Mesencephalic bilateral horizontal gaze palsies.

An 81-year-old man with diabetes developed dizziness and markedly limited lateral saccades in both directions (figure, A and C, and video 1 on the Neurology Web site at www.neurology.org), but preserved pursuit and vestibuloocular movements (VOR, accompanied with back-up saccades; videos 2– 4). Diffusionweighted MRI revealed a small high-signal lesion at the ventral paramedian midbrain between cerebral peduncles (figure, E), probably reflecting bilateral involvements of the ventral pedunculotegmental pathway—one of the three corticofugal pathways for horizontal saccades—coursing through the medial aspect of cerebral peduncle.1 The abnormally higher VOR gain suggested this pathway might inhibit VOR. Whereas reflexive pursuit conveys signals through the posterior cerebral peduncle, it was spared.2 His vertical gaze also appeared limited (up more so than down), implying the involvement of riMLF but not demonstrated in MRI. The patient recovered in 3 weeks.