Perverted head shaking nystagmus in focal pontine infarction.

Although several papers have been published on perverted head shaking nystagmus (PHSN) associated with focal brainstem or cerebellar lesion, there are no reports of a focal pontine infarct that causes PHSN. We report a patient with focal pontine infarction who presented with sustained dizziness, limb dysmetria on the left extremity, decreased sensations to position and vibration of the left extremity, and gait imbalance. Only vestibular abnormality was downbeat nystagmus after vigorous head shakings. The maximum slow phase velocity of PHSN was 26°/s, and its duration was about 20s. This is the first report of PHSN associated with focal pontine infarction. Crossed ventral tegmental tract and velocity storage mechanism of vestibulocerebellum might be related on PHSN in this case.