[Predominantly ipsilateral smooth pursuit impairment associated with a lesion in the basal pons]

In contrast to the well-defined brainstem centers for saccades and eye reflexes, the brainstem centers mediating smooth pursuit eye movements are poorly understood. In monkeys, unilateral damage to the basal pons impairs horizontal smooth pursuit in the direction of the side of the lesion. The major source of afferents to the basal pons is the middle temporal area (MT). The dorsolateral pontine nucleus (DLPN) in the basal pons is considered to be the major gateway for smooth pursuit related signals to the contralateral flocculus. In humans, only one patient was found to have a unilateral lesion in the basal pons and selective impairment of smooth pursuit toward the side of the lesion. We report a 34-year-old man with a lesion in the basal pons identified by MRI. He had suffered from recurrent oral aphthosis, erythema nodosum and enterocolitis, and was hospitalized because of dysarthria. He was clinically diagnosed as neuro-Behçet disease. Saccades, smooth pursuit, vestibulo-ocular reflex (VOR), and VOR cancellation were measured. Ipsilateral smooth pursuit eye movements were predominantly impaired and interrupted by saccades, whereas VOR cancellation was impaired in both directions, in contrast with normal saccades and VOR. This observation of predominantly ipsilateral smooth pursuit impairment after a lesion in the human basal pons suggests that the concept of a middle temporal-ponto-floccular pathway for smooth pursuit, previously established in monkeys, can be extended to humans.(ABSTRACT TRUNCATED AT 250 WORDS)