[A case of up-beat nystagmus associated with Chiari malformation type I (author's transl)].

A case of Chiari malformation type 1 with sign of upbeat nystagmus was reported. The patient was a 9-year-old girl who was admitted to the Department of Neurosurgery with the chief complaints of snoring and headaches. The neurological examination on admission revealed a lower cranial nerve disturbance bilaterally and upbeat nystagmus in the primary ocular position that increased in amplitude upon gazing upward, and horizontal nystagmus on gazing laterally. The skull tomogram showed platybasia. The vertebral arteriogram and the pneumoencephalotomogram showed downward displacement of cerebellar tonsils to the level of C2. The patient received suboccipital craniectomy and C1, C2 laminectomy for decompression and the foramen of Majendie was opened. From the operative findings the diagnosis was confirmed as Chiari malformation type 1. In the first two postoperative weeks, the upbeat nystagmus as well as other symptoms was gradually improved. It was therefore considered that the responsible lesion of the upbeat nystagmus in this case might be in the lower brain stem or the inferior vermis due to mechanical compression or circulatory disturbance.