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; their 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 a child with conductive or mixed hearing loss, sufficiently powerful amplification options should be advocated (see section 4.3).
The main purpose of (any) device fitting is optimising the audibility of speech (Amlani et al., 2002). A popular tool to assess the audibility of speech is the Speech Intelligibility Index (SII). SII is the proportion of normal speech that is audible to a patient with a specific hearing loss; the SII ranges from 0 to 100, zero means that normal speech is not audible and 100 means that the patient is able to fully hear normal speech. The SII is based on the idealised spectrum of conversational speech with a +/- 15 dB range, often referred to as the speech banana. The speech banana can be represented in the audiogram, see Figure 7.1. To calculate the SII, for each frequency band (1/3 octave wide), the proportion of speech in that band that is audible is weighted according to the contribution of that band to speech intelligibility (weighting factors indicated by the density of the dots in the figure). Next, these outcomes are summed for all 1/3 octave frequencies. In this simplified model, the speech banana 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 number of dots (max is 100 dots) is the SII; so, one dot counts for 1% of the ‘speech cues’. In the figure, post-intervention hearing thresholds are presented of two different interventions. Counting the dots shows that the SII is 90 and 22 for intervention 1 and 2, respectively. In their paper, Killion & Mueller (2010) also published a graph with the relationship between the SII and word recognition scores (their Figure 3). Using that graph, the SII of 90 and 22 matches with word recognition scores (WRS) of 95% and 20%, respectively. Evidently, treatment 1 is much more effective than treatment 2. The figure further suggests that when the maximum 15-dB-hearing-loss criterion of Northern & Downs is fulfilled, SII is 100, thus optimal.
Especially in children, hearing aid fitting should be bilaterally, as bilateral input leads to improved hearing in noise and might enable spatial hearing (see Chapter 6). Lately, statistics showed that children with bilateral compared to unilateral hearing devices developed better cognitive skills, which was caused by better perception of soft sounds and better speech perception in noisy places (de Raeve et al., 2015). The factor in between better hearing and better cognitive development is incidental learning. Most things that children learn are acquired in informal everyday situations.
Figure 7.1. Audiogram format with speech area according to Mueller and Killion (gray area). Post-intervention thresholds are shown of two different treatments, 1 (red line) and 2 (green line). The SII of the two interventions is determined by counting the dots above the hearing threshold (Source audiogram: Mueller and Killion, 1990).
Only approximately 1/3 of the knowledge of young children is acquired in structured quiet settings (e.g., in school). The remaining 2/3 is acquired during the day while playing, watching TV, talking with parents and other persons, etc. (de Raeve et al., 2015). Especially under these latter conditions, the children profit from bilateral hearing devices.
Probably, the observation that children with unilateral hearing loss (second ear normal) might display delayed educational development, has the same cause (Kuppler et al., 2013). This underlines that hearing with two ears is of utmost importance for the development of speech and language in children.
7.2 Literature review: why some interventions don’t work
Now, we will use the audibility of speech (thus the SII) 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 children involved, 3. with a unilaterally fitted device and 4. published after 2006. Most of the included studies addressed children with congenital conductive hearing loss.
Figure 7.2. Mean device-aided thresholds versus the sensorineural hearing loss component (SNHLc) of several study groups of children fitted with: percutaneous ’BCDs’ (red symbols, 5 studies*; summed 86 children), transcutaneous ‘BCDs’ (yellow symbols; 4 studies*; 130 children) and children with atresia repair (blue symbols, 3 studies*; 109 children). The black dots refer to three studies* in which the VSB was used (however, without a comparison with another device; 54 children).
* see note at the end of this chapter for references.
Figure 7.2 shows data obtained in children with conductive or mixed hearing loss. Concerning the percutaneous ‘BCD’ devices, evidently applied in pure condictive hearing loss (SNHLc was around 10 dB HL) overall, a mean device-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 for young children according to Northern & Downs (1991). Concerning the transcutaneous ’BCDs’, viz. the combined data of conventional ’BCDs’ (three studies, 49 children), ’BCDs’ on softband (two studies, 23 children) and the Sophono ‘BCD’ (one study, 15 children) a mean value of 29 dB HL was found. That value was expected, owing to the 10 to 15 dB poorer effectiveness of transcutaneous stimulation compared to percutaneous stimulation (Hakansson et al., 1984). Only one study was identified concerning the Sophono device with a mean device-aided hearing threshold of 33 dB HL (Denoyelle et al., 2015). That mean aided threshold was close to the reported threshold in the original paper, introducing the Sophono device (Siegert & Kanderske, 2013; reporting a mean value of 27 dB HL; 27 children).
