Abnormal Active Head Impulse Testing Recorded Asynchronously in Bilateral Vestibular Loss

This is a video of patient with the subacute onset of head movement-dependent oscillopsia due to bilateral vestibular loss (with obvious bilaterally abnormal head impulse test (HIT) at the bedside), in addition to central ocular motor signs including saccadic smooth pursuit and gaze-evoked nystagmus. Given bilateral vestibular loss and impaired pursuit, the visually-enhanced vestibulo-ocular reflex (vVOR) was also saccadic (for additional details on this patient's history and exam, go to https://collections.lib.utah.edu/ark:/87278/s6xt1440). The patient was asked to make a video of himself performing the head impulse test to the right and left. While at the bedside and with video HIT, the right VOR (in the planes of horizontal, anterior and posterior canals) was more impaired, interestingly, abnormal HITs to the left are apparent in this video, while HITs appear normal to the right side. Perhaps this relates to the fact that he could generate higher velocity HITs to the left compared to the right, or had to do with the amplitude of the left-sided HITs or other factors. There were likely corrective saccades occurring during head movements to the right, and these ‘covert' saccades gave the appearance of a normal HIT to the right. It has been shown that the active HIT is much more likely to result in false negatives compared to passive (performed by the examiner) HITs, even in patients who were trained to perform the maneuver correctly.(1) This is mainly due to the fact that the corrective saccades generated in a patient with unilateral or bilateral vestibular loss occur during the head movement with active HITs as opposed to after the head movement with passive HITs (i.e., an earlier corrective saccade with active HIT). In the same study, it was also shown that gains (ratio of the output (eye movement) to input (head movement)) as measured by vHIT were higher with active HITs.(1) For these reasons, evaluating the VOR with active HIT alone is inadequate to detect vestibular loss at the bedside - or via telemedicine - in the vast majority of patients.Black RA, Halmagyi GM, Thurtell MJ, Todd MJ, Curthoys IS. The active head-impulse test in unilateral peripheral vestibulopathy. Arch Neurol. 2005;62(2):290-3