test must be performed with sufficient velocity and unpredictability; slow or predictable movements invalidate the results 2

Interpretation: Peripheral vs. Central Patterns

Normal (Central) Pattern

A normal head impulse test—where the eyes remain fixed on target without corrective saccades—strongly suggests a central cause of vertigo, particularly posterior circulation stroke, and mandates urgent neuroimaging. 1, 4

• Eyes remain locked on the target throughout and after the head rotation 4
• No corrective saccades are visible 4
• The vestibulo-ocular reflex (VOR) is intact bilaterally 4
• In acute vestibular syndrome, a normal HIT has 91% specificity for stroke 4
• Critical point: Normal HITs in a patient with acute continuous vertigo, nystagmus, and gait instability should prompt immediate MRI, as this pattern indicates central pathology in 91% of cases 4

Abnormal (Peripheral) Pattern

An abnormal head impulse test—characterized by visible corrective catch-up saccades—indicates peripheral vestibular hypofunction (vestibular neuritis or labyrinthitis) in the vast majority of cases. 1, 4

• Overt saccades: Eyes move off target with the head, then a visible corrective saccade brings them back to the target after the head stops moving 2, 3
• Covert saccades: Corrective saccades occur during the head rotation and may not be visible to the naked eye, requiring video-oculography for detection 2, 3
• The abnormal side is the side toward which the head is rotated when the corrective saccade appears 3
• In acute vestibular syndrome, a positive HIT has 100% sensitivity for peripheral vestibulopathy 4

Critical Diagnostic Pitfalls

The 9% Exception: Positive HIT Does Not Guarantee Benign Disease

Approximately 9% of cerebellar and lateral pontine strokes can produce an abnormal (positive) head impulse test, mimicking peripheral vestibular neuritis. 4

• Vestibulocerebellar, pontocerebellar, and pontocerebello-labyrinthine strokes can all show positive HITs 4
• Lesions involving the vestibular nucleus, nucleus prepositus hypoglossi, or flocculus may produce unilateral or bilateral VOR gain reduction 5
• Therefore, a positive HIT alone cannot exclude stroke; additional examination findings must be assessed 4

Distinguishing Features When HIT is Positive

When the HIT is abnormal, evaluate these additional features to differentiate stroke from vestibular neuritis:

• Direction-changing nystagmus (beats right in right gaze, left in left gaze) indicates central pathology 6, 1
• Pure vertical nystagmus without torsional component suggests stroke 6, 1
• Severe truncal instability with inability to sit or stand unsupported points to cerebellar stroke 1, 4
• Skew deviation on alternate cover test indicates brainstem involvement 1, 7
• Sudden unilateral hearing loss with vertigo suggests labyrinthitis (peripheral) or AICA stroke (central) 7, 8

Bedside HIT Limitations

• Covert saccades are missed in 30–40% of cases by bedside examination alone, leading to false-negative results 2, 3
• Video head impulse testing (vHIT) detects both overt and covert saccades with 100% sensitivity and specificity 3, 9
• A simple automated vHIT algorithm using VOR gain cutoff of 0.7 correctly identifies 100% of normal/central patterns 9

Integration into the HINTS Examination

The head impulse test is the "H" in the HINTS battery (Head Impulse, Nystagmus, Test of Skew), which has 96.7% sensitivity and 94.8% specificity for stroke when performed by trained specialists. 7

HINTS Interpretation Algorithm

• Any ONE central finding mandates urgent MRI: 7
  • Normal head impulse test (intact VOR)
  • Direction-changing or pure vertical nystagmus
  • Skew deviation present
• All THREE peripheral findings suggest vestibular neuritis: 7
  • Abnormal head impulse test (corrective saccades)
  • Unidirectional horizontal-torsional nystagmus
  • No skew deviation

HINTS Performance Caveat

HINTS achieves high accuracy only when performed by trained neuro-otology specialists; emergency physicians without specialized training should not rely on HINTS alone to exclude stroke. 7

• Subspecialists achieve 97.6% specificity vs. 89.1% for non-subspecialists 7
• Meta-analyses show inadequate sensitivity when emergency physicians perform HINTS in isolation 7
• Recommendation: In high-risk patients (age >50, vascular risk factors), obtain MRI regardless of HINTS results 7, 8

When to Image Despite Test Results

Proceed directly to MRI brain with diffusion-weighted imaging if any of these features are present, regardless of HIT findings: 1, 8

• Age >50 years with hypertension, diabetes, atrial fibrillation, or prior stroke
• New severe headache accompanying vertigo
• Any focal neurologic deficit (dysarthria, limb weakness, diplopia, dysphagia)
• Inability to stand or walk without assistance
• Downbeating nystagmus on Dix-Hallpike maneuver
• Baseline nystagmus present without provocative maneuvers