Protocol for CHIEF (cochlear implants and inner ear inflammation) study; an observational, cross-sectional, study of children and young people undergoing cochlear implantation
Authors: Hough Kate , Nichani Jaya , Findlay Callum , Bruce Iain A , Newman Tracey A 
Published: November 2024

Introduction

Cochlear implantation is a surgical treatment that restores hearing function. The implant uses a series of small electrodes to generate electrical currents in the cochlea. These currents simulate the auditory nerve to elicit hearing. Despite the success of this neuro-prosthesis, some people do not get the expected hearing benefit from their implant. One reason for this is that tissues in the cochlea vary in how they respond to the implantation of the electrode array. Many people have a healthy wound healing response that results in a mature scar tissue (fibrosis). However, some people have an altered, or heightened, inflammatory response associated with excessive fibrotic tissue growth in the cochlea. Evidence largely derived from pre-clinical studies shows that excessive tissue ensheathing the electrode array increases the electrical resistance of the current flow (impedance) and reduces the quality of electrical stimulation – both of which can lead to poorer hearing outcomes with the implant.

This study will add to our understanding of the people who have a heightened inflammatory response and more vigorous fibrosis (tissue growth) which can lead to poorer hearing outcomes. We propose that there are detectable individual inflammatory differences between people when they are implanted, which may result in variable hearing outcomes following implantation. If we could understand and identify the differences, we could detect people who may be at risk of less favourable outcomes and use targeted treatments, e.g., anti-inflammatories, to improve outcome.

Methods and analysis

An observational, cross-sectional, study of children and young people undergoing cochlear implantation. The study will take place at Manchester University Hospital NHS Foundation Trust (MFT) and the University of Southampton. Children and young people who meet the eligibility criteria for cochlear implantation at MFT will be invited to participate in the study. On the day of cochlear implant surgery, a sample of the middle ear mucous membrane, swabs of the nasopharynx and middle ear canal, cochlear fluid, and a blood sample will be collected. Samples will be analysed using a number of molecular techniques to determine the inflammatory status of the person at the time of implantation. Clinical hearing data will be collected for up to five years after implantation to explore the relationship between inflammation at time of implantation and long-term hearing outcomes.

Ethics and dissemination

This protocol has been ethically approved by IRAS (330110). Results will be submitted to international peer-reviewed journals and presented at international conferences. Results will be presented to a lay audience via our patient and public involvement and engagement group (ALL_EARS@UoS) website.

Article Summary

Strengths and limitations of the study

Strength: The first study that will provide the opportunity to characterise the immune state of the ear at the time of implantation and correlate it with hearing outcomes with a cochlear implant.

Strength: The surgical protocol and the participants routine clinical care will not be altered by being a study participant.

Strength: The first study to use spatial transcriptomics to characterise the gene expression of human middle ear macrophages in children undergoing cochlear implantation.

Limitation: This is an observational study. The results of this study will inform sample size and recruitment criteria for future interventional studies.

Limitation: Complete analysis and interpretation of the samples in this study requires several highly specialist and expensive techniques. This will require follow-on funding bids informed using the data from this work.