Upbeating nystagmus resulting from anticonvulsant intoxication. Report of a case

A rare case of upbeating nystagmus, which occurred under the condition of a loss of visual fixation, due to anticonvulsant intoxication is reported. This patient, a 29 year old male, suffered from grand mal epilepsy for about 12 years, and he had been treated with anticonvulsive drugs. Although a neurological evaluation by a neurosurgeon could suggest the presence of a vague cerebellar sign, neuro-otological evaluation disclosed diverse abnormal findings which clearly demonstrated the presence of dysfunction in the cerebellar system, especially of the verminal and flocculonodular lobe lesion. This may indicate that the anticonvulsive drug affected the vermis and flocculonodular lobe much more than the hemisphere of cerebellum, or that the cerebellar system sign in verminal and flocculonodular lobe lesion and its connection is detected more easily than the hemispheric lesion with the aid of a neuro-otological examination. It was presumed that the upbeating nystagmus in this case was elicited from the lesion of the anterior vermis of the cerebellum and/or its connections. Usefulness and sensitivity of the neuro-otological examination in the field of dysequilibrium of central disorder as well as peripheral vestibular disorder is emphasized.