Central positional nystagmus due to acute medial medullary infarction

A 70-year-old male with risk factors for vascular disease presented with dizziness and instability. The patient showed horizontal geotropic nystagmus when turning his head while lying down, with larger slow phase velocity observed when turning to the left. There were no other neurological deficits. Video head impulse tests and vestibular evoked myogenic potentials were normal. The initial magnetic resonance imaging (MRI) findings were negative; however, the patient experienced subsequent right-side weakness, right tilting, and recurrent episodes of vertigo. A follow-up MRI revealed an acute left medial medullary infarction, which seems to have caused the paroxysmal geotropic central positional nystagmus in this patient.