Effect of both local and systemically administered dexamethasone on long-term hearing and tissue response in a Guinea pig model of cochlear implantation.

Dexamethasone administered prior to cochlear implantation has been shown to reduce the loss of residual hearing in experimental settings. However, its effect on the tissue response around the implant has not been extensively studied. In this study dexamethasone sodium phosphate was administered to guinea pigs via local delivery to the round window (2% dexamethasone for 120 min prior to surgery, 'local 2/120', or 20% dexamethasone for 30 min prior to surgery) or intravenously (2 mg/kg dexamethasone for 60 min) prior to implantation. Auditory brainstem responses (ABR) were monitored for 3 months, after which the cochleae were embedded in Spurr's resin and sectioned. The extent of the tissue response and the survival of the neurosensory structures were analysed. Both local 2/120 and systemically delivered dexamethasone improved ABR thresholds when compared with control animals. Systemic dexamethasone also reduced the tissue response around the electrode. This suggests that whilst both locally and systemically administered dexamethasone can protect residual hearing after cochlear implantation, their effects upon the tissue response to implantation may differ.