- 7.1 Introduction; children should not be treated as young adults
- 7.1.1 Audibility of speech; a useful and simple way to assess audibility
- 7.2 Literature review: why some interventions are not effective
- 7.3 Age at intervention and stability
- 7.4 Percutaneous or transcutaneous BCDs in children, counselling issues
7. Challenges in children; critical choices
7.1 Introduction; children should not be treated as young adults
Counselling adults, who according to their audiogram should profit from amplification, is not always successful. Adults might deny their hearing problems or postpone a hearing aid trial. If their attitude is more positive, they might only be interested in hardly visible devices, even if speech recognition with such devices is not optimal.
For children, there is less room to move because the better the hearing the higher the chance that the child will develop normally. According to Northern and Downs (1991; referred to in chapter 1), indeed, children need (sub)normal hearing (15 dB HL or less) to ensure normal development of speech and language. Therefore, when counselling the parents of any child with conductive or mixed hearing loss, only sufficiently powerful amplification options should be advocated (paragraph 4.3).
7.1.1 Audibility of speech; a useful and simple way to assess audibility
The central issue during (any) device fitting is audibility (Amlani et al., 2002). A popular tool to assess audibility is the Audibility Index (AI), or, related, the Speech Intelligibility Index (SII). AI predicts the proportion of normal speech that is audible to a patient with a specific (aided or unaided) hearing loss. The AI can range from 0 to 100, zero means that normal speech is not audible and 100 means that the patient is able to hear normal speech completely.
In short, the AI is based on the idealized spectrum of conversational speech with a +/- 15 dB range, see Figure 7.1. To calculate the AI, for each frequency band, the proportion of speech in that band that is audible is weighted according to the contribution of that band to speech intelligibility. In the simplified model presented in the figure, the speech area stretches from 20 dB HL up to 50 dB HL, over a frequency range of 250 to 6000 Hz (Mueller and Killion, 1990; Killion and Mueller, 2010). The density of dots (in total 100 dots) refers to the weighting factors.
In Figure 7.1, aided hearing thresholds are presented, comparing two different interventions. Counting the dots, following the procedure described by Mueller and Killion, shows that the AI is 90 and 22 for intervention 1 and 2, respectively. Word recognition scores are directly related to the AI; using the data presented by Mueller and Killion, the corresponding word scores are 95% and 25%. Figure 7.1 further shows that if the no-more-then-15-dB hearing loss criterion, formulated by Northern & Downs is fulfilled, AI will be optimal.
Especially in children, fitting of hearing devices should be bilaterally as bilateral input leads to improved hearing in general and it enables spatial hearing (Dun et al., 2013). Consequently, speech recognition over-a-distance improves as well as speech recognition in noisy places. Lately, it has been shown that deaf children with bilateral devices compared to those with a unilateral device (CI) developed better cognitive skills. Statistics showed that this improvement could fully be ascribed to better perception of soft sounds and better speech perception in noisy places (de Raeve et al., 2015). The suggested factor in between better hearing and better cognitive development was incidental learning.
Figure 7.1. Audiogram format with speech area according to Mueller and Killion (gray area). Aided thresholds are shown of two interventions, 1 (red line; Baha application) and 2 (green line; atresia repair). The Audibility Index (AI) of the two interventions can be easily determined by counting the dots above the hearing threshold (Source: Mueller and Killion, 1990). The data points of the two interventions were taken from Farnoosh et al. (2014).
Approximately 1/3 of a child’s knowledge is acquired in structured settings, the rest while playing, watching TV, talking with parents and other persons, etc. (de Raeve et al., 2015). Under these latter conditions, the children profit from bilateral devices.
The observation that children with unilateral hearing loss (second ear normal) have delayed educational development has, most probably, the same cause. Such children don’t profit optimally from incidental learning, owing to impaired hearing abilities in unstructured situations (Kuppler et al., 2013). This underlines that hearing with two ears is of utmost importance for children developing their abilities.
7.2 Literature review: why some interventions are not effective
Let us use the audibility concept to find the best intervention for a child with congenital conductive or mixed hearing loss. A literature search was carried out with as search terms: children, conductive hearing loss, mixed hearing loss, and (Baha or Ponto or Sophono or softband or Vibrant Soundbridge or surgery or conventional bone conduction or Bonebridge). Next, those papers were selected in which 1) two interventions were compared, 2) with at least 10 patients, 3) published between 2006 and early 2016. Almost all included studies addressed children; two studies also included some adults.
