**4. Therapeutic interventions for irreversible unilateral sensorineural hearing loss caused by ISSHL**

As mentioned earlier, patients with ISSHL have several hearing-related symptoms, which can be divided into four categories: hearing difficulty, disability of spatial hearing, discomfort, and tinnitus. Hearing difficulty includes several situations, such as conversation with several people and speech perception in noise. The efficacy of therapeutic interventions for patients with ISSHL needs to be evaluated against those four categories. The available methods for evaluating those four categories are summarized in **Table 1**.

The degree of unilateral hearing loss caused by ISSHL varies from mild to profound, and the selection of interventions depends on the degree of hearing loss. The interventions for ISSHL patients with severe-to-profound hearing loss can be considered the same as those for SSD patients, which include cochlear implant (CI), bone-anchored hearing aids (BAHAs), and contralateral routing of signals (CROS)


*SSQ, speech, spatial and qualities of hearing scale; APHAB, abbreviated profile of hearing aid benefit; GHABP, Glasgow hearing aid benefit profile; THI, tinnitus handicap inventory; VAS, visual analog scale.*

#### **Table 1.**

*Evaluation methods for four major problems in patients with ISSHL.*

hearing aid. If hearing loss is mild to moderate, a conventional air- conducted hearing aid may be the primary treatment. These treatments are described below.

#### **4.1 Therapeutic effects for patients with SSD**

The methods for evaluating the therapeutic effects of interventions for patients with SSD have generally included sound localization test, speech comprehension in noise, and subjective evaluation. The effects of the BAHA, CROS hearing aid, and CI interventions are summarized below.

#### *4.1.1 BAHA and CROS hearing aid*

The BAHA and CROS hearing aid have essentially the same characteristics in that a microphone is placed on the affected ear side and the sound is heard in the normal ear. Whereas a BAHA transmits sound via bone conduction, a CROS hearing aid transmits sound to a receiver on the normal ear by wireless or wired transmission. The therapeutic effect of these hearing aids can be summarized from the results of two systematic reviews for adult-acquired SSD [10, 11].

For sound localization by BAHAs, Kim et al. [10] reported that the percentage of correct sound localization was 13–65.8% before BAHA implantation and 15–68.5% after implantation, showing no significant difference in six studies. In a recent study, Agtrberg et al. [12] reported that BAHA neither improved nor deteriorated the localization abilities of patients with SSD. Kitterick et al. [11] reported that sound localization was not changed by CROS hearing aids in five studies and a significant deficit was indicated in one study. Therefore, it can be concluded that there is no improvement in sound localization with BAHAs or CROS hearing aids.

Speech comprehension in noise improves under certain conditions. Kim et al. [10] reported that in the situation of speech coming from the front and noise coming from the normal ear side, speech discrimination was statistically significantly improved after BAHA implantation in four out of six studies. Kitterick et al. [11] conducted a meta-analysis using data from the Hearing in Noise Test. A significant benefit was identified in the situation of speech coming from the front and noise coming from the normal ear side for both BAHAs and CROS hearing aids; however, a significant deficit was identified for both devices in the situation of noise coming from the affected ear side. The effects of BAHAs and CROS hearing aids are generally similar, with the former thought to be slightly superior. For the subjective evaluation of the benefits and adverse effects of the interventions, the abbreviated profile of hearing aid benefit (APHAB) and the Glasgow hearing aid benefit profile (GHABP) have been widely used. Kitterick et al. conducted a meta-analysis using data from the APHAB before and after the use of BAHAs and CROS hearing aids. Significant benefits of the BAHA were found for three subscales, reverberation, ease of communication, and background noise, but not for aversion to loud sound. Significant benefits of the CROS hearing aid were also found for two subscales: background noise and reverberation.

#### *4.1.2 Cochlear implant*

CI is a method of treating the deaf ear itself so that it can regain hearing ability. Therefore, the treatment concept is essentially different from the BAHA and CROS hearing aid. A study of CI for adult-acquired SSD was reviewed. Two systematic reviews [13, 14] and several subsequent reports [15–18] yielded similar results. These are summarized as follows.

**9**

**hearing loss**

*Associated Health Issues of Patients with Acquired Unilateral Hearing Loss*

statistically significant improvement following CI implantation.

For sound localization, Kitterick et al. [11] reported that only one of the three studies showed statistically significant improvement after CI surgery. Although most of studies reported improvement of sound localization after CI, a metaanalysis could not be conducted because of heterogeneous methodologies.

