gms | German Medical Science

Most cochlear implant manufactures are offering the possibility to measure the electrically evoked compound action potential (ECAP) via the inserted electrode array. The ECAP threshold is widely used for fitting the speech processor to small children and also to adults. In subjects with a Nucleus RE24CA implant the ECAP threshold is about 15CL above the comfort (C-) level. Usually, the subject will have a hearing sensation at those levels.

We are presenting a case of a man with hearing loss at both ears and a congenital malformation of the cochlea. There was a clear indication for cochlea implantation due to positive promontory test and a hearing nerve visible in the MRI. At the age of 30 he received a cochlear implant. The examination of the patient showed both correct electrode placement (X-ray) and possibility to stimulate the hearing nerve (ECAP- and E-BERA responses).

During the first week of initial fitting as well as one month later the ECAP thresholds were found via NRT measurement at each of the 22 electrode contacts. At five electrode contacts (22, 20, 15, 10 and 5) amplitude growth functions were recorded. During the fitting, even C-levels 40CL above the ECAP threshold didn’t lead to hearing sensation but caused unpleasantness. During the next five weeks, we tried to get the subject accustomed to higher stimulation levels without unpleasant side-effects. In the end, this aim was achieved but the subject remained without any hearing sensation.

Conclusion: despite clear indication for a cochlear implant and intra- and postoperative evidence of a coupling of the implant to the hearing nerve, a hearing sensation can fail to occur in certain subjects.