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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 (link to neurosigns) ]] – 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.