Toward the Future of Early Intervention for Adult Hearing Loss

Abstract

This issue of Seminars in Hearing has focused on the early intervention of adult sensorineural hearing loss (SNHL). Contributions to this monograph have taken a contemporary issues approach to the prevention, diagnosis, and treatment of mild SNHL. This article looks toward the future and discusses clinical and research implications for the early intervention of adult SNHL.

Learning Outcomes: As a result of this activity, the participant will be able to discuss the implications of the prevention, diagnosis, and early intervention of adult hearing loss.

This issue of Seminars in Hearing has focused on the early intervention of adult sensorineural hearing loss (SNHL). Although a quick glance at the title may cause some to think that the issue is about children with hearing loss, it is important that intervention of adult SNHL is initiated as early as possible if individuals are to avoid negative health-related quality of life (HRQoL) issues that may occur if this condition goes untreated. Audiologists may differ in their opinions as to whether patients with slight to mild SNHL (MSNHL) are even candidates for amplification, but perhaps, even more controversial is whether persons with hidden hearing loss (HHL) and/or cochlear synaptopathy (CS) could benefit from amplification. These issues are becoming increasingly relevant to researchers and clinicians everyday as greater numbers of persons are being identified with MSNHL and because investigations using animal models of hearing have demonstrated that early damage to the auditory system from noise or aging occurs long before hearing loss is diagnosed during routine audiologic evaluations. Basic and applied clinical researchers are feverishly working to develop test batteries and medical treatments that are aimed at diagnosing, treating, and preventing and/or reversing HHL and/or CS. Many patients who experience suprathreshold auditory dysfunction (e.g., difficulty understanding speech in noise and tinnitus) become frustrated when they and their families must deal with these auditory disorders, while their audiologists assess them with traditional audiometric tests and then counsel them that they have normal hearing according to the measures currently available. This scenario can be frustrating to audiologists as well when they believe their patients' complaints, but cannot validate their symptoms with current test procedures. The purpose of this article is to look toward the future and discuss clinical and research implications for the early intervention of adult SNHL.

Prevention

It is difficult to motivate individuals to use healthy hearing behaviors (e.g., use of hearing protection devices, HPDs) to reduce the impacts of occupational and nonoccupational noise exposure. In the case of occupational noise exposure, is it possible that the damage risk criteria leave too many workers at risk for HHL and/or CS? Are hearing health care providers who participate in hearing conservation programs lulled into a false sense of security when workers' annual audiograms show no standard threshold shifts? Could workers be developing HHL and/or CS even though they use HPDs correctly and consistently? At a more global level, do damage risk criteria need to be revisited and revised?

Individuals who manage hearing conservation efforts are challenged by adherence issues and must encourage those at risk for noise-induced hearing loss (NIHL) to practice healthy hearing behaviors. At least, employers can mandate the use of HPDs by their employees as part of a comprehensive hearing conservation program that includes education about NIHL. However, getting the general public to adhere to hearing conservation practices is considerably more difficult, especially with music and recreational enthusiasts who may not recognize the potential dangers of excessive noise. Now, and in the future, increased efforts at public educational outreach campaigns are needed to encourage individuals to avoid potentially damaging sounds at prolonged durations and to think about using HPDs when exposed to excessive nonoccupational and/or recreational noises. A great challenge to audiologists is to educate children and young adults about the dangers of excessive noise exposure, because it is difficult for them to make the connection between present noise exposure and its future impacts on their hearing and quality of life.

Several recent studies have investigated the development of HHL and/or CS in young adult musicians. Liberman and colleagues ¹ found that young adult musicians had summating potential-to-action potential ratios that were nearly twice that of their nonmusician peers. The young musicians also had significantly poorer speech recognition for words presented in noise and with temporal distortion (e.g., time compression and reverberation). It is important for young musicians to realize that the music they are exposed to during practices, performances, and at sporting events may potentially put them at risk for HHL and/or CS. Unfortunately, many collegiate musicians fail to practice healthy hearing behaviors even though they have been playing their instruments for 10 years or more, are music majors, and are dependent on their sense of hearing in their courses of study and future careers.

