Head impulse test

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Head impulse test with a defective left labyrinth. The normal patient maintains fixation throughout. The patient with a defective left labyrinth loses fixation with the rapid head movement and must make a catch-up saccade to the right.
The head impulse test (HIT), or head thrust test, is used to help identify an impaired vestibulo-ocular reflex (VOR) in patients with vertigo, particularly in suspected acute peripheral vestibulopathy.(1-4) The examiner briskly rotates the patient’s head while having the patient fixate on a target, usually the examiner’s nose. During slow head movements the ocular smooth pursuit system normally maintains fixation. Rapid head movements exceed the capability of smooth pursuit and the VOR then must maintain fixation. When the VOR is impaired, ocular tracking fails during the rapid head movement requiring a “catch-up”saccade to reacquire the target at the end of the movement.

To perform the test, instruct the patient to maintain fixation on the examiner’s nose, then rotate the patient’s head slowly to each side, then briskly back to midline, or from midline to each side. Normally, the VOR is able to match the velocity of head rotation and fixation never leaves the nose. With a vestibulopathy on the side to which the head is quickly rotated, the impaired VOR causes the eyes to lag behind during the rapid head movement, fixation is lost and a corrective saccade back to the target occurs. The catch up saccade indicates peripheral vestibular hypofunction on the side towards which the head was rotated (Figure). The video is of a patient with acute left vestibular neuritis. The head impulse is positive toward the left.

The HIT is useful in evaluating patients with acute spontaneous vertigo since it is positive, revealing a catch-up saccade, in acute peripheral vestibulopathy but usually, although not invariably, negative with central vestibular lesions. For the diagnosis of peripheral vestibular disease, defined by an abnormal caloric response, the presence of a corrective saccade on the head impulse test has a sensitivity of 35-57%, a specificity of 90-99%, a positive LR of 6.7 and a negative LR of 0.6.5 A reliable three-step bedside examination to distinguish brainstem stroke from acute peripheral vestibulopathy is the HINTS – head impulse, nystagmus, test of skew.(5)

In a patient with left vestibulopathy, the defective VOR comes out with the quick movement to the left. If the head is moved from neutral to left the saccade would be to the right; if moved from right to neutral the saccade would also be to the right because the patient starts in horizontal conjugate gaze to the left and with the quick leftward movement the eyes remain in left gaze instead of moving to the right, requiring a corrective saccade to the right at the end of the head movement.

The corrective saccade is always in the plane of the specific semicircular canal activated and away from the defective canal.

The video by Bassani demonstrates another example of an an abnormal head impulse test in a patient with a peripheral vestibulopathy with a very obvious catch-up saccade, as well as an abnormal Unterberger-Fukuda stepping test.(6) In this video the corrective saccade is very obvious. The video depicts spontaneous right-beating nystagmus with vertical and counter-clockwise components. The nystagmus increases with gaze shift toward the pathological left side and decreases with gazing toward the right side. On the HIT, the quick rotation of the patient’s head toward the pathological left side causes an eye lag, followed by a catch-up saccade to re-fixate on the target. The last part of the video shows a 45° rotation toward the pathological left side during the stepping test.

Video courtesy of Dr. Jorge Kattah of the University of Illinois Peoria campus

References

1. Campbell WW. DeJong's the neurologic examination, 7th ed. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2013. 2. Campbell WW. Clinical signs in neurology : a compendium. Philadelphia: Wolters Kluwer Health, 2016. 3. Alhabib SF, Saliba I. Video head impulse test: a review of the literature. Eur Arch Otorhinolaryngol. 2017 Mar;274(3):1215-1222. 4. Weber KP, MacDougall HG, Halmagyi GM, Curthoys IS. Impulsive testing of semicircular-canal function using video-oculography. Ann N Y Acad Sci. 2009 May;1164:486-91. 5. Kattah JC, Talkad AV, Wang DZ, Hsieh YH, Newman-Toker DE. HINTS to diagnose stroke in the acute vestibular syndrome: three-step bedside oculomotor examination more sensitive than early MRI diffusion-weighted imaging. Stroke. 2009 Nov;40(11):3504-10. 6. Bassani R. Teaching Video NeuroImages: vestibular neuritis: basic elements for clinical and instrumental diagnosis. Neurology. 2011 Apr 5;76(14):e71.