Combined electro-acoustic stimulation: a beneficial union?

The most pressing problem facing cochlear implant research is no longer making artificial hearing a reality. Instead, it is to develop devices that can more clearly reflect the capabilities of the human auditory system. Current cochlear implants rarely provide adequate pitch perception. As hearing loss commonly affects higher, more than lower frequencies, a possible solution is to preserve acoustic hearing at low frequencies by inserting a short electrode array and thus deliver combined electro-acoustic stimulation (EAS).

To determine whether individuals with severe-to-profound high-frequency hearing loss have realised this predicted benefit of combined EAS, over conventional cochlear implants, with respect to pitch.

A systematic review of publications pertaining to the benefits of combined EAS over conventional cochlear implantation, with specific reference to pitch perception.

A systematic literature search was conducted across multiple databases and supplemented by searching the reference lists of relevant trials and identified reviews.

The included studies suggest an overall benefit of combined EAS, over conventional cochlear implants, with respect to pitch. In addition, (i) 13% sustained a total loss of low-frequency hearing post-implantation of the short electrode array and, (ii) 24% had >20 dB hearing loss across all frequencies and/or total hearing loss.

For patients with severe-to-profound high-frequency hearing loss combined EAS appears to offer a significant, everyday, long-term benefit. However, further clinical trials with larger numbers of candidates are necessary to confirm this finding. The risks involved cannot be ignored, but there is potential for a variety of strategies to improve the safety margin.