Non-Paralytic Pontine Exotropia as a Predominant Sign of Brainstem Infarction - A Case Report

The association of internuclear ophthalmoplegia (INO) with exotropia in the contralateral eye is a rare finding, known as non-paralytic pontine exotropia (NPPE). We report a case of an 80-year-old woman with acute onset of diplopia on admission who presented with left eye exotropia with left-beating nystagmus whilst fixating with the right eye and inability to adduct the right eye on left gaze. Brain magnetic resonance imaging showed two small areas of vertebrobasilar territory ischaemic stroke, one beneath the inferior portion of the aqueduct and another in the right occipital lobe. Our case highlights an interesting clinical manifestation of brainstem infarction that, along with ocular motility examination, allowed us to review its pathophysiology, including the influence of the contralateral paramedian pontine reticular formation stimulation in the mechanism of contralateral exotropia in NPPE. The fast clinical resolution of these cases can explain the scarcity of NPPE reports.