ABSTRACT
A 56 year-old man presented with vertigo and the right sided weakness. Neurological examination revealed a lethargic man with good orientation to three spheres. His neck was supple. He had anisocoria, the right pupil being larger than the left by 1.5 mm with sluggish light reaction bilaterally. He had exotropia of the right eye in primary gaze. The abduction of both eyes were full with terminal horizontal nystagmus. The adduction of both eyes were quite limited in each eye. He had a limited upward gaze with poor convergence. These were interpreted as the syndrome of the medial longitudinal fasciculus (MLF) bilaterally. He had a depressed gag reflex on the right side with tongue deviation to the right. He had a mild weakness of the right side limb and also had the right sided hemihyperesthesia including his face to pain and temperature. Twenty four hours after the onset, the left brachial angiography revealed a complete occlusion of the rostral portion of the basilar artery without visualization of the posterior cerebral and superior cerebellar arteries bilaterally. CT scans three days after the onset revealed a low density area in the mid pons with extension rostrally up to the mesencephalon. Four days later he became quadriplegic with bilateral horizontal gaze palsy. No more internuclear ophthalmoplegia is noted on both sides. The midline location of the MLF in the pons, and the separate blood supplies by different paramedian branches of the basilar artery, form the anatomical explanation for the frequent unilaterality of vascular and bilaterality of demyelinating lesions. Bilateral MLF syndrome has been considered almost pathognomonic of multiple sclerosis.(ABSTRACT TRUNCATED AT 250 WORDS)