Transient upbeat nystagmus due to unilateral focal pontine infarction.

Upbeat nystagmus is known to be caused by an imbalance of the vertical vestibulo-ocular reflex (VOR), favoring downward VOR activity, due to bilateral lesions of the medulla, ventral tegmentum, anterior cerebellar vermis, adjacent brachium conjunctivum and the midbrain. We report on two patients who had transient upbeat nystagmus due to unilateral pontine infarction that may have disrupted bilateral upward VOR pathways running in the ventral tegmental tracts.