Periodic alternating nystagmus in phenytoin intoxication.

A patient with alcoholic cerebellar degeneration had periodic alternating nystagmus during a period of phenytoin intoxication. The nystagmus resolved as the serum phenytoin level fell, as demonstrated by electronystagmography. Periodic alternating nystagmus generally implies structural brainstem disease, especially at the craniocervical junction. To our knowledge, its drug-related occurrence has not been previously reported.