Acquired pendular nystagmus associated with the lesion of tegmentum mesencephali in a patient with probable multiple sclerosis

: A 42-year old woman was admitted to our hospital because of sudden onset of dizziness and oscillopsia. Neurologic examination revealed horizontal, binocular pendular nystagmus, which increase their amplitude on left lateral gaze. She also showed that mild right blephaloptosis, right facial spasms, increased tendon reflexes and positive pathological reflexes of four limbs and mild chorea-like movement of both feet. MRI showed an abnormal high intensity area on a T2weighted and proton density images located at the right tegmentum mesencephali. She was diagnosed as clinically probable multiple sclerosis according to the Poser's criteria. The nystagmus was suppressed by clonazepam and diazepam. To our knowledge, it is a first report of acquired pendular nystagmus associated with the lesion of tegmentum mesencephali. We speculate that the involvement of the tract of paramedian pontine reticular formation causes the nystagmus and the dysfunction of GABAnergic neurons might play an important role of the nystagmus.