Periodic Alternating Nystagmus Due to a Chiari Malformation - The Role of the Vestibulocerebellum in Ocular Motor Function

We describe a 53-year-old woman presenting with oscillopsia and ocular motor abnormalities due to a Chiari I malformation, in the absence of headaches. The vestibulocerebellum can be thought of as two functional units: 1) flocculus/paraflocculus (tonsil) and 2) nodulus/uvula. Our patient presented with oscillopsia from periodic alternating nystagmus (PAN) due to nodulus/uvula compression as well as saccadic smooth pursuit and gazeevoked nystagmus due to tonsillar herniation. We highlight the localizing value of several vestibulocerebellar ocular motor findings.