Figure 7.2. Mean aided thresholds versus the sensorineural hearing loss component (SNHLc) of several groups of children fitted with: percutaneous BCDs (red symbols, 5 studies*; summed 86 children), transcutaneous BCDs (yellow symbols; 5 studies*; 142 children) and children with atresia repair (blue diamonds, 3 studies*; 109 children). The bleu dots refer to 4 studies* with VSB (without a reference device; 64 children). One study* with the Bonebridge was traced (black triangle, 12 children). The dotted black line presents the target thresholds, according to paragraph 4.3, website www.snikimplants.nl.
* see note at the end of the chapter for the references
Figure 7.2 shows the data. Concerning percutaneous BCD devices, overall a mean aided threshold of 19 dB HL was found. That is close to the value that is mentioned in the ‘Practise Guidelines’ for fitting percutaneous devices (17.5 dB HL; Roman et al., 2011) and the 15 dB HL, which is the upper limit for a handicapping hearing loss according to Northern & Downs (1991). Concerning the transcutaneous BCDs, combined data of conventional BCDs (3 studies, 49 children), BCDs on softband (2 studies, 23 children) and the Sophono BCD (2 studies, 21 subjects) show a mean of 29 dB HL. Such a mean value is expected, owing to the 10-15 dB worse effectiveness of transcutaneous stimulation compared to percutaneous stimulation (Hakansson et al., 1984). The mean aided hearing threshold of the 2 studies concerning the Sophono device was 32 dB HL. This mean aided threshold is comparable to that reported in the original paper introducing the Sophono device (Siegert & Kanderske, 2013; mean of 27 dB HL; 27 patients).
With regard to atresia repair, the mean long-term hearing threshold is 41 dB HL (3 studies) with a mean remaining air-bone gap of 30 dB. That latter value is in good agreement with data from Nadaraja et al. (2013); they showed in their systematic review paper that one year after surgery, almost 50% of operated atresia patients (children and adults) had a remaining air-bone gap of 30 dB or more.
On the left side of the figure, the Audibility Index is presented calculated according to Mueller and Killion (1990), assuming a ‘flat SNHLc’ (not unusual for predominantly conductive hearing loss). It is obvious that audibility is the highest when using percutaneous BCDs, with AI ranging from 85 to 100. Results with the transcutaneous BCDs are lower. Spread is larger and audibility ranges from subnormal to insufficient; (AI ranging from 50 to 75). Children with such low AI values might be prone to developmental delays. The AI after reconstructive surgery is too low, below 50. Indeed, Evans & Kazahaya (2007) reported that 90% of their operated children still needed some form of amplification after atresia repair.
Concerning the use of the VSB with its actuator coupled to one of the cochlear windows, no studies were found yet that presented results compared with another device, in (at least 10) children. However, 4 studies on VSB application in children with predominantly conductive loss were identified with at least 10 children involved. The mean aided thresholds of these studies are presented in Figure 7.2 as blue dots. One study was identified using the Bonebridge in (12) children. These data (VSB and Bonebridge) are in the same range as those of the transcutaneous BCDs what is less than expected and might be described to the experimental character of these applications. More data are needed.
Figure 7.2 shows that 7 studies had a mean result close to or better than the target line (broken blue line). It is generally acknowledged that children might need more amplification than adults, for proper communication (e.g. Dillon 2012, chapter 16).
The figure presents data that can be used as a starting point for counselling parents of children with conductive or mixed hearing loss. In short:
Reconstructive surgery in case of congenital aural atresia is, on the average, not an effective treatment for children. For children with predominantly conductive hearing loss, today’s percutaneous BCDs are better than transcutaneous BCDs, enabling a better spontaneous development. While fitting such devices, focus should be on audibility.
7.3 Age at intervention and stability
After neonatal hearing screening and a diagnosed bilateral conductive hearing loss few amplification options are available. When the tympanic membrane is visible, BTEs might be used. In all other cases, a transcutaneous BCD with headband or softband can be used. In neonates, mostly a BCD with softband is chosen. It is easier to use and thus better accepted than a steel headband (Hol et al., 2005). The position of stimulating bone-vibrator over the skull can be changed. Aided sound field thresholds with such devices typically lay between 25 and 30 dB HL (Verhagen et al., 2008; Denoyelle et al., 2015), which seems to be just acceptable for basal language learning only (Verhagen et al., 2008). Therefore, in young children, replacement of a BCD on head/softband by a percutaneous BCD or another powerful solution should remain on the agenda and, meanwhile, it is wise to monitor the speech and language development.