For speech comprehension in noise, Blasco and Redleaf [12] conducted a metaanalysis and reported in the situation where both speech and noise were coming from the front; the signal-to-noise ratio for speech perception in noise was significantly improved following CI. However, in the situation where speech was coming from the front and noise was coming from the affected side, no improvement was observed. For the subjective evaluation, Kitterick et al. [11] conducted a meta-analysis using data from the speech, spatial and qualities of hearing scale (SSQ ) [19]. They found significant improvement for all three subscales: speech, spatial, and "other"

For the subjective evaluation of severity of tinnitus, Blasco and Redleaf [13] conducted a meta-analysis using a visual analog scale from three studies and found

**4.2 Potential of interventions for ISSHL patients with severe-to-profound** 

BAHAs and CROS hearing aids improve hearing from the deaf side. Improvement in speech comprehension in noise can be expected when the speech comes from the deaf side or front and the noise comes from the normal ear side. However, the ability for sound localization cannot be expected, and it is not possible to restore spatial hearing function. Therefore, among the associated problems for patients with ISSHL with severe-to-profound hearing loss, both devices seem to

A CI improves speech comprehension in noise at least as well as the BAHA or CROS hearing aid. A CI also seems to have potential to improve sound localization, which could lead to restoration of spatial hearing ability. The SSQ subjective evaluation contains many assessment items related to spatial hearing [19], and the scores of spatial hearing were reported to improve after cochlear implantation. Although there have been no reports directly evaluating "hearing-related discomfort" as an important symptom of ISSHL, it may be improved if spatial hearing ability can be restored. Direct evaluation of this symptom is needed in future assessments. Patients with tinnitus can also be expected to experience improvement with a CI [13, 15, 18]. Overall, although further investigation is needed, a CI has the potential to improve speech comprehension in noise, spatial hearing, and tinnitus and may also improve discomfort. The indication of CI in patients with ISSHL is the confirmation of cochlear pathogenesis, and relatively early surgery after ISSHL onset should be considered [18].

**4.3 Potential of interventions for ISSHL patients with mild-to-moderate** 

Conventional hearing aids are indicated for ISSHL patients with unilateral mildto-moderate hearing loss. However, patients with mild-to-moderate hearing loss on

give no benefit for spatial hearing, discomfort, or tinnitus.

Overall, an important difference in the results of CI from those of the BAHA and CROS hearing aid is that there was a possibility of improvement for sound localization and spatial hearing ability. It is considered that these two factors are associated with each other. In addition, Legaris et al. reported that cortical reorganization and restoration of binaural function in the brain might be produced after 1 year of experience with CI in adult SSD patients by evaluation of cortical auditory evoked

*DOI: http://dx.doi.org/10.5772/intechopen.88200*

qualities.

potential changes [20].

**hearing loss**

#### *Associated Health Issues of Patients with Acquired Unilateral Hearing Loss DOI: http://dx.doi.org/10.5772/intechopen.88200*

*Advances in Rehabilitation of Hearing Loss*

**4.1 Therapeutic effects for patients with SSD**

CI interventions are summarized below.

*4.1.1 BAHA and CROS hearing aid*

CROS hearing aids.

background noise and reverberation.

These are summarized as follows.

*4.1.2 Cochlear implant*

hearing aid. If hearing loss is mild to moderate, a conventional air- conducted hearing aid may be the primary treatment. These treatments are described below.

The methods for evaluating the therapeutic effects of interventions for patients with SSD have generally included sound localization test, speech comprehension in noise, and subjective evaluation. The effects of the BAHA, CROS hearing aid, and

The BAHA and CROS hearing aid have essentially the same characteristics in that a microphone is placed on the affected ear side and the sound is heard in the normal ear. Whereas a BAHA transmits sound via bone conduction, a CROS hearing aid transmits sound to a receiver on the normal ear by wireless or wired transmission. The therapeutic effect of these hearing aids can be summarized from

For sound localization by BAHAs, Kim et al. [10] reported that the percentage of correct sound localization was 13–65.8% before BAHA implantation and 15–68.5% after implantation, showing no significant difference in six studies. In a recent study, Agtrberg et al. [12] reported that BAHA neither improved nor deteriorated the localization abilities of patients with SSD. Kitterick et al. [11] reported that sound localization was not changed by CROS hearing aids in five studies and a significant deficit was indicated in one study. Therefore, it can be concluded that there is no improvement in sound localization with BAHAs or