In this issue of Seminars in Hearing , Seever and colleagues ² assessed the effectiveness of the Adopt-A-Band program with members of the Pride of Oklahoma Marching Band at the University of Oklahoma. Research assistants, from the Hearing Evaluation, Rehabilitation, and Outcomes Laboratory, served as peer mentors and provided information to the band members about HHL and/or CS and discussed reasons why it is important for them to wear HPDs. They also provided demonstrations and practice with the proper insertion of musicians' earplugs. The Adopt-A-Band program was effective in changing band members' immediate concerns about and their intentions for preventing NIHL. However, it is unknown whether presentations such as these will result in band members' long-term adherence to practicing healthy hearing behaviors. Future research is needed to identify educational content that will motivate young musicians to avoid NIHL and HHL and/or CS.

In the future, it may be possible for persons routinely exposed to excessive noise levels to use pharmacotherapeutic agents and otoprotective compounds to prevent or reverse some NIHL. For example, preclinical studies using animal models of hearing have shown the effectiveness of antioxidants in protecting the cochlea against noise damage. Additionally, a group at Harvard Medical School has shown that delivery of neurotrophin-3 to the round window or its overexpression can help prevent and treat CS and NIHL in animal models. ^{3 4 5} However, translating successful interventions from preclinical animal studies to clinical use with humans will require the development of audiologic test batteries for HHL and/or CS for use in phase II clinical trials. At this point, CS can only be confirmed through histopathological studies. A test battery for HHL and/or CS is also needed for clinical audiologists who see patients who present to their clinics with complaints of “not being able to hear well,” “difficulty understanding speech in noise,” and/or tinnitus, yet present with pure-tone audiometric thresholds ≤ 20 dB HL from 0.25 to 8.0 kHz.

Diagnosis

In this issue of Seminars in Hearing , Barbee and colleagues ⁶ reported on a systematic review that they conducted on studies that used audiologic measures to assess HHL and/or CS in animal and human models of hearing to help in the development of a test battery. They found that the objective measures of auditory brainstem response (ABR) wave I amplitude and the summating potential-to-action potential ratio (SP/AP ratio) show promise for differentiating between individuals with excessive noise exposure histories but otherwise normal hearing from their nonexposed peers. A characteristic of systematic reviews is that they are often outdated soon after they are completed due to new studies being published all the time. In the short time since the completion of Barbee and colleagues' systematic review, Wojtczak and colleagues ⁷ showed that reduced acoustic reflex strength has been found in patients with noise-induced tinnitus but normal hearing and suspected CS when compared with peers without ringing in their ears. Although many studies have assessed the effectiveness of one or more audiologic tests for CS and/or HHL, others have taken a statistical approach to identifying possible HHL and/or CS. Ridley and colleagues' ⁸ multiple linear regression analysis revealed that certain measures of auditory function (i.e., ABR wave I and V amplitudes, SP/AP ratios, levels of distortion product otoacoustic emissions, and categorical loudness scaling) accounted for much of the variance in an outcome variable they called the threshold-in-noise residual (i.e., the residual of the correlation between thresholds in noise and thresholds in quiet), which can be used in determining HHL in humans with normal hearing and hearing loss. ⁹ Undoubtedly, a test battery for HHL and/or CS will be developed in the near future for clinical and research purposes. Additionally, self-assessment inventories and tests of suprathreshold auditory function such as speech recognition testing in noise likely will play an important role in identifying those with HHL and/or CS. ⁹