The use of percutaneous BCDs involves implantation of a skin penetrating titanium coupling (see Figure 7.3). Concerning the youngest age at which such implantation is feasible, thickness of the skull plays an important role: 3 mm or more is preferred (Snik et al., 2005). This implies that the child must be approximately 4 years old. Nevertheless, the loss of implants in children, in relation to follow-up, is 3 times higher than in adults (e.g. Dun et al., 2010). Children, as young as 2 years, have been implanted mostly with varying rates of success. McDermott et al., (2009) reported that implant loss was high amongst the under fives (40% of the implanted children lost an implant), much less in older children and at adult levels for children over 10 years (1% loss). Other studies didn’t find such a strong dependence of implant loss on age at implantation (de Wolf et al., 2008). Recently, improved titanium implants have been brought to the market with, in adults, a significantly better stability (see paragraph 5.1.2). Whether or not these implants also lead to better stability in children is in debate (Den Besten et al., 2015).
The Sophono magnetic coupling can be used from age 5, according to the company. Little has been published on stability; only some short-term problems have been described (e.g. Denoyelle et al., 2015). VSB with the transducer placed in the round window niche has been applied in children as young as 2 months (Mandala et al., 2011). However, the experience in young children is still limited, thus it seems to be too early to advocate VSB implantation in toddlers. However, this seems to be a promising option.
The preferred age at intervention for reconstructive surgery (atresia repair) is 5-6 years and only relatively mild cases should be considered (e.g. Declau et al., 1999). Concerning stability, revision surgery might be necessary in up to one-third of the cases as reported by Farnoosh et al. (2014). These authors compared atresia repair with percutaneous BCD application, amongst others, with respect to medical complications. Percentage of revision surgery after atresia repair was almost 3 times higher than that after percutaneous BCD surgery. So, also in terms of medical aftercare, percutaneous BCDs seem to be a better choice than atresia repair.
7.4 Percutaneous or transcutaneous BCDs in children, counselling issues
Parents might choose for transcutaneous BCD instead of percutaneous BCD, because of stability issues, daily care of the skin around the penetrating implant and/or emotional problems to accept titanium implants sticking out, through the skin. Then the amplification options that remain are to use either the Sophono device or the Baha Attract (see Figure 7.3), applicable from age 4 or 5 years. The latter option is rather new. First data showed that, as expected, the Baha Attract is as effective as Baha on Softband (Kurz et al., 2014). Nowadays, as sound processor, the Baha BP110 is advocated, which is more powerful than the standard BP100 or BP4. The use of the BP110 will improve the MPO by several dBs. When bilateral application is being used, in predominant conductive hearing loss, aided thresholds are expected to lie between 20 and 25 dB HL, with corresponding AI between 100 and 80. This seems safe but it has been suggested that these children should be followed-up more closely than percutaneous BCD users concerning their speech and language development. It remains of importance to keep a change to a percutaneous BCD on the agenda.
Figure 7.3. Left-side pictures concern the wee-known percutaneous Baha device, the ones in the middle, the Sophono Alpha device and the right-side pictures presents the Baha Attract. Source: the internet
Another suggestion that has been put forward to further support children with transcutaneous BCDs, is the provision of an additional personal FM system. Those systems, coupled to the child’s BCD, might enable better speech recognition, however, mainly in structured situations like class rooms. Their benefit is in debate with respect to incidental learning. In other words, choosing powerful amplification options (percutaneous BCDs) remains of high importance. Then gain and MPO might improve by 10 to 15 dB. Concerning the stability issue, no conclusive data have been published yet on the stability of the new transcutaneous BCDs.
Sylvester et al. (2013) showed that if the hearing loss is of the mixed type, even when the SNHLc is just 25 dB HL, the Sophono device (Alpha 1) is ineffective. Studies using the Baha Attract in such cases are still missing. In mixed hearing loss it is probably always better to choose for percutaneous BCDs, and if the SNHLc is advanced, additional personal FM systems might be very helpful.
*Note. References belonging to the studies summarized in Figure 7.2: Claros & Pujol, 2013; Frenzel et al., 2015; Verhagen et al., 2008; Farnoosh et al., 2014; Ricci et al., 2011; Denoyelle et al., 2015; Bouhabel et al., 2012; Evans & Kazahaya, 2007; Christensen et al., 2010; Mandala et al., 2011; Powel et al., 2015; Roman et al., 2012; Baumgartner et al., 2016.