Periodic alternating nystagmus in isolated nodular infarction

Periodic alternating nystagmus (PAN) is characterized by periodic reversal of horizontal jerky nystagmus with a null period of several seconds. Damage to the uvulonodulus or to their connections with the brainstem vestibular nuclei has been suggested as a mechanism of PAN.1,2 However, PAN has rarely been reported in circumscribed cerebellar lesion.3 We report a patient with isolated nodular infarction who developed PAN without fixation in association with perverted head-shaking nystagmus (HSN) and loss of tilt suppression of the postrotatory nystagmus. This is the first report of PAN in circumscribed cerebellar infarction, and provides further evidence that PAN occurs due to dysfunction of cerebellar nodulus. A 69-year-old man with a history of hypertension developed acute vertigo with nausea/vomiting and postural imbalance. On examination, we observed spontaneous horizontal nystagmus in the primary position which reversed its direction with a cycle of approximately 2 minutes and a transition period of several seconds by using video Frenzel goggles (SLMED, Seoul, Korea) (see the video on the Neurology Web site at www.neurology.org). The …