Early diagnosis of hearing loss in adults, including HHL and/or CS, will require educating health care providers about the negative impacts of auditory dysfunction on HRQoL and the possible benefits of amplification for these individuals. Primary care and other physicians need to know that patients' complaints of difficulty hearing, particularly in noise, and/or tinnitus should result in referrals to hearing health care professionals who should think beyond traditional audiometric results and who are informed about HHL and CS, and know that some patients with otherwise normal hearing may have suprathreshold auditory dysfunction. Clinicians should ask questions such as: (1) Do patients have an extensive history of exposure to excessive noise or other agents (e.g., ototoxic medications) that could place them at risk for HHL and/or CS? (2) Do patients need counseling regarding the importance of using HPDs? (3) Should patients' hearing sensitivity be monitored over time? (4) Are hearing aids appropriate for these individuals? (5) Should referrals be made to tinnitus specialists? Clearly, these patients are not fabricating their hearing difficulties and should not be dismissed simply because they present with normal audiometric results. Ideally, once identified and a baseline audiogram is established, these patients should be retested periodically because most patients with HHL and/or CS will likely go on to develop hearing losses that manifest on the standard audiogram and will eventually be candidates for amplification and/or hearing assistive technology. Hopefully, audiologists being proactive about patients' hearing complaints and alert to potential HHL and/or CS will allow clinicians to provide early diagnosis and treatments for losses that may progress later.

Treatment

In the future, patients with HHL and/or CS may be referred for treatment to repair cochlear ribbon synapses. Kujawa and Liberman ⁹ stated that spiral ganglion cells survive long after deafferentation occurs from noise exposure or aging, which creates a rather large therapeutic time window for treatment. Some pharmaceutical agents have been found to ameliorate the effects of CS caused by excessive noise exposure in animal models of hearing. Ideally, it will not be too far into the future until such pharmacotherapeutic agents are available to primary care physicians for the treatment of HHL and/or CS. Until that time, serial monitoring of hearing sensitivity, counseling on the importance of the use of healthy hearing behaviors, possible use of amplification or hearing assistive technology, and tinnitus management are possible avenues of intervention.

Roup ¹⁰ is conducting groundbreaking work in the fitting of mild-gain hearing aids on individuals who have normal audiometric hearing, but have significant difficulty hearing as indicated on the Hearing Handicap Inventory for Adults ¹¹ and/or surprisingly poor speech recognition in noise. The study's results have shown that fitting hearing aids that provide 5 to 10 dB of gain in the mid-to-high frequencies to amplify soft consonants resulted in a reduction of hearing handicap and an improvement in speech recognition in noise for these patients. Anecdotally, members of our own team have conducted trials with mild-gain advanced digital technology (ADT) hearing aids fit to a few patients having symptoms of HHL/CS and they have performed surprisingly well. These patients were generally young adult men and women whose major complaints were difficulty hearing in noise and tinnitus. They reported that they often had difficulty hearing family, friends, and coworkers, especially in groups and meetings. Most of them reported a history of early exposure to recreational shooting and/or military noise. However, when evaluated with a traditional test battery, they were frustrated to learn that their audiometric results indicated that their hearing was within normal limits. At the end of their trials with the hearing aids, they were unwilling to return the devices and reported that overall ease of listening was improved and that their tinnitus was less bothersome. We are in the process of evaluating these types of patients more formally, but these early results agree with those of Roup ¹⁰ and are encouraging that amplification might be a future benefit for patients having HHL/CS symptoms.

In this issue of Seminars in Hearing , Kimball and colleagues ¹² found that 67% of patients presenting to the Tinnitus and Sound Sensitivity Specialty Clinic in the John W. Keys Speech and Hearing Center (Allied Health Clinics) at the University of Oklahoma Health Sciences Center had slight-to-mild SNHL in addition to their tinnitus, although many of them thought that they had normal hearing. Because individuals with suspected HHL and/or CS often report tinnitus, patients who present to specialty and/or routine audiology clinics should be tested for suprathreshold auditory dysfunction even though their primary complaint is debilitating ringing in the ears. Kimball and colleagues ¹² found that degree of hearing loss and age were positively associated with the pursuit of amplification. Although possibly somewhat unique to their sample and clinic protocols, the more severe were their patients' tinnitus, the less likely they were to try hearing aids as a treatment, instead opting for use of smartphone applications. Presence of suprathreshold auditory dysfunction in addition to significant tinnitus might be an additional consideration when determining candidacy for hearing aids for those who present to clinics for tinnitus complaints, but who otherwise have normal hearing sensitivity.