With regard to surgical atresia repair, the mean long-term hearing threshold is 41 dB HL (three studies). That value is in good agreement with data from Nadaraja et al. (2013) who performed a systematic review of the literature. It should be noted that the outcomes of two interventions displayed in Figure 7.1 are Farnoosh et al.’s data (2014), with intervention 1 referring to a percutaneous ‘BCD’ application and 2 to atresia repair. The pre-intervention audiograms of the two groups were similar.
On the left side of the figure, the SII is presented calculated according to Killion and Mueller (2010). It is obvious that SII is the highest when using percutaneous ’BCDs’; ranging from 85 to 100 (corresponding WRS: 93 to 100%). Results with the transcutaneous ’BCDs’ are lower. Spread is larger and the SII ranges from subnormal (75; WRS of 90%) to moderate(50; WRS of 70%). Children with such a low SII might be prone to developmental delays. The SII after reconstructive surgery is particularly low, below 50. Indeed, Evans & Kazahaya (2007) reported that 90% of their operated children still needed some kind 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 that presented results compared to another amplification device. However, three studies on VSB application in children with conductive loss were identified with at least 10 children involved. The mean aided thresholds of these three studies with VSB users are presented in Figure 7.1 as black dots. These data are in the same range as those of the transcutaneous ’BCDs’ what is somewhat disappointing and might be described to the experimental character of these studies. More data are needed (see update 2020, new section 7.2.1). So far, the ‘Bonebridge’ has hardly been applied in children (Sprinzl & Wolf-Magele, 2015) and is not further considered here (see update 2020, new section 7.2.1).
Children with acquired conductive or mixed hearing loss because of chronic inflammation will benefit from amplification in the same way as children with congenital conductive hearing loss. Mostly, for this indication, BTEs are contraindicated for medical reasons.
Figure 7.2 presents data that can be used for counselling parents of children with conductive hearing loss. In short:
Reconstructive surgery in case of congenital atresia of the ear canal is, on the average, the least effective treatment.
For children with predominantly conductive hearing loss, today’s percutaneous ’BCDs’ provide more adequate gain than transcutaneous ’BCDs’, what might enable a better spontaneous development.
7.2.1 Update of Figure 7.2 using data published between 2016 and 2020
Update of the data presented in figure 7.2 is based on an additional search of the literature; search period: 2016 (end previous search period) until early 2020. For details of the selection process, see note at the end of this chapter. Seven additional studies were identified, describing 11 groups of persons with different treatments. Data of the latest evaluation moment were used. The table below presents all the data averaged (viz. the mean post-intervention thresholds and the mean bone-conduction thresholds (more precisely, the mean threshold at 0.5, 1, 2, 4 kHz of each study was used to calculate the average over studies) per type of treatment, including the data of the previous search (presented in Figure 7.2). Table 7.1 shows that the mean bone-conduction threshold (column 3) per type of treatment is rather comparable. The mean post-intervention thresholds (next column) varied between 20 dB HL and 41 dB HL.
Using all the studies (from the previous and new literature search) that presented frequency-specific post-intervention thresholds, the mean post-intervention threshold was calculated per frequency and per type of intervention to enable calculating the SII and the associated word recognition score (WRS). The last column of the table presenting the WRS, suggests once more that these treatments are not equivalents. As concluded before, especially, the outcomes of surgical atresia repair are disappointing followed by the passive transcutaneous ‘BCD’s. The results obtained with the ‘Bonebridge’ and percutaneous ‘BCD’ are the best.
The data in the table should be considered with some caution: regarding the Sophono device and the VSB, 2 and 4 studies, respectively, were identified.
Table 7.1
| Treatment
|
studies | Subjects,
cumulative |
Mean bc
threshold |
Mean post intervention threshold with (range) | Estimated WRS; % correct |
| Atresia repair | 5 | 199 | 11 dBHL | 41 (33-47) dBHL | 25% |
| Percut. ‘BCD’ | 6 | 135 | 11 | 20 (15-22) | 95 |
| ‘Bonebridge’ | 7 | 100 | 10 | 27 (19-31) | 90 |
| Sophono | 2 | 42 | 16 | 35 (35/36) | 65 |
| Conv. ‘BCD’ | 8 | 126 | 11 | 33 (27-45) | 70 |
| VSB | 4 | 60 | 11 | 31 (27-40) | 75 |
Percut. stands for percutaneous; conv. for conventional ‘BCD’, including ‘BCD’ on softband; bc for bone conduction; WRS for word recognition score
7.3 Age at intervention and implant stability in children
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. A transcutaneous ‘BCD’ with softband can be used in all the other cases. It is easier to use and thus better accepted than a steel headband (Hol et al., 2005). The position of the stimulating bone-vibrator over the skull can easily be changed. The ‘BCD’-aided thresholds with such devices typically lay between 25 dB HL and 30 dB HL (e.g., Verhagen et al., 2008; Denoyelle et al., 2015), which might be acceptable but only for learning speech at a basal level (Northern & Downs, 1991; Verhagen et al., 2008). Therefore, replacement of a ‘BCD’ on head/softband by a percutaneous ‘BCD’ or other more powerful solutions should remain on the agenda and, meanwhile, speech and language development should be monitored.
