[Complex eye movement disturbance in thalamic and mesencephalic infarcts]

A 36 year-old male patient developed sudden double vision and gait imbalance. Neurological examination revealed gaze paresis upward and on the left side downward (vertical "one-and-a-half"-syndrome), horizontal gaze nystagmus on the left bulbus directed to left. The MRI revealed bilateral thalamic and left midbrain ischemic lesions. The brainstem auditory and visual evoked responses were normally configured. Optokinetic nystagmus test found rightward, upward and downward hypometric saccades, convergence-retraction nystagmus--which was not visible at physical neurological examination--saccadic smooth pursuit eye movement and pseudoabducent palsy on both sides. The complex gaze disturbance was attributed to the lesions in the intralaminar nuclei of the thalamus and in the pretectal and rostromedial tegmentum of the mesencephalon. Infarcts may have been due to a variant artery: i.e. the thalamoperforant and the superior paramedian mesencephalic arteries originate with common branch from one of the communicant basilar artery. The authors discuss the mechanism of complex gaze palsy and call attention to the diagnostic value of optokinetic nystagmus examination.