VESTIBULAR EFFECTS ASSOCIATED WITH IMPLANTATION OF A MULTIPLE-CHANNELCOCHLEAR PROSTHESIS

This study revealed that some patients with cochlear implants have sym ptoms of vertigo and imbalance following implant surgery. Although mos t experience a resolution of these symptoms, some patients have more p ersistent disturbances of balance. A total of 52 patients were implant ed with a Nucleus 22 channel cochlear implant device between September 1988 and February 1994. Preoperatively, all but five of the patients received a vestibular evaluation. Twenty-two of the 52 patients receiv ed both pre- and postoperative vestibular evaluation. The cochlear imp lant was worn and activated during the postoperative vestibular assess ment. The vestibular assessment included electronystagmography, comput erized dynamic posturography, and harmonic acceleration testing. Five of the 22 patients demonstrated bilateral vestibular weakness preopera tively; that is, no response to caloric stimulation or a total of less than 30 degrees per second for the four irrigations. These patients w ere not included in the caloric analysis portion of the study. The rem aining 17 were divided into groups under 60 years of age (7 patients) and over 60 years of age (10 patients). Analysis of the pre-and postop erative caloric response of the implanted ear showed a significant dro p in output for the group over 60 years of age. The difference for the group under 60 years of age was not significant. Forty percent of the patients in the over 60 age group and 43% of those in the under 60 ag e group developed a peripheral vestibular weakness postoperatively. Ho wever, younger individuals in general did not seem to have balance com plaints and did not require vestibular rehabilitation as frequently as the older group. Potential cochlear implant candidates should be advi sed of the possibility of postoperative vestibular effects following c ochlear implantation. Most of the symptoms are transient; however, the re may be persistent symptoms of imbalance that may be benefited by ve stibular rehabilitation.