Background: Cochlear implantation (CI) has proven in long term prospective trials to reduce significantly incapacitating tinnitus in single sided deafness (SSD). Discussion arises whether electrical stimulation near the round window (RW) is also able to reduce tinnitus.
Aim: to assess whether electrical stimulation of the basal first 4 intracochlear electrodes of a CI could sufficiently reduce tinnitus and to compare these results with stimulation with all CI electrodes.
Material and methods: 7 patients who met the criteria of severe tinnitus due to SSD were implanted with a Med-El Sonata Ti100 with a FlexSoftTM or Flex24TM electrode. After 4 weeks only the basal electrode pair (E12) nearest to the RW was activated. Each week the following pair was activated until the 4th pair.Thereafter all electrodes were activated. Tinnitus was assessed before CI surgery and before each electrode pair was activated. When all electrodes were fitted, evaluation was done after 1, 3 and 6 months.Tinnitus was assessed with Visual Analogue Scale (VAS) for loudness, psychoacoustic tinnitus loudness comparison at 1 kHz and Tinnitus Questionnaire (TQ) for the effect on quality of life. To evaluate the natural evolution, a tightly matched control group with severe tinnitus due to SSD was followed prospectively.
Results: All the tinnitus outcome measures remained unchanged with 1, 2, 3 or 4 activated electrode pairs. With complete CI activation, the tinnitus decreased significantly comparable with earlier reports.Pre-implantation the tinnitus loudness was 8.2/10 on the VAS and was reduced to 4.1/10 6 months postimplantation.Psychometrically the loudness level went from 21.7 dB SL (SD: 16.02) to 7.5 dB SL (SD: 5.24)and the TQ from 60/84 to 39/84. The non-implanted group had no decrease of the tinnitus, the average VAS remained stable at 8.9/10 throughout the follow-up period of 6 months.
Conclusion: with the current stimulation parameters electrical stimulation in the first 8e10 mm of the basal part of the scala tympani is insufficient to reduce tinnitus. However, stimulation over the complete CI length yields immediate tinnitus reduction confirming earlier results.