STIMULUS-INADEQUATE SENSATIONS IN COCHLEAR IMPLANT PATIENTS

From August 1984 to April 1987 the Department of Otolaryngology at the Medizinische Hochschule in Hannover implanted the NUCLEUS 22 channel cochlear implant system (CI) in their first 56 adults. Since implantat ion, 27 (51%) patients have described undesireable sensations from the ir implant. These were defined as stimulus-inadequate sensations (SIS) and were classified into three types: 1) painlike sensations; 2) high -frequency sensations; and 3) non-stimulation. Twenty-three patients w ere radiographically investigated by polytomography. All of the intrac ochlear electrodes were visualised and a correlation between SIS and t he radiological findings was established. It was found that i) SIS sim ilar to pain are caused by electrical stimulation of the mucous membra nes and periosteum of the tympanic cavity; ii) the high-frequency SIS seemed to be due to non-physiological electrical stimulation of the ba sal ganglion cells; and iii) the reason for non-stimulation is probabl y damaged electrodes and fibrosis around the electrode. Conventional t omography is the method of choice for estimating the number and config uration of intracochlear electrodes.