Editors' note: Teaching Video NeuroImages: Vestibulo-ocular reflex defect in cerebellar stroke

Abstract

In “Teaching Video NeuroImages: Vestibulo-ocular reflex defect in cerebellar stroke,” Witsch et al. described a patient with an abnormal vestibulo-ocular reflex with corrective saccade on right head impulse test (HIT) found to have a left flocculonodular cerebellar stroke. They commented that an abnormal HIT is generally associated with peripheral pathology, but that their patient demonstrated that this test has “limited specificity.” On review of this patient's MRI, Lee et al. commented that the lesion is, in fact, posterolateral to the flocculonodular lobe and could not easily explain an abnormal vestibulo-ocular reflex. Tarnutzer et al. agree and note that the lesion is in the region of the cerebellar hemisphere fed by the superior cerebellar artery. Furthermore, they add that the HIT test's specificity is 85%–90%, which is not “limited.” In addition, Chen et al. note that they demonstrated that quantitative HIT can produce a corrective saccade in the setting of cerebellar stroke, even with a normal vestibulo-ocular reflex. Witsch et al. respond that: (1) Their interpretation of the MRI was that the stroke was in the inferior and middle cerebellum (the flocculonodular region), not the flocculonodular lobe; (2) Occam's razor suggests that this lesion must be the explanation for the abnormal vestibulo-occular reflex; (3) It may have been more accurate to say that their finding “refutes the common perception of absolute specificity” of the HIT, rather than saying that HIT has “limited specificity;” and (4) The portable video HIT could be helpful in identifying those patients who have cerebellar infarcts with normal vestibulo-ocular reflex gain but catch-up saccades. In “Teaching Video NeuroImages: Vestibulo-ocular reflex defect in cerebellar stroke,” Witsch et al. described a patient with an abnormal vestibulo-ocular reflex with corrective saccade on right head impulse test (HIT) found to have a left flocculonodular cerebellar stroke. They commented that an abnormal HIT is generally associated with peripheral pathology, but that their patient demonstrated that this test has “limited specificity.” On review of this patient's MRI, Lee et al. commented that the lesion is, in fact, posterolateral to the flocculonodular lobe and could not easily explain an abnormal vestibulo-ocular reflex.