Hidden Electrode Failure in a Cochlear Implant User

When the impedance of an electrode contact is highly increased in a cochlear implant, a failure of the appropriate electrode seems obvious. We present a case where impedances of some electrodes were at the lower edge of the normal range and not regarded as suspicious neither by the clinical fitting software nor by in-vivo tests conducted by the implant manufacturer. However, speech comprehension was substantially degraded and sound perception distorted. Also, on the affected electrodes, loudness perception was compromised and responses of the electrically evoked compound action potential were no longer measureable. After re-implantation, the subjective sound percept was clear again and speech comprehension scored much better than before. Later, inspection of the explant revealed shorts on the device and the implant was classified as device failure. Our case shows the importance of collecting longitudinal data of cochlear implant patients, i.e. device related technical measurements and hearing performance data, and the consideration of all these data in cases of patient complaints or suspected implant failures. Laryngoscope, 131:E1275-E1278, 2021.