The Acute Vestibular Syndrome in MS Due to Middle Cerebellar Peduncle/Root Entry Zone Lesion

This is a 13 year-old girl with relatively abrupt onset vertigo and oscillopsia. On exam, there was primarily right-beating nystagmus in primary gaze with a slight upward (upbeat) component, giving the nystagmus an oblique appearance. The upward component and lack of a clear torsional component acutely makes the nystagmus atypical for a peripheral localization despite a + head impulse test to the left side. Furthermore, her nystagmus was direction changing (gaze-evoked): right-beating in right and down, left-beating in left, up-beating in up. Her acute demyelinating lesion was at the middle cerebellar pendulce and there appeared to be some of the intraparenchymal portion of the 8th cranial nerve, head impulse test (HIT), which generally (but not always) suggests a peripheral localization. While a negative HIT is highly suggestive of a central etiology in the acute vestibular syndrome, a + HIT can be either peripheral or central.