A case of bilateral MLF syndrome with exotropia due to brain stem infarction is reported. A 77-year-oldwoman developed sudden diplopia with dizziness. Ocular motor findings on admission were : On forward gaze, she used only the right eye, and the left eye was in the full abduction position;she could adduct the left eye to the midposition when using it for fixation ; leftward gaze evoked left-beating nystagmus of the left eye, but the right eye did not adduct ; righward gaze evoked right-beating nystagmus of the right eye but the left eye did not adduct; on upward gaze, right eye movement was in-sufficient ; downward gaze was possible ; convergence was insufficient.
MRI (T2 weight spin echo image) displayed a high signal intensity area in the midbrain teg-mentum, but the pons was intact. On the basis of these findings, the diagnosis was intact. On the basis of these findings, the diagnosis was bilateral MLF syndrome with non-paralytic exotropia.
The lesion in this case may be bilateral MLF and right oculomoter nucleus disorder. The exotropia of this patient may have been due to bilatreral dysfunction of the MLF and hyper-function of the left paramedian pontine reticular formation (PPRF).
The difference between paralytic pontine exotropia (PPE) and non-paralytic pontione exotropia (NPPE) is also discussed in this paper.
