Periodic alternating nystagmus.

Horizontal jerk nystagmus is indicative of a disorder involving the vestibular system. Periodic alternating nystagmus is a form of spontaneous nystagmus with a specific pattern. It is identified by the presence of spontaneous nystagmus in the primary direction of gaze, which beats in one direction for 1 or 2 minutes, followed by a null period, and then reappearance of the nystagmus in the opposite direction for a similar length of time. It may be congenital or acquired, and may be seen in association with vestibular-cerebellar disease or loss of vision. Recent case reports indicate that some forms of periodic alternating nystagmus may respond favorably to baclofen therapy.