Speech comprehension in noise improves under certain conditions. Kim et al. [10] reported that in the situation of speech coming from the front and noise coming from the normal ear side, speech discrimination was statistically significantly improved after BAHA implantation in four out of six studies. Kitterick et al. [11] conducted a meta-analysis using data from the Hearing in Noise Test. A significant benefit was identified in the situation of speech coming from the front and noise coming from the normal ear side for both BAHAs and CROS hearing aids; however, a significant deficit was identified for both devices in the situation of noise coming from the affected ear side. The effects of BAHAs and CROS hearing aids are generally similar, with the former thought to be slightly superior. For the subjective evaluation of the benefits and adverse effects of the interventions, the abbreviated profile of hearing aid benefit (APHAB) and the Glasgow hearing aid benefit profile (GHABP) have been widely used. Kitterick et al. conducted a meta-analysis using data from the APHAB before and after the use of BAHAs and CROS hearing aids. Significant benefits of the BAHA were found for three subscales, reverberation, ease of communication, and background noise, but not for aversion to loud sound. Significant benefits of the CROS hearing aid were also found for two subscales:

CI is a method of treating the deaf ear itself so that it can regain hearing ability. Therefore, the treatment concept is essentially different from the BAHA and CROS hearing aid. A study of CI for adult-acquired SSD was reviewed. Two systematic reviews [13, 14] and several subsequent reports [15–18] yielded similar results.

the results of two systematic reviews for adult-acquired SSD [10, 11].

**8**

For sound localization, Kitterick et al. [11] reported that only one of the three studies showed statistically significant improvement after CI surgery. Although most of studies reported improvement of sound localization after CI, a metaanalysis could not be conducted because of heterogeneous methodologies.

For speech comprehension in noise, Blasco and Redleaf [12] conducted a metaanalysis and reported in the situation where both speech and noise were coming from the front; the signal-to-noise ratio for speech perception in noise was significantly improved following CI. However, in the situation where speech was coming from the front and noise was coming from the affected side, no improvement was observed.

For the subjective evaluation, Kitterick et al. [11] conducted a meta-analysis using data from the speech, spatial and qualities of hearing scale (SSQ ) [19]. They found significant improvement for all three subscales: speech, spatial, and "other" qualities.

For the subjective evaluation of severity of tinnitus, Blasco and Redleaf [13] conducted a meta-analysis using a visual analog scale from three studies and found statistically significant improvement following CI implantation.

Overall, an important difference in the results of CI from those of the BAHA and CROS hearing aid is that there was a possibility of improvement for sound localization and spatial hearing ability. It is considered that these two factors are associated with each other. In addition, Legaris et al. reported that cortical reorganization and restoration of binaural function in the brain might be produced after 1 year of experience with CI in adult SSD patients by evaluation of cortical auditory evoked potential changes [20].

### **4.2 Potential of interventions for ISSHL patients with severe-to-profound hearing loss**

BAHAs and CROS hearing aids improve hearing from the deaf side. Improvement in speech comprehension in noise can be expected when the speech comes from the deaf side or front and the noise comes from the normal ear side. However, the ability for sound localization cannot be expected, and it is not possible to restore spatial hearing function. Therefore, among the associated problems for patients with ISSHL with severe-to-profound hearing loss, both devices seem to give no benefit for spatial hearing, discomfort, or tinnitus.

A CI improves speech comprehension in noise at least as well as the BAHA or CROS hearing aid. A CI also seems to have potential to improve sound localization, which could lead to restoration of spatial hearing ability. The SSQ subjective evaluation contains many assessment items related to spatial hearing [19], and the scores of spatial hearing were reported to improve after cochlear implantation. Although there have been no reports directly evaluating "hearing-related discomfort" as an important symptom of ISSHL, it may be improved if spatial hearing ability can be restored. Direct evaluation of this symptom is needed in future assessments. Patients with tinnitus can also be expected to experience improvement with a CI [13, 15, 18]. Overall, although further investigation is needed, a CI has the potential to improve speech comprehension in noise, spatial hearing, and tinnitus and may also improve discomfort. The indication of CI in patients with ISSHL is the confirmation of cochlear pathogenesis, and relatively early surgery after ISSHL onset should be considered [18].

