[Non-paralytic pontine exotropia with alternating exotropia]

We report a patient with pontine infarction who showed non-paralytic pontine exotropia (NPPE) with alternating exotropia. An 81-year old woman developed diplopia and gait disturbance. On the fourth day, she was admitted to our hospital. Oculomotor findings on admission showed that the ocular position of the left eye on forward gaze was fixed at the midline, while the right eye was abducted. When she was instructed to use the right eye for forward gaze, the left eye deviated outward. On right gaze, the left eye was not abducted and monocular nystagmus was noted in the abducted right eye. Upper gaze was limited in the right eye and convergence was not possible. The remaining ocular movements were intact. On cranial CT performed on eye closure, the left eye was abducted and the right eye was fixed at the midline. Brain MRI showed cerebral infarction located in the left paramedian portion of the middle pontine tegmentum with involvement of the medial longitudinum fasciculus (MLF) and in the ventral site of the upper pons. On the 16th day, right exotropia disappeared on eye opening without forward gaze, but forward gaze easily induced outward deviation of the right eye. On the 39th day, right exotropia on forward gaze had almost disappeared. However, left MLF syndrome and abnormal convergence were persistent when she discharged on the 76th day. In conjunction with oculomotor and neuroradiological findings, the NPPE with alternating exotropia in our patient may be due to severe MLF damage and secondary hyperactivity of the contralateral paramedian pontine reticular formation.