Periodic alternating nystagmus associated with Arnold-Chiari malformation.

The Arnold-Chiari malformation type I is a rare congenital condition characterized by herniation of the cerebellar tonsils into the upper cervical spinal tract. Various otoneurological manifestations occur in patients with the disease, which has usually been associated with a downbeat type of nystagmus. In this paper a case with this condition is reported presenting with periodic alternating nystagmus (PAN), which is a rare type of nystagmus observed in diseases of the central nervous system of different pathologies. The patient had a complete otoneurological examination and vestibular function testing. Diagnosis was established by using magnetic resonance imaging (MRI).