#### **4.3 Potential of interventions for ISSHL patients with mild-to-moderate hearing loss**

Conventional hearing aids are indicated for ISSHL patients with unilateral mildto-moderate hearing loss. However, patients with mild-to-moderate hearing loss on the affected ear and normal hearing on the opposite ear are less likely to realize the benefits of hearing aids on the affected ear and are often unable to wear them. Since some degree of auditory function remains in the affected ear, symptoms such as difficulty in hearing and impaired sound localization are milder than in patients with SSD, and, as a result, the beneficial effect of wearing a hearing aid seems to be difficult to perceive subjectively and to detect objectively. In addition, Kumpik et al. reviewed from several studies that horizontal localization by adult humans can adapt to varying degree to asymmetric hearing loss induced by occluding one ear [21]. Therefore, the abilities of sound localization and spatial hearing may be spontaneously restored in some degree in the patients with unilateral mild-to-moderate hearing loss. There do not seem to be any previous reports that examined the effect of hearing aids for hearing disability in patients with unilateral mild-to-moderate hearing loss.

Hearing-related discomfort is also common in ISSHL patients with unilateral moderate hearing loss, but the mechanism may differ from that in patients with unilateral severe-to-profound hearing loss. Patients with moderate hearing loss are more likely to have discomfort with sounds heard on the affected side, that is, increased loudness of noise caused by the recruitment phenomenon or distortion caused by the impairment of frequency selectivity function is unpleasant. Therefore, it is unlikely that a hearing aid will improve excessive loudness and distortion of sound.

On the other hand, tinnitus symptoms are more common in patients with mildto-moderate hearing loss due to ISSHL. Tinnitus retraining therapy using a hearing aid as a means of sound therapy has been widely conducted. At present, there is no high-quality evidence from systematic reviews [22], but improvement in the Tinnitus Handicap Inventory or visual analog scales has been widely recognized. In the future, it will be necessary to establish evidence of tinnitus improvement and to evaluate speech comprehension in noise and sound localization as well as hearingrelated discomfort in ISSHL patients with mild-to-moderate hearing loss.

## **5. Summary**

ISSHL is an important cause of persistent unilateral sensorineural hearing loss that affects thousands of new patients annually in Japan. The problems caused by ISSHL can be categorized into four factors: hearing difficulty, deterioration of spatial hearing, hearing-related discomfort, and tinnitus. The interventions that have been used to treat patients with unilateral hearing loss can be adapted to patients with ISSHL. The expected benefits of interventions for ISSHL patients are shown in **Table 2**. Although there are presently no treatments that provide satisfactory outcomes, CI is possibly the current most effective means of restoring some


*BAHA, bone-anchored hearing aid; CROS, contralateral routing of signals; CI, cochlear implant; HA, hearing aid;*  →*, not improved; ?, not available for applicable investigations.*

**11**

**Author details**

Kitasato University, Japan

provided the original work is properly cited.

Hajime Sano

*Associated Health Issues of Patients with Acquired Unilateral Hearing Loss*

The author has no conflict of interest to declare.

Department of Rehabilitation, School of Allied Health Sciences,

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

\*Address all correspondence to: sanohj@med.kitasato-u.ac.jp

of the lost binaural functions in patients with ISSHL who have severe-to-profound hearing loss. On the contrary, the effect of BAHA and CROS is quite restricted for

In the future, it will be necessary to unify evaluation methods for sound localization, speech comprehension in noise, and subjective questionnaires. Health-related QOL should be a component of the subjective assessments, and "hearing-related discomfort," which negatively impacts QOL for ISSHL patients, must be included as

*DOI: http://dx.doi.org/10.5772/intechopen.88200*

such patients.

a subjective evaluation item.

**Conflict of interest**

#### **Table 2.**

*Expected effect of interventions for patients with ISSHL.*

*Associated Health Issues of Patients with Acquired Unilateral Hearing Loss DOI: http://dx.doi.org/10.5772/intechopen.88200*

of the lost binaural functions in patients with ISSHL who have severe-to-profound hearing loss. On the contrary, the effect of BAHA and CROS is quite restricted for such patients.

In the future, it will be necessary to unify evaluation methods for sound localization, speech comprehension in noise, and subjective questionnaires. Health-related QOL should be a component of the subjective assessments, and "hearing-related discomfort," which negatively impacts QOL for ISSHL patients, must be included as a subjective evaluation item.
