The association of periodic alternating nystagmus with periodic alternating gaze. A case report.

A 26-year-old man with a recurrent cerebellar medulloblastoma developed periodic alternating nystagmus. During radiation treatment, a bilateral voluntary horizontal gaze paresis appeared, and the periodic alternating nystagmus was replaced by periodic alternating gaze. Several days later, full eye movements returned, as did the periodic alternating nystagmus which had an identical periodicity to the periodic alternating gaze. The underlying pathophysiology of periodic alternating nystagmus and periodic alternating gaze is discussed.