Vestibular function in patients with cochlear implantation

The aim of this work was to determine the influence of cochlear implantation (CI) on vestibular canal and otolithic function. Between 1995 and 1999, 15 patients (6 females, 9 males; 9-77 years old) underwent a vestibular examination before and after CI. Electronystagmography was performed between 5 and 8 days after CI in 9 patients, and with a time delay of 2-24 months in 10 patients. Pre- and postoperative evaluation included electronystagmography with caloric (44 degrees C, 30 degrees C, ice-water) and pendular rotatory testing. Otolithic function was measured postoperatively using off-vertical axis rotation (OVAR) in six patients. Preoperative data (n = 14) showed areflexia on caloric and rotatory pendular testing in deafness cases due to meningitis (n = 2) and in 2/5 patients with sudden idiopathic bilateral deafness. Two patients suffering from an idiopathic deafness had a unilateral hyporeflexia. Vestibular function was normal in the other eight patients. Immediately following CI, among patients with normal preoperative canal function, three developed vertiginous symptoms with spontaneous nystagmus, which disappeared within days to weeks. Later, postoperative canal evaluation was normal in 5/8 patients (62%) with initially preserved vestibular function: areflexia was measured ipsilaterally to the implanted ear in 1 patient and contralaterally in 2 patients. Hyporeflexia was measured ipsilateral to the implanted ear in two patients. OVAR examination, performed 2-19 months after surgery, showed a preserved otolithic function in all 6 tested patients. Transient vertigo on electrical CI stimulation was described in only one patient during the first postoperative weeks. The following conclusions can be drawn. Patients with deafness due to meningitis had an eradicated vestibular function. In other etiologies, vestibular function was most often preserved. CI did not usually abolish vestibular function, but the canal function was disturbed temporarily in 20% of cases. Otolithic function was preserved in all six CI patients tested in this series.