I ncreasingly, experts are recognizing that the expansion of cochlear implant candidacy could improve outcomes for a larger population of patients with hearing loss, including those who have better speech-recognition abilities or single-sided deafness.
For 30 years, cochlear implantation has served as an accepted treatment for profound, bilateral sensorineural hearing loss. Over time, the criteria for cochlear implant candidacy have become more lenient, allowing more and more patients to benefit from the technology.
When the first cochlear implant was approved by the U.S. Food and Drug Administration (FDA) in 1984, only adults were considered suitable candidates. Five years later, children 2 years of age and older became eligible. Then in 2000, the FDA lowered the cochlear implant threshold to 12 months of age. Many babies younger than 12 months have been implanted off protocol.
“Today, there are modified cochlear implants that are indicated for patients with substantial low-frequency residual hearing and severe-to-profound high-frequency hearing loss,” said Margaret Dillon, AuD, assistant professor in the Department of Otolaryngology/Head and Neck Surgery at the University of North Carolina School of Medicine. “Despite these advancements, research has shown that current candidacy criteria continue to limit access for patients who could benefit from cochlear implantation.”
Approximately 324,200 people worldwide had gotten cochlear implants as of December 2012, according to the FDA. In the United States, about 58,000 adults and 38,000 children have received these devices (bit.ly/NIDCD-CIhttp://bit.ly/nidcd-ci). The numbers could grow much larger if the FDA expands its candidacy criteria.
“There are underserved populations who could benefit from cochlear implantation,” Dr. Dillon said. “Research has shown that subjects with more residual hearing and better speech-perception abilities than [allowed by the] current criteria would benefit from cochlear implantation.”
A cochlear implant consists of an implantable device that electrically stimulates surviving nerve fibers within the inner ear to produce perceptions of sound in patients with significant sensorineural hearing loss. The implanted device is controlled by an external sound processor that converts acoustic sound signals into patterns of electrical stimulation.
In the United States, the FDA has approved cochlear implant systems from three manufacturers: Advanced Bionics, Cochlear, and MED-EL. Each manufacturer has its own FDA-sanctioned indications for adults and children.
In general, adults must have bilateral sensorineural hearing loss and obtain limited benefit from appropriately fitted binaural hearing aids in order to be considered for a cochlear implant under these indications. Children 12 to 24 months of age typically must have bilateral profound sensorineural deafness and show limited benefit from appropriate binaural hearing aids, whereas children two years of age or older may demonstrate severe to profound hearing loss bilaterally.
Contraindications to cochlear implantation include deafness due to lesions of the eighth cranial nerve or brainstem, active middle ear disease, and certain hematologic, pulmonary, and cardiac conditions that preclude cochlear implant surgery. The absence of cochlear development as demonstrated on CT scan remains an absolute contraindication.
To determine which patients are cochlear implant candidates, a battery of audiological and medical tests are used. Audiological tests evaluate the degree of hearing loss as well as the patient's ability to detect sounds and recognize words or sentences when not using lipreading.
Preoperative speech and language testing is especially important for children.
Medical tests help identify the cause of hearing loss and whether an alternative treatment is recommended. CT and MRI scans are used to evaluate the physical status of the cochlea and whether any abnormal anatomical variations might affect placement of the electrode array.
CURRENT CLINICAL TRIALS
Advances in electrode array design, surgical techniques, and signal-coding strategies are driving the expansion of cochlear implant candidacy, Dr. Dillon said.
“There is also a greater understanding of the benefits of combining electric and acoustic stimulation, which has been shown to improve speech perception in challenging background noise, localization, music perception, and subjective benefit as compared with either technology alone.”
However, more studies on the management of cochlear implant recipients are needed, including evaluations of fitting practices, listening configurations, aural rehabilitation, and follow-up care, Dr. Dillon said.
“Future research on nontraditional cochlear implant candidates should also assess outcomes beyond speech perception alone, such as music perception and quality of life.”
A number of clinical trials are now investigating the use of cochlear implants outside the FDA-approved indications, such as in patients with asymmetrical hearing loss or single-sided deafness.
Available management options for single-sided deafness include bone-anchored hearing implants and contralateral routing of signal (CROS) hearing aids. Both types of devices pick up sound from the poorer ear and transmit it to the normal hearing ear. They provide advantages but fail to address deficits that require binaural auditory processing. On the other hand, recent studies have suggested that cochlear implantation can benefit those with single-sided deafness by improving speech understanding and sound localization, and by suppressing tinnitus.
Other investigations are including participants who have greater speech recognition than the current cochlear implant indications allow. For example, one study is evaluating the safety and efficacy of expanding the criteria for cochlear implant candidacy used by the Centers for Medicare & Medicaid Services (CMS), which require test scores of 40 percent correct or lower in the best-aided listening condition on tape-recorded tests of open-set sentence recognition.