The use of percutaneous ’BCDs’ implies implantation of a skin-penetrating titanium implant, anchored in the skull, behind the ear. Concerning the youngest age at which such implantation is feasible, the thickness of the skull plays an important role. At least 3 mm is preferred (Snik et al., 2005). This implies that the child must be approximately 4 years old; nevertheless, even then, the loss of these implants is approx. 3 times higher than in adults (e.g., Dun et al., 2010). McDermott et al. (2009) reported that implant loss was high amongst the under fives and much less in older children. Other studies didn’t find such a distinct dependence of implant loss on age at implantation (de Wolf et al., 2008).
The subcutaneous magnet, for the coupling of a Sophono or Baha Attract processor, can be implanted from age 5 onwards, according to the manufacturers. Bezdjian et al. reviewed the literature and found 3 serious adverse reactions in 99 patients using the Sophono device, mainly children (Bezdjian et al., 2017). Dimitriadis et al. (2016, 2017) reported that the complication rate with the Baha Attract was low, when compared to the percutaneous ‘BCD’.
VSB with the transducer placed in the ‘round-window’ niche of the cochlea has been applied in children as young as 2 months (Mandala et al., 2011). However, since 2011, little has been published. Only one paper was found (with at least 5 implanted children); Leinung et al. (2017) presented results obtained in 13 young children with atresia of the ear canal. Age at implantation varied from 1.3 to 4.2 years with an average of 2.5 years. While the mean bone-conduction threshold (at 0.5, 1, 2, 4 kHz) of the whole group was 8 dB HL, the mean device-aided threshold was 40 dB HL, which is poor compared to the data presented in Table 7.1. In order to advocate VSB implantation in toddlers and young children, more evidence is needed.
The preferred age at intervention for reconstructive surgery (atresia repair) is 5-6 years and, furthermore, only relatively mild atresia-cases should be considered for surgery (e.g., Declau et al., 1999). Concerning stability, revision surgery might be necessary, up to one-third of the cases, as reported by Farnoosh et al. (2014). These authors compared atresia repair with percutaneous ‘BCD’ application, amongst other, with respect to medical complications. Percentage of revision surgery after atresia repair was almost 3 times higher than that after ‘BCD’ implantation. Therefore, it was suggested that, also in terms of medical aftercare, percutaneous ’BCDs’ might be a better choice than atresia repair.
7.4 Percutaneous or transcutaneous ’BCDs’ in children, counselling issues
When a child is approx. 4 years old, the conventional ‘BCD’ should be ‘upgraded’. Parents might choose for transcutaneous ‘BCD’ instead of percutaneous ‘BCD’, because of stability issues, daily care of the skin around the skin-penetrating-implant and/or emotional problems to accept titanium implants sticking out, through the skin. Then the remaining amplification options are to use either the Sophono device (Alpha 2 MPO) or the Baha Attract, applicable from age 4 or 5 years. First data showed that, as expected, the Baha Attract is as effective as Baha on a Softband (Kurz et al., 2014). Nowadays, as a sound processor, the Baha 5 power is advocated, which is more powerful than the standard Baha. The use of the Baha power processor will improve the MPO by several dBs. When bilateral transcutaneous ‘BCDs’ are used, in predominant conductive hearing loss, aided thresholds are expected between 25 dB HL and 35 dB HL, with corresponding SII values between 85 and 50 (corresponding WRS: 93% and 70%). This might be just safe but suggests that these children should be followed-up more closely than bilateral percutaneous ‘BCD’ users concerning their speech and language development. It still remains of importance to keep a change to a percutaneous ‘BCD’ on the agenda.
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, can only be used effectively in structured situations like classrooms.
*Note. References belonging to the studies summarised 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. The update of figure 7.2 (early 2020) was based on an additional literature search using Pubmed. The search string comprised the words: children, hearing, thresholds, and either a device name (Baha, Ponto, Bonebridge, Sophono, Vibrant Soundbridge) or atresia, surgery. Studies were excluded if aiming at subjects with just unilateral hearing loss, single-sided deafness or sensorineural hearing loss. The inclusion criteria used were: 1. either the aided PTA4 or the aided thresholds at 0.5, 1, 2, 4 kHz should have been reported, as well as bone-conduction thresholds and 2. group size should be more than 9. The newly identified studies comprised: Zhao et al., 2016; Fan et al., 2019, Bravo-Torres et al., 2018, Kulasegarah et al., 2018, Ren et al., 2019, Ahn et al., 2018, Zernotti et al., 2019, Ratuszniak et al., 2019.