Preserving hearing after CI is a notable accomplishment. Although current studies suggest that CI outcomes may not be improved by hearing preservation (unless there is aidable hearing, especially speech recognition), there is evidence that the electrical dynamic range is larger when some hearing is preserved, which could be advantageous.1 Current methods of preserving residual hearing after CI include surgical technique, electrode design and the use of pharmaceutical agents.
Ramos and colleagues2 of the University of Sᾶo Paulo recently described beneficial effects of the topical pharmaceutical hyaluronic acid in preserving low frequency residual hearing. The study was prospective, randomized, and controlled. Eighteen adult subjects (not electroacoustic candidates) were implanted with a Hybrid L24 electrode by a single surgeon. Preoperatively, all subjects received intravenous cefazolin and hydrocortisone (4 mg/kg). Group 1 (n=6) received no other intervention; Group 2 (n=6) also received intra-tympanic dexamethasone; and Group 3 (n=6) also received intra-tympanic dexamethasone plus hyaluronic acid application to the surface of the incised RWM.
Pre-op low frequency PTA (lfPTA; average threshold of 125, 250, 500 Hz) was compared to post-op lfPTA. Both Groups 1 and 2 lost approximately 30 dB. But Group 3, receiving hyaluronic acid, lost only 7 dB (p=0.002). The overall preservation of some residual hearing in the low frequencies was 88%. Also notable, intra-tympanic dexamethasone alone provided no additional benefit over pre-op intravenous steroids.
Hyaluronic acid just prior to electrode insertion appears to help preserve residual hearing. Hypothetical mechanisms may include reducing the escape of perilymph, ingress of blood or bone dust and frictional forces of insertion.
1. D’Elia A, Bartoli R, Giagnotti F, Quaranta N. The role of hearing preservation on electrical thresholds and speech performances in cochlear implantation. Otol Neurotol 2012;33:343–7.
2. Ramos BF, Tsuji RK, Bento RF…Brito R.Hearing preservation using topical dexamethasone alone and associated with hyaluronic acid in cochlear implantation. Acta Otolaryngol. 2015 May;135(5):473-7.