Risk factors for loss of ipsilateral residual hearing after hybrid cochlear implantation.

Cochlear implants (CIs) restore sound perception to individuals with severe to profound hearing loss by using electrical current to directly stimulate surviving auditory neurons. The S8 Hybrid CI, a 10mm long version of the original 24mm CI, was developed and validated in a recent FDA trial from 1999 to 20091,2. Shallow insertion of a shorter array at the base of the cochlea allows preservation of functional cochlear structures towards the apex. Thus with a hearing preservation CI, low-frequency or apical residual hearing is preserved, while the impaired high-frequency or basal regions are bypassed with electrical stimulation from the device. Patients with residual low-frequency hearing, common with age-related hearing loss (presbycusia), benefit from this device by using acoustic and electrical modes of hearing together. Ipsilateral post-implantation hearing loss has been described in every patient series of hearing preservation cochlear implantation. This hearing loss is generally mild ~12dB and coincident with implantation. Recently our group described a subset of these patients for whom hearing loss accelerates after activation, hypothesizing that high amplitude electric-acoustic stimulation (EAS) may cause excitotoxic damage to the peripheral afferent auditory system3. Here we analyze the same cohort of 85 patients from the FDA hearing preservation array multicenter trial and correlate ipsilateral post-implantation hearing loss with patient-specific medical risk factors known to be associated with presbycusia, such as age and the use of prescription medications. We also seek to assess the relative clinical significance of this post-implantation hearing loss for overall auditory function in hearing preservation CI recipients.