Unilateral versus simultaneous bilateral cochlear implantation in adults : a randomized controlled trial

Abstract

Worldwide, more than 550 million people suffer from disabling hearing loss (≥35dB in the better ear). More than 60 million suffer from severe hearing loss or worse (≥61dB). The most common type of hearing loss is sensorineural hearing loss, caused by a defect inside the cochlea. Hearing aids are usually the first treatment option. In case of a severe hearing impairment, hearing aids may be inadequate and cochlear implants may be considered. A cochlear implant is a device that can receive sound, process, transmit and convert it into electrical signals, and present it to the brain by direct stimulation of the auditory nerve. This is possible thanks to an electrode array that is surgically inserted into the cochlea. Cochlear implantation (CI) has proven to be very successful. It enables deaf people to hear again. In the Netherlands, adult patients eligible for CI, normally receive reimbursement for one cochlear implant only. Cochlear implantees are, overall, deaf in both ears and after receiving a cochlear implant, they still have a significant hearing impairment. It is well known that people with only one functioning ear find it difficult to understand speech in noise and to determine which direction sounds come from. Several studies have shown that bilateral CI (BiCI) may be beneficial in these difficult listening situations. However, Zorginstituut Nederland (ZiNL), decided that the quality of these studies, investigating the benefits of BiCI compared with unilateral CI (UCI), is too low to justify reimbursement of BiCI in adults. In order to properly investigate the benefits and cost-utility of BiCI compared with UCI in adults with a severe postlingual hearing loss, we started a multicenter, randomized controlled trial in 2010. Thirty-eight patients were included in this study. Nineteen patients received two cochlear implants simultaneously. The other 19 first received one cochlear implant and a second implant 2 years later. To adequately test the participants’ spatial listening capabilities, we used the Dutch version of the AB-York crescent of sound. The primary outcome measure of our study was speech understanding in noise, with speech and noise coming from straight ahead, measured with the U-STARR (Utrecht Sentence Test At Randomized Roving levels). This test is explained and validated in this thesis. The main outcomes of our research are: 1. That simultaneous BiCI compared with UCI is effective, and 2. That BiCI is cost-effective compared with the Dutch generally accepted willingness to pay. We also performed a review study to analyze what the effect of time between sequential implantations is on hearing performance. We show that a second implant can be beneficial even with a substantial interval between implantations, although the quality of the evidence was rather poor.