Vestibular dysfunction after cochlear implantation.

Objective: To determine the prevalence, symptom characteristics, and potential risk factors for vestibular symptoms after cochlear implantation.
Study Design: Case-control study design embedded within an ongoing cohort of patients undergoing implantation.
Setting: Academic medical center cochlear implant research program funded by the National Institutes of Health.
Patients: Seventy five eligible consecutive patients undergoing cochlear implantation.
Intervention: Medical record review.
Main Outcome Measure: Recorded symptoms of vestibular symptoms after cochlear implantation. Subjects with vestibular symptoms were considered case subjects; those without vestibular symptoms were considered control subjects.
Results: Twenty-nine of 75 (39%) patients experienced dizziness postoperatively. Four patients experienced a single, transient acute vertigo attack occurring less than 24 hours after surgery. The majority, 25 patients, experienced delayed, episodic onset of vertigo. The median (interquartile range) time of delayed onset was 74 (26-377) days after implantation. Delayed dizziness manifested as spontaneous episodic or positional vertigo. Preoperative dizziness, age at implantation, and age at onset of hearing loss were significantly greater in the dizzy group. Preoperative electronystagmography did not differentiate between groups.
Conclusions: Thirty-nine percent (29/75) of subjects with implants were dizzy after implantation. The majority of subjects experienced dizziness in a delayed episodic fashion. Dizziness was not related to implant activation. It seemed that delayed dizziness was not related to immediate surgical intervention but could result from chronic changes occurring in the inner ear; there was some suggestion this could take the form of endolymphatic hydrops.