Non-auditory stimulation in adult cochlear implant users.

This is a retrospective case review of all 163 adults to have received multichannel cochlear implants on the Manchester University/Manchester Royal Infirmary programme between 1988 and 1998. The aims were to investigate the incidence of unwanted non-auditory effects of electrical stimulation (NAS) of the cochlea, and to try to identify any factors that seemed to be related to these effects. The effectiveness of programming strategies in eliminating unwanted effects was also studied. Most of the devices were Nucleus CI 22M or CI 24M. The remainder were Med-el Combi 40 or Combi 40+. NAS occurred in 23.9% of implantees. There were 20 cases of facial nerve stimulation (12.3%), 18 cases of pain in the ear or throat (11.0%) and one case of vestibulospinal spinal stimulation (0.6%). Two aetiologies were significantly associated with NAS. Otosclerosis tended to be associated with facial nerve stimulation and skull base fracture was associated with pain. Pain was associated with electrodes stimulated in the base turn of the cochlea and facial nerve stimulation tended to occur with more distally situated electrodes, close to labyrinthine segment of the nerve. There was no association with one particular make of device. The T and C levels for the rogue electrodes were in the normal range. It is concluded that the unwanted effects result from shorting of current through areas of low electrical resistance in the temporal bone. A number of different strategies were employed to prevent the effect, including alteration of current levels, removal of electrodes from the map and changing the stimulation mode, and this was successfully achieved in all cases. There was no difference between the performance of patients who had had NAS and those who had not, as assessed on open-set BKB sentence scores.