Caloric-induced nystagmus with isoelectric electroencephalogram

Area of Science:

• Neuroscience
• Clinical Neurology
• Vestibular System

Background:

• Caloric vestibular testing (CVT) normally elicits nystagmus.
• Nystagmus has been observed in patients with persistent vegetative states and intact brainstem reflexes.
• No prior reports exist of CVT-induced nystagmus in patients with an isoelectric electroencephalogram (EEG).

Observation:

• A patient who experienced cardiopulmonary arrest presented with an isoelectric EEG.
• Despite the isoelectric EEG, caloric vestibular testing was performed.
• Nystagmus was observed during caloric vestibular testing in this patient.

Findings:

• This case demonstrates that caloric-induced nystagmus can occur in the absence of cortical activity (isoelectric EEG).
• Animal studies suggest the paramedian pontine reticular formation generates horizontal saccades and the quick phase of nystagmus.
• The findings support the hypothesis that caloric-induced nystagmus has a rudimentary origin in the brainstem.

Implications:

• This challenges the assumption that cortical function is necessary for all components of the nystagmus response to CVT.
• The brainstem's role in generating caloric-induced nystagmus is highlighted, even in profound states of brain dysfunction.
• Further research into brainstem reflexes in critically ill patients is warranted.