8.1 Auditory implants for moderate to severe sensorineural hearing loss
To help patients with a sensorineural hearing loss, conventional air-conduction hearing aids are the first choice (e.g. behind-the-ear devices or BTEs; Figure 2.1, chapter 2). If the sensorineural hearing loss is not too severe, it is possible to make conversational speech audible with BTEs. However, speech recognition might still be troublesome, especially in noisy situations, despite the amplification. This is caused by the hearing-loss-associated impaired temporal-spectral processing of speech sounds in the cochlea (referred to as cochlear distortion; Plomp, 1978). Today’s digital devices make use of algorithms that enhance the speech sounds relative to the noise, like noise reduction algorithms and adaptive directionality of the BTE’s microphone (Dillon, 2012).
Note. In contrast to other chapters, references are listed at the end of this chapter
For patients with severe to very severe sensorineural hearing loss (> 70-80 dB HL), BTEs might no longer be sufficiently effective because proper restoration of the audibility of speech is not possible and because of severe cochlear distortion. Then, cochlear implantation becomes the next treatment option (Hoppe et al., 2015; Huinck et al., 2019), as elaborated in the next chapter, section 9.1. An alternative amplification option for patients with hearing loss below 70-80 dB HL is an (acoustic) auditory middle-ear implant (MEI, Verhaegen et al., 2008). High sound fidelity, high output with less feedback problems and the absence of an occluding earmold were claimed advantages of MEIs over BTEs (e.g. Goode, 1995). Since the late nineties, several different types of MEIs have been introduced for patients with sensorineural hearing loss (Snik, 2011). Nowadays (early 2021), two semi-implantable MEIs are on the market, viz. the Vibrant Soundbridge (VSB; Figure 2.6, chapter 2) and the Maxum device (Ototronix, USA; Pelosi et al., 2014). The latter device comprises a permanent magnet connected surgically to the stapes, in the middle ear. The driver is an electro-magnetic coil with electronics placed in a deep fitted in-the-ear hearingdevice. Early 2020, a competitor of the VSB, the semi-implantable Cochlear MET, was taken off the market.
In addition to semi-implantable MEIs, one fully implantable MEI is on the market, namely the Esteem device (Envoy Medical, St. Paul, MN, USA; Marzo et al., 2014). Another fully implantable MEI was the Cochlear Carina, which also was withdrawn from the market early 2020. Several systematic reviews have been published aiming at the claimed advantages of MEIs over BTEs. Pulcherio et al. (2014) concluded that, comparing the Carina and Esteem devices to BTEs, no structural audiological benefit was found. It should be noted that these implantable devices are 1. expensive and 2. involve (implant) surgery and 3. regularly, need revision surgery (every 5-10 years) to replace the battery; therefore, the cost-benefit ratio of these devices is highly unfavorable compared to BTEs. Another review by Kahue et al. (2014), comparing audiological outcomes obtained with the ( VSB and Maxum devices on the one hand and BTEs at the other, concluded that a surplus value of the MEIs could not be established. Since these reviews were published, while screening the more recent literature, just one more study was found with the Maxum as well as one with the Esteem device, published by manufacturer-independent research groups. Barbara et al. (2018b) reported on 3 patients using the Maxum; compared to BTEs, two patients had equal speech recognition scores and the third patient had a 10% higher word score with the Maxum. Regarding the Esteem device, Barbara et al (2018a) published an overview of their outcomes. The patient group described in this paper overlapped with that of a previous paper of the same authors, which was included in the above-mentioned systematic reviews by Kahue et al. and Pulcherio et al.
It might be concluded that compared to BTEs, today’s MEIs have no convincing audiological advantages and are expensive solutions. However, an exception was made for patients who don’t tolerate the earmold of BTEs owing to e.g. chronic external otitis, as formulated by Magnan et al., 2005 (consensus statements).The recent systematic reviews indicate that that statement remains valid. Edfelt et al. (2014) showed that for such patients the application of the VSB is cost effective! Note that according to the set-up of the Maxum, that device is not an option for patients with external otitis. No papers could be identified on the Esteem device, applied in patients with external otitis.
One manufacturer of MEIs acknowledges using their device only in patients with external otitis (VSB fact sheet, 2015).
In summary:
There is no evidence that MEIs for patients with sensorineural hearing loss led to better speech recognition than BTEs. However, the VSB might be used (cost-) effectively in patients with sensorineural hearing loss and chronic external otitis.
To help patients with sensorineural hearing loss and chronic external otitis, bone-conduction devices (‘BCDs’) have been applied as well. With a ‘BCD’, the ear canal remains open. Bone-conduction works but it is not really effective (see Chapter 2). Indeed, studies with the powerful percutaneous ‘BCD’ (Baha), applied in such patients showed that even with maximum amplification the result was insufficient (Snik et al., 1995). Stenfelt et al. (2000) came to a similar conclusion. More recent studies are lacking. In summary
To help patients with sensorineural hearing loss in need for amplification, studies showed that ‘BCDs’ have insufficient power
8.2 Capacity of VSB with today’s sound processors
In contrast to the Maxum and Envoy Esteem devices, the VSB has been widely applied. With the more recent sound processors (Amade or Samba for the VSB), improvements in sound quality have been achieved compared to the older processors. Concerning speech recognition, Figure 8.2 shows the %-correct score at normal conversational level (65 dB SPL) of 14 patients using these upgraded VSB processors. Patients with ski-slope audiograms were excluded, following Verhaegen et al., 2008. The drawn lines are taken from that latter study, based on the speech performance (phoneme score) of patients with previous-generation sound processors. The figure shows that the new data points are close to the line or somewhat better. Busch et al. (2016) reported a similar conclusion. As a reference, Verhaegen et al. showed that with a BTE, applied in patients with similar hearing loss, the mean speech score was significantly higher, e.g. at 65 dB HL the mean phoneme score was 90% with BTE versus 70% with VSB (see also the next chapter, section 9.1.2.
