Arnold-Chiari malformation in a geriatric patient.

Downbeat nystagmus was the salient clinical manifestation of an Arnold-Chiari malformation in the 74-year-old woman we have described. Interesting features included the patient's age at the time of diagnosis, the sensitivity of downbeating nystagmus as a localizing neuro-ophthalmologic sign, and the value of metrizamide cisternography in defining lesions of the craniocervical junction.