Periodic alternating nystagmus associated with periodic alternating skew deviation.

A 34-year-old man had both periodic alternating nystagmus and periodic alternating skew deviation. Neurologic examination and cranial computed tomography supported the diagnosis of cerebellar degeneration. Pathophysiologic mechanisms of these motility disturbances are discussed briefly. To our knowledge these two unusual eye movement abnormalities have not been reported previously in the same patient.