Spontaneous Horizontal Jerk and Direction Changing Infantile and Latent Nystagmus in an Adult

While patients with infantile nystagmus often display both jerk and pendular nystagmus waveforms, this patient had spontaneous and direction changing horizontal jerk nystagmus. When looking up and down, the nystagmus stayed horizontal, which is typical of infantile nystagmus, vestibular nystagmus, and periodic alternating nystagmus (PAN) among others. Also typical of infantile nystagmus, there was a slight decrease in the spontaneous nystagmus with convergence, and with eye movement recordings, there were velocity increasing slow phase waveforms (which can often be appreciated at the bedside without eye tracking equipment). At times the spontaneous nystagmus seemed to alternate between right and left-beating, but this was not PAN; instead, this was a result of the patient switching visual fixation between the eyes, which produced a latent nystagmus - e.g., right-beating with the right eye viewing and left-beating with the left eye viewing. At first glance, this pattern of spontaneous horizontal nystagmus that changed direction with lateral viewing resembled a central pattern of nystagmus as in the acute vestibular syndrome. However, this patient was asymptomatic without oscillopsia or vertigo, making a vestibular etiology very unlikely.