Novel therapies related to cochlear implants.

Intra-cochlear drug delivery may represent a key issue in cochlear implant (CI) success in the future. Its therapeutic goals include the improvement of hearing preservation by reduction of insertion trauma and intra-cochlear tissue growth. Other benefits of intracochlear drug delivery include improvements of the auditory nerve status and of the electrode/nerve interface. A number of potential drug delivery devices are currently under development including drug release using electrode arrays. Among the drugs involved, dexamethasone has been shown to reduce the hearing loss due to mild cochlear implant insertion trauma (Kiefer et al 2010). Based on this evidence we evaluated the effects of intratympanic insertion of 10% dexamethasone-eluting silicone rods in animal models of both minimal and severe insertion trauma. With the purpose of verifying the hearing protection, the effect on tissue growth and the cochleostomy healing, we used 2 different types of electrode array designed to create either minimal or severe insertion trauma. In one group guinea pigs were gently implanted with soft rods constructed only from silicone, while in the other animals were implanted with a stiffer array containing stiff wire and causing mechanical trauma. In each case, 10% dexamethasone-eluting rods were evaluated for therapeutic benefit and non-eluting rods were implanted as controls. Implantations were performed through a 0.7mm cochleostomy, followed by 3-mm deep rod insertion. Hearing threshold audiograms were acquired prior to implantation and during the next two/four/eight weeks by recording compound action potentials with electrodes near the round window. After these periods the cochlea was removed, decalcified, embedded in paraffin and longitudinally cut into 5-μm thick sections. For each sample we examined the Scala Tympani occlusion in the cochlear basal turn, and the cochleostomy healing. Audiological and histological results showed no significant differences in hearing protection between non-eluting or 10% dexamethasone-eluting rods within 60 days. No bacterial contamination was detected in the implant rods. However, in presence of 10% dexamethasone-eluting tubes, the average tissue growth was always lower in comparison to non eluting ones, in particular we observed a significant reduction in the new bone. This data supports the use of steroid eluting rods with slow-release as an antiinflammatory additive in cochlear implants. The poor hearing preservation obtained under these conditions is under further histological investigation.