[A case of brainstem infarction presenting with paralytic pontine exotropia and non-paralytic pontine exotropia].

We reported a patient with brainstem infarction who presented paralytic pontine exotropia (PPE) in acute phase and non-paralytic pontine exotropia (NPPE) during the recovery phase. On March 10, 1991, a 60-year-old man was brought to our hospital with chief complaints of double vision and right hemiparesis. The ocular position of the left eye on forward gaze was fixed at the midline, while the right eye was abducted, and skew deviation was observed. On leftward gaze, neither eye could pass the midline, and on rightward gaze the right eye was abducted and monocular nystagmus was noted in the abducted right eye, which indicated paralytic pontine exotropia. T2-weighted MRI showed high signal intensity lesions in the left paramedian portion of the mid-pontine tegmentum beneath the fourth ventricle, and in the midline of the pontine base extending to the left side. The next day, similar disturbance of ocular movement was seen on rightward gaze, but the limitation of leftward gaze had improved and NPPE was noted to have developed. On the third day, there was no abduction of the right eye on forward gaze, but left MLF syndrome was still present. Seven days later, the disturbances of ocular movement disappeared. The lesion was considered to be due to partial impairment of the left paramedian pontine reticular formation in addition to the MLF. PPE caused by ischemia due to the perforating arteries of the brainstem, different from that due to basilar artery occlusion may recover after progression through NPPE and MLF syndromes. Hence, one-and-a-half syndrome, PPE, NPPE, and MLF syndromes are considered to be analogous to one another.