“Unfortunately, CMS criteria are stricter than FDA indications,” said Teresa A. Zwolan, PhD, director of the Cochlear Implant Program at the University of Michigan, who is involved in the study. “The purpose is to evaluate outcomes in CMS beneficiaries who score between 40 and 60 percent pre-implant on sentences with hearing aids,” she said.
This Coverage with Evidence Development study, which was approved by CMS and is coordinated by the American Cochlear Implant Alliance, will examine audiologic and quality-of-life outcomes in adults with bilateral sensorineural hearing loss who are age 65 and older and eligible for CMS as a primary source of medical insurance coverage. Upon completion of the study, CMS will determine if it will expand its criteria.
For Dr. Zwolan, the biggest challenge in expanding cochlear implant candidacy is enrolling participants in studies, possibly because of professionals’ lack of awareness of the trials or concerns regarding insurance coverage when cochlear implantation is evaluated as part of a clinical trial. Special considerations also come into play for nontraditional candidates who present with more residual hearing than traditional criteria permit.
“While new internal devices and enhanced surgical techniques have improved the likelihood that hearing will be preserved post-implant, it's important that the patient understands both the potential risks and benefits involved in cochlear implant surgery,” Dr. Zwolan said. “Although rare, the potential exists that their hearing could be worse off with a cochlear implant.”
Outcomes for traditional and nontraditional candidates can vary widely, with many determinants affecting whether cochlear implantation is successful.
“With adults, the greatest factor influencing success appears to be the length of time between the onset of deafness and the receipt of a cochlear implant,” Dr. Zwolan said. “Patients with the shortest duration of deafness tend to do the best, so it is important for us to implant adults soon after they reach candidacy.”
Meanwhile, the best prognosis for successful development of spoken language skills is expected for children who receive a cochlear implant at a young age, participate in spoken language therapy, and have a normal cognitive status, an anatomically normal cochlea, and involved and supportive families and schools, Dr. Zwolan said.
“Children who meet these criteria and receive an implant prior to the age of 18 months will likely obtain speech, language, academic, and reading skills comparable to their peers with normal hearing by the time they are in kindergarten.”
SPECIAL PEDIATRIC CONSIDERATIONS
The importance of early intervention cannot be overstated, noted John K. Niparko, MD, professor and chair of the Department of Otolaryngology–Head & Neck Surgery at the Keck School of Medicine of the University of Southern California (USC). Dr. Niparko works with Laurie S. Eisenberg, PhD, professor of research otolaryngology at the Keck School of Medicine, and Margaret Winter, MS, associate professor of clinical otolaryngology at the Keck School of Medicine and an audiologist at the USC Caruso Family Center for Childhood Communication.
“Young children's struggle to understand the sounds of speech while they mature through critical phases of early development can seriously constrain the eventual acquisition of spoken language in all of its forms,” Dr. Niparko said. “The resultant delays can produce gaps that may be impossible to overcome. If amplification is not enabling children to achieve their early milestones, candidacy should be considered as early as possible.”
But just because children can receive a cochlear implant doesn't necessarily mean they should, Dr. Eisenberg added.
“The goal of cochlear implantation is less about providing hearing per se than about enhancing communication skills,” she said. “A team might choose not to recommend an implant if the team feels the child is better served by focusing on development of a visual communication strategy, even if the child has an implantable cochlea.”
There are still many questions about expanding cochlear implant candidacy to nontraditional candidates. For example, it isn't yet clear where the dividing line is when considering risk versus benefit in the implantation of a young infant, or whether the implantation of children with severe cognitive delays yields sufficient benefit—perhaps other than the development of spoken language—to warrant surgery.
“For children with severe cognitive or global processing deficits, inputs from a cochlear implant may never give rise to meaningful perceptions,” Dr. Niparko said. “But this requires care in thought and assessment of a child's developmental potential in the context of their hearing loss and other handicapping conditions.”
To identify and manage nontraditional cochlear implant candidates, a team-based approach is crucial. Effective communication with the patient's family is most essential when it comes to diagnostics, hearing aid fitting, and implant device maintenance and programming, Ms. Winter said.
“The entire family should become well versed in the use and maintenance of a child's worn technology. All audiologists, speech–language pathologists, and educational and day care personnel are team members who play a role in a child's success. Without such comprehensive support, valuable time is lost in providing the kind of rich experience with spoken language that is critical to outcomes for a child with hearing loss.”
In the end, the appropriate identification and management of nontraditional candidates can go a long way toward achieving success.
“With cautious relaxation of criteria has come the observation that the majority of children with severe and profound sensorineural hearing loss can enjoy a full array of life options related to their schooling, and ultimately their vocational and social–emotional health, through the use of cochlear implants, possibly in combination with hearing aids,” Dr. Niparko said.
“Early, effective sensory perceptions are critical to every aspect of development, and advances in digital and implantable technology have opened remarkable opportunities for kids with severe and profound sensorineural hearing loss.”