[A case of non-paralytic pontine exotropia due to pontine tegmentum lesion confirmed by magnetic resonance imaging and electronystagmography].

A case with non-paralytic pontine exotropia (NPPE) due to brainstem infarction is reported. A 77-year-old hypertensive man suddenly developed dizziness, double vision, dysarthria, and right ataxic hemiparesis. Oculomotor findings on admission consisted of: (1) full right exotropia in the primary position; (2) complete adductive paralysis of the left eye with slight preservation of convergence; (3) tonic deviation of the right eye to the full abducting position with right-beating nystagmus after an immediate forward gaze. The leftward saccades showed multiple saccades with slow velocity on electronystagmography (ENG). The right exotropia disappeared and the slight adductive paresis of the left eye remained with right monocular nystagmus seven weeks after the onset. Magnetic resonance imaging (MRI), which was performed nine weeks after the onset, disclosed a small lesion with high intensity involving the left medial longitudinal fasciculus (MLF) on T2-weighted spin echo image. The leftward saccades showed multiple saccades with normal velocity eleven weeks after the onset. The hypofunction of unilateral PPRF with ipsilateral MLF lesion probably causes the contralateral NPPE.