Some individuals wait as long as 10 years from the time they first notice communication difficulties until they seek help. ¹³ It is unknown as to how many patients who initially present with HHL and/or CS will go on to develop measurable hearing loss, or how long it will take them to show up in our clinics. How do patients' auditory needs change during the development of measurable hearing loss? And, if patients' perceptual needs change during this process, what are the implications for the selection, evaluation, and fitting of hearing aids? In other words, initially, the primary complaints of patients with HHL and/or CS may be a lack of clarity and an inability to perceive the fine temporal details of speech, particularly in background noise along with tinnitus. In such cases, ADT hearing aids may be the best option for them, rather than simple mild-gain amplifiers (e.g., those that may be available as over-the-counter [OTC] in a direct-to-consumer [DTC] model). It is likely that ADT hearing aids fit through evidence-based practices ensuring the return of audibility may be the best options for patients with MSNHL. Johnson and colleagues ¹⁴ reported in this issue of Seminars in Hearing that patients with MSNHL wore their ADT hearing aids for 10 hours/per day and received significant benefit from and a high degree of satisfaction with their devices. It seems logical that if patients in the early stages of auditory pathology have positive experiences with amplification, then there may be an increase in future hearing aid uptake rates and use for those with SNHL, especially MSNHL.

In this issue of Seminars in Hearing , Jilla and colleagues ¹⁵ discussed the lack of accessibility to and affordability of hearing health care as it may affect hearing aid uptake and utilization. One of several potential solutions was provided through the Food and Drug Administration (FDA) Reauthorization Act of 2017, ¹⁶ which passed the 115th Congress in August 2017 and included the Over-the-Counter (OTC) Hearing Aid Act of 2017. This law calls for the FDA to create and regulate a new class of OTC hearing aids for patients with mild to moderate SNHL. The FDA was given a maximum of 3 years to explore and determine regulations for labeling, technical specifications, and manufacturer protections of OTC hearing aids made available through DTC models. The American Academy of Audiology ¹⁷ and the American Speech-Language-Hearing Association ¹⁸ published position statements generally supporting these efforts, but provided recommendations that those devices should only be for persons with MSNHL. Jilla and colleagues ¹⁹ sought to determine if there exists research to defend this recommendation and concluded that currently no evidence is available to support the use of OTC devices with persons having MSNHL. Moreover, they found that the few studies that have been conducted lacked the necessary external validity that would allow their results to be generalized to unserved and underserved populations and/or to devices that would be used in DTC scenarios. Although Humes and colleagues ²⁰ conducted a rigorous double-blinded, randomized clinical trial on the effects of delivery model on patient outcomes, over 80% of their participants had college degrees, were members of households at or above the middle class, and used premium ADT hearing aids that were fit with oversight of audiologists. In spite of the fact that their study was carefully controlled, its findings do not represent how devices will be delivered to consumers of OTC hearing aids in real-life DTC models that exclude hearing health care providers from the equation. Clearly, carefully controlled, true-to-life research is needed to direct future changes in clinical decision-making. These decisions should be based on the newest and best evidence that will support the importance of prevention and education, appropriate choices of clinical examinations that address hearing concerns beyond the pure-tone audiogram, and additional amplification options that will be forthcoming in the next few years (i.e., OTC hearing aids). The future of audiology will change and audiologists will need to reject the status quo and be prepared to entertain new clinical options to address NIHL, HHL, CS, tinnitus, MSNHL, and SNHL. Audiologists will have an important role in shaping the future of their profession and the ways in which their services are provided to those with hearing loss, especially MSNHL.