Figure 8.1. Speech recognition-in-quiet scores (presentation level 65 dB SPL; phoneme scores) as a function of the hearing loss of 14 VSB-Amade/Samba users (squares). The drawn line is the best fit from a previous study (Verhaegen et al., 2008).
A problem of using a MEI with an open ear canal, like the VSB, might be the interference between the MEI processed sound and the direct sounds. It should be noted that owing to the digital processing of audio processors, the amplified sounds are delayed, typically by 4 ms to 10 ms. That implies that the direct and processed sounds are not in phase for most frequencies, which might lead to a distorted sound. This phenomenon also occurs when fitting digital BTE devices with open earmolds (Groth & Sondergaard; 2004 and Stone et al., 2008). The latter study showed that the (annoying) interference depends on (and can be adjusted by) the gain level of the device and compression settings. Studies looking into this interference when using MEIs have not been published yet.
8.3 References chapter 8
Barbara M, Filippi C, Covelli E, Volpini L, Monini S. Ten years of active middle ear implantation for sensorineural hearing loss. Acta Otolaryngol. 2018a;138(9):807-814.
Barbara M, Volpini L, Filippi C, Atturo F, Monini S. A new semi-implantable middle ear implant for sensorineural hearing loss: three-years follow-up in a pilot patient’s group. Acta Otolaryngol. 2018b;138(1):31-35.
Busch S, Lenarz T, Maier H. Comparison of Alternative Coupling Methods of the Vibrant Soundbridge Floating Mass Transducer. Audiol Neurootol. 2016;21(6):347-355.
Carlsson PU, Håkansson BE. The bone-anchored hearing aid: reference quantities and functional gain. Ear Hear. 1997;18:34-41
Dillon H. Hearing aids. 2012, Thieme Verlag, Stuttgart, Germany
Edfelt L, Stromback K, Grendin J, et al., Evaluation of cost-utility in middle ear implantation in the ‘Nordic School’; a multicenter study in Sweden and Norway. Acta Otolaryngol. 2014;134:19-25
Goode RI. Current status and future of implantable electromagnetic hearing aids. Otolaryngol Clin N Am. 1995;28:141-146
Groth J, Sondergaard MB. Disturbance caused by varying propagation delays in non-occluding hearing aid fittings. Int J Audiol. 2004;43:594-599
Huinck WJ, Mylanus EAM, Snik AFM. Expanding unilateral cochlear implantation criteria for adults with bilateral acquired severe sensorineural hearing loss. Eur Arch Otorhinolaryngol. 2019;276(5):1313-1320.
Kahue CN, Carlson ML, Daugherty JA, Haynes DS, Glasscock ME 3rd. Middle ear implants for rehabilitation of sensorineural hearing loss: a systematic review of FDA approved devices. Otol Neurotol. 2014;35(7):1228-37.
Marzo SJ, Sappington JM, Shohet JA. The Envoy Esteem implantable hearing system. Otolaryngol Clin North Am. 2014;47(6):941-52.
Magnan J, Manrique M, Dillier N, Snik A, Hausler R. International consensus on middle ear implants. Acta Otolaryngol. 2005;125:920-921
Pelosi S, Carlson ML, Glasscock ME 3rd. Implantable hearing devices: the Ototronix MAXUM system. Otolaryngol Clin North Am. 2014;47(6):953-65.
Plomp R. Auditory handicap of hearing impairment and the limited benefit of hearing aids. J Acoust Soc Am. 1978;63:533-549
Pulcherio JO, Bittencourt AG, Burke PR, Monsanto R, de Brito R, Tsuji RK, Bento RF. Carina® and Esteem®: a systematic review of fully implantable hearing devices. PLoS One. 2014;17;9(10)
Rameh C, Meller R, Lavielle JP, Deveze A, Magnan J. Long-term patient satisfaction with different middle ear hearing implants in sensorineural loss. Otol Neurotol 2010;31:883-892
Snik A, Implantable hearing devices for conductive and sensorineural hearing impairment. In: F-G Zeng et al. (eds.) Auditory Prosthesis. New Horizons. Springer Handbook of Auditory Research 39, 2011:85-108
Snik AF, Mylanus EA, Cremers CW. Bone-anchored hearing aids in patients with sensorineural hearing loss and persistent otitis externa. Clin Otolaryngol Allied Sci. 1995;20:31-35
Stenfelt S, Håkansson B, Jönsson R, Granström G. A bone-anchored hearing aid for patients with pure sensorineural hearing impairment: a pilot study. Scand Audiol. 2000;29:175-185
Stone MA, Moore BCJ, Meisenbacher K, Derleth RP. Tolerable hearing aid delays. V. Estimation of limits for open canal fittings. Ear Hear. 2008;29:601-617
Verhaegen VJ, Mylanus EA, Cremers CW, Snik AF. Audiological application criteria for implantable hearing aid devices: a clinical experience at the Nijmegen ORL clinic. Laryngoscope. 2008;118(9):1645-1649
VSB fact sheet (VORP 503/Samba). Vibrant soundbridge System. Med-El website, downloads, 2015