Test Your Knowledge: The Acute Vestibular Syndrome with Gaze-Evoked Nystagmus and Bilaterally Abnormal Head Impulse Testing Due to Middle Cerebellar Peduncle and Flocculus Hemorrhage

This is a 70-year-old woman with a history of atrial fibrillation on warfarin presenting with acute prolonged vertigo and imbalance. In addition to the findings demonstrated in the first part of the video, what else should be seen to reassure the examiner that the etiology of her vertigo is benign? A. Right beating nystagmus in left gaze, a right hypertropia with alternate cover testing, abnormal head impulse test (HIT) to the left, and normal hearing. B. Left beating nystagmus in left gaze, a right hypertropia increasing in left and downgaze and in right head tilt with alternate cover testing, normal HIT to the left, and normal hearing. C. Left-beating nystagmus in left gaze, no vertical heterophoria/heterotropia, abnormal HIT to the left, and decreased hearing on the left. D. Right-beating nystagmus in left gaze, no vertical heterophoria/heterotropia, abnormal HIT to the left and normal hearing. A. Incorrect. The Head Impulse, Nystagmus, Test of Skew (HINTS) ‘Plus' (added test of auditory function) examination consists of four pieces of the bedside examination which accurately differentiates central and vestibular causes of acute vestibular syndrome (acute prolonged vertigo, spontaneous nystagmus, imbalance, nausea/vomiting, head motion intolerance). A benign exam (usually indicative of acute vestibular neuritis) consists of: 1) unidirectional, contralesional, mixed horizontal-torsional nystagmus; 2) an abnormal ipsilesional HIT; 3) no evidence of skew deviation on alternate cover testing; 4) normal hearing. When hearing is involved, labyrinthine ischemia should be strongly considered, especially in someone with vascular risk factors without clear evidence of infectious labyrinthitis or Ramsay Hunt syndrome. The presence of a hypertropia in the setting of acute vertigo is generally assumed to represent a skew deviation until proven otherwise, and this is suggestive of central utricle pathway injury (rarely, a patient can have a "peripheral" skew due to involvement of the utricle within the labyrinth or utricle fibers in the 8th cranial nerve). Left hypotropia could accompany an abnormal HIT to the left with a left vestibular nuclear lesion (caudal to the decussation of the utricle-ocular motor pathways) and rarely due to left-sided 8th nerve/labyrinthine injury. B. Incorrect. In this case, the left-beating nystagmus in left gaze would be consistent with bidirectional, direction-changing or gaze evoked nystagmus (GEN) since there was right-beating nystagmus in right gaze. In peripheral disorders, the spontaneous right-beating nystagmus would increase in the direction of the fast phase (in accordance with Alexander's law) or to the right, but should not transition to left-beating in left gaze. Commonly, horizontal GEN is seen with pathology involving the medial vestibular nucleus, nucleus prepositus hypoglossi, or cerebellar flocculus (or their connections). A normal HIT is also highly suggestive of a central etiology, commonly a posterior inferior cerebellar artery distribution infarct. A right hypertropia increasing in left and downgaze and in right head tilt would be most consistent with a right 4th nerve palsy (especially if there is excycloduction in the right eye). Occasionally an unrelated congenital or longstanding acquired 4th nerve palsy can lead to a falsely "central" HINTS exam, as any hyperdeviation seen with alternate cover testing should be assumed to be a skew deviation until proven otherwise in the acutely vertiginous patient. Rarely, a nuclear or fascicular 4th nerve palsy can be accompanied by dizziness/vertigo or imbalance and nystagmus (especially with involvement of the adjacent brachium conjunctivum, also known as the superior cerebellar peduncle). C. Incorrect. Concerning findings in this case include gaze-evoked nystagmus and acute hearing loss. The internal auditory artery, a branch of the anterior inferior cerebellar artery, supplies the cochlea and vestibular inner ear structures. Therefore, examination findings as above must be treated as a stroke equivalent. D. Correct. These features are all compatible with left unilateral vestibular loss, which in the acute setting, is usually due to vestibular neuritis. Summary of case and diagnosis (watch the remainder of the video): Additional findings include left-beating nystagmus in left gaze and up-beating nystagmus in upgaze (GEN); and abnormal HIT to both sides, more prominent on the left than the right; she also presented with a hypertropia and vertical diplopia, which quickly resolved within 24 hours. As discussed above, the combination of these findings is most consistent with a central etiology. In her case, she suffered a spontaneous hemorrhage mainly involving the right middle cerebellar peduncle due to anti-coagulation. There was also involvement of the right flocculus, and it has been shown that with acute unilateral flocculus strokes, the vestibulo-ocular reflex (VOR) is often impaired contralesionally more than ipsilesionally. Not only were the corrective (overt) saccades more prominent to the left than to the right with bedside testing, but with video HIT testing, the gain (calculated as area under the eye velocity curve [green traces] to the area under the head velocity curve) to the left was 0.44 while it was 0.57 to the right. Generally, gains of <0.7 are considered abnormal. Right flocculus involvement is the most likely explanation for an abnormal HIT to the left. It is also likely that the fascicle of cranial nerve 8 was injured on the right side, which might provide another explanation for ipsilesional VOR hypofunction. A normal HIT is highly suggestive of a central process, but an abnormal HIT can be seen with central etiologies.