[A case of bilateral medial longitudinal fasciculus (MLF) syndrome associated with rotatory nystagmus].

We report a patient with bilateral MLF syndrome associated with rotatory nystagmus. The patient was a 33-year-old female, admitted to our hospital because of sudden onset of diplopia. The adduction of both eyes were markedly disturbed on lateral gaze, but convergence was relatively spared. Excyclorotatory nystagmus was observed in the right eye on the rightward gaze, and gaze-directional horizontal gaze nystagmus was observed in the left eye on the leftward gaze. No other neurological abnormality was pointed out. T2-weighted magnetic resonance imaging revealed a high intensity lesion in the pontine tegmentum. The lesion was located at the mid-pontine level. Rotatory nystagmus has been rarely observed in the patients with MLF syndrome, and previous authors postulated a lesion in the MLF above the level of the abducens nucleus and below the level of the trochlear nucleus. In our patient we demonstrated a lesion in the hypothesized location on magnetic resonance imaging and provided a supportive anatomical evidence.