Objective: In recent years, otologists have begun to place cochlear implants into nonfunctioning ears after sudden unilateral hearing loss. Patients in these trials demonstrate differing degrees of hearing loss in the unimplanted ear. Few studies have examined the role of implantation in patients with normal hearing in the unimplanted ear. To understand if this practice benefits these patients in terms of tinnitus, sound localization, and speech understanding, the available world literature is reviewed.
Data sources: MEDLINE, Embase, and Cochrane databases were searched for publications from database inception to June 1, 2013, without restriction of language.
Study selection: A search of multiple medical databases was performed to identify articles reporting cases series of cochlear implantation for unilateral hearing loss. Subjects were included for analysis only if the course of hearing loss was acute and rapidly progressive, if the loss was severe to profound, and if the contralateral ear had normal hearing.
Data extraction and synthesis: Nine appropriate articles were identified, in which 36 patients met our inclusion criteria. Three meta-analyses were performed: of tinnitus (22 patients); of the lowest signal-to-noise ratio, which still allowed 50% sentence understanding (16 patients); and of sentence understanding at a fixed signal-to-noise ratio (12 patients). These found that measures of tinnitus reduction and decreased signal-to-noise ratios to still allow 50% speech discrimination were statistically significantly reduced. Systematic review of subjective changes of tinnitus in 27 patients, speech understanding in 16 patients, and sound localization in 16 patients found 96%, 100%, and 87% were improved, respectively.
Conclusion: Cochlear implantation in unilateral sudden hearing loss with a normal functioning contralateral ear might prove to be an effective therapy. Tinnitus is reduced as is the signal-to-noise ratio, which still allows 50% speech discrimination. All patients felt that they localized sound better, and most felt that they understood speech better. Further studies should be conducted to compare the success of hearing rehabilitation of cochlear rehabilitation and traditional modalities such as contralateral routing of signal and bone-anchored hearing aids.