Periodic alternating nystagmus during caloric stimulation

Area of Science:

• Ophthalmology
• Neurology
• Vestibular System

Background:

• Periodic alternating nystagmus (PAN) is a specific type of horizontal jerk nystagmus with directional reversals.
• Understanding the underlying mechanisms of PAN is crucial for diagnosing and managing related vestibular disorders.

Observation:

• A 75-year-old male presented with a floating sensation and was referred for evaluation.
• Standard gaze and positional testing revealed no nystagmus, but weak right-beating horizontal nystagmus was noted during a left Dix-Hallpike maneuver.
• Electronystagmography and optokinetic nystagmus tests were normal.

Findings:

• During caloric stimulation of the right ear, nystagmus direction periodically reversed from leftward to rightward, repeating 15 times.
• Magnetic resonance imaging showed only chronic ischemia, with no significant focal lesions.
• The patient likely had a latent velocity storage deficit, manifesting as transient PAN upon caloric challenge.

Implications:

• Caloric stimulation is a valuable and straightforward method for uncovering latent eye movement abnormalities.
• This case highlights the utility of caloric testing in identifying impaired velocity storage mechanisms.
• Prompt identification of such disorders can lead to better patient management and outcomes.