Head Impulse Test

The Head Impulse Test (HIT), also known as the Head Thrust Test, was first described in 1988 by Michael Halmagyi and Ian Curthoys as a rapid and reliable bedside tool to identify unilateral peripheral vestibular hypofunction¹. It is especially valuable in cases of acute vertigo, helping clinicians distinguish between central and peripheral causes.

HIT evaluates the function of the vestibulo-ocular reflex (VOR) – the brainstem-mediated reflex that stabilizes vision during rapid head movements. When the head rotates quickly, the eyes should move equally fast in the opposite direction to maintain fixation on a target. Failure of this reflex results in catch-up eye movements, a hallmark of vestibular dysfunction.

Physiological Background – Vestibulo-Ocular Reflex (VOR)

The VOR is triggered by the semicircular canals in the inner ear. When the head accelerates, hair cells in the canals detect the motion and send signals through the vestibular nerve to the brainstem. These signals are relayed to the ocular motor nuclei, generating rapid compensatory eye movements.

• Normal function: eyes remain fixed on the target without correction.

• Vestibular failure: the eyes move with the head, followed by a corrective saccade (fast eye movement) back to the target.

This is typically seen in vestibular neuritis, labyrinthine injury, or after vestibular loss.

Advantages of the Test

• Quick and simple to perform

• Useful in acute vertigo without advanced equipment

• Clear results in cases of severe unilateral vestibular loss

• Can be repeated safely with minimal discomfort

Test Procedure

Starting position:

• Patient sits opposite the examiner.

• Patient fixates on the examiner’s nose or a stationary point on the wall.

• Head is flexed forward by ~30° to align semicircular canals horizontally.

Execution:

1. Ensure no contraindications (neck pain, reduced cervical ROM, vertebrobasilar insufficiency).

2. Instruct the patient to maintain visual fixation.

3. Examiner holds the patient’s head firmly with both hands.

4. Apply a small, rapid, and unpredictable head thrust (10–15°) to the right or left.

5. Observe the eyes:

   • Normal: eyes stay on the target.

   • Abnormal: eyes move with the head, then correct back to the target with a saccade.

Interpretation

• Positive HIT (abnormal VOR): corrective saccade present → suggests peripheral vestibular dysfunction on the side to which the head was moved.

• Negative HIT (normal VOR): eyes remain fixed → suggests intact vestibular function.

Example: A positive test when turning to the right indicates right-sided vestibular hypofunction.

Sensitivity and Specificity

• Specificity: High (82–100 %)² → excellent for confirming vestibular loss.

• Sensitivity: Low to moderate (34–39 %)³ → may miss partial or bilateral dysfunction.

• Improved sensitivity: Forward flexion (~30°) increases detection to 71–84 %⁴.

• Threshold: Dysfunction often goes undetected unless >50 % of canal function is lost⁵.

Limitations and Pitfalls

• Most reliable in acute, complete unilateral loss.

• Less accurate in bilateral or partial hypofunction.

• May be falsely negative in central vertigo (e.g., cerebellar infarction).

• Covert saccades (hidden corrective eye movements) may require video Head Impulse Test (vHIT) for detection.

Clinical Use

HIT is most valuable as part of the HINTS exam (Head Impulse, Nystagmus, Test of Skew) for acute vertigo:

• Positive HIT + peripheral nystagmus + no skew deviation → peripheral cause.

• Negative HIT with central features → possible stroke → urgent imaging.

It can also be combined with:

• Caloric testing

• Video HIT (vHIT)

• Rotational chair testing

for more detailed vestibular evaluation.

Summary

The Head Impulse Test is a fast, non-invasive, and highly specific clinical tool for assessing vestibular function. It plays a key role in differentiating central from peripheral causes of vertigo in emergency and outpatient settings. While a positive HIT strongly supports peripheral vestibular dysfunction, its limited sensitivity means it should be used in combination with other diagnostic tests and patient history.

Sources:

1. Halmagyi GM, Curthoys IS. A clinical sign of canal paresis. Archives of Neurology. 1988;45:737–739.

2. Kuo CH, Pang L, Chang R. Vertigo – part 1 – assessment in general practice. Australian Family Physician. 2008;37(5):341–347.

3. Curthoys IS, Manzari L. Clinical application of the head impulse test of semicircular canal function. Hearing, Balance and Communication. 2017;15(3):113–126. DOI: 10.1080/21695717.2017.1353774

4. Halmagyi GM, Cremer PD. Assessment and treatment of dizziness. Journal of Neurology, Neurosurgery & Psychiatry. 2000;68:129.

5. MacDougall HG, Weber KP, McGarvie LA, et al. The video head impulse test: diagnostic accuracy in peripheral vestibulopathy. Neurology. 2009;73:1134.

6. Harvey SA, Wood DJ, Feroah TR. Relationship of the head impulse test and head-shake nystagmus in reference to caloric testing. American Journal of Otology. 1997;18:207.

7. Harvey SA, Wood DJ. The oculocephalic response in the evaluation of the dizzy patient. Laryngoscope. 1996;106:6.

8. Beynon GJ, Jani P, Baguley DM. A clinical evaluation of head impulse testing. Clinical Otolaryngology and Allied Sciences. 1998;23(2):117–122.

9. Schubert MC, Tusa RJ, Grine LE, Herdman SJ. Optimizing the sensitivity of the head thrust test for identifying vestibular hypofunction. Physical Therapy. 2004;84:151.

10. Hamid M. More than a 50% canal paresis is needed for the head impulse test to be positive. Otology & Neurotology. 2005;26(2):318–319.