Pure upbeat nystagmus in association with bilateral internuclear ophthalmoplegia.

A 66-year-old man developed primary position upbeat nystagmus and bilateral internuclear ophthalmoplegia (INO). Video-oculography showed primary position upbeat nystagmus with exponentially decreasing slow phases, which disappeared in darkness. Brain MRI disclosed enhancing lesions involving bilateral dorsomedial pons extending from the middle to upper portion. Upbeat nystagmus in association with bilateral INO may be attributed by the damage of the cell groups of the paramedian tracts (PMT), the projections from the interstitial nucleus of Cajal (INC) to PMT, or the connections between INC and the nucleus of Roller.