Jerky seesaw nystagmus in isolated internuclear ophthalmoplegia from focal pontine lesion

Abstract

Dissociated abducting nystagmus of the contralesional eye on attempted gaze to the contralesional side is typical of internuclear ophthalmoplegia (INO).1 Rarely, dissociated torsional-vertical nystagmus, usually downbeat in the ipsilateral eye and intorsional in the contralateral eye,2,3 or ipsilesional torsional nystagmus4,5 may occur in INO. We report a patient with isolated INO and jerky seesaw nystagmus from a focal pontine lesion and discuss possible mechanisms of various torsional-vertical nystagmus accompanying INO. A 47-old-woman was admitted with sudden vertigo and oscillopsia. She had diabetes mellitus and previous history of left corona radiata infarction. On admission, she could hardly open the eyes owing to severe oscillopsia. In neutral gaze, she showed extorsional downbeat nystagmus in the right eye synchronous with intorsional upbeat nystagmus in the left eye (see the video on the Neurology Web site at www.neurology.org). The nystagmus was changed into mainly upbeating on upward gaze. On leftward gaze, she also showed adduction paresis of the right eye with dissociated abducting nystagmus in the left eye (right INO). Convergence was mildly impaired, probably from oscillopsia. Head tilt or skew deviation was not evident. The remainder of the neurologic examination was unrevealing. MRI of the brain disclosed a tiny lesion in the right dorsomedial pontine tegmentum, which corresponds to the known anatomic location of the medial longitudinal fasciculus (MLF) (figure, A through C; see page …