Direction-fixed and Direction-changing Positional Nystagmus in Ramsay Hunt Syndrome

To investigate the incidence of positional nystagmus (PN) using a head-roll test in patients with Ramsay Hunt syndrome with vertigo (RHS_V) and discuss possible mechanisms.

Retrospective study.

Tertiary referral academic medical center.

Twenty-eight patients with RHS_V were enrolled.

Eye movements were recorded at positions of head roll to the right or left, and PN was classified as direction-fixed or direction-changing. Vestibular function tests including caloric test were performed.

Direction-fixed nystagmus beating away from the affected side was the most common type of PN (61%), followed by direction-changing geotropic type (18%), direction-fixed nystagmus beating toward the affected side (14%), and direction-changing apogeotropic type (7%). The duration of nystagmus was longer than 60 seconds in all patients exhibiting direction-changing PN. Postcontrast T1-weighted internal auditory canal (IAC) magnetic resonance imaging showed enhancement of not only the facial and vestibulocochlear nerves, but also the inner ear structures or dura along the IAC, suggesting inflammatory changes within the labyrinthine membrane or IAC dura.

Although direction-fixed PN was more commonly observed (75%), direction-changing PN was also observed in some RHS_V patients (25%). The mechanism of direction-changing PN may be, at least in part, explained by the alteration of specific gravity of the lateral semicircular canal cupula or endolymph due to inflammation in the inner ear membrane.