Cochlear Implantation Improves Hearing in Elderly

As the baby boomer generation ages, they may all have one topic of conversation they can share--sensorineural hearing loss. According to the National Institutes of Health, 15 percent of people between 55 and 64 years of age, 30 percent of people between 65 and 74 years of age, and 40 percent of people over 75 years of age have a hearing loss that affects communication.

This condition is caused by aging and noise exposure that first damages and then eventually destroys outer hair cells in the organ of Corti. As the hearing loss becomes more severe, inner hair cells are eventually affected. Most causes of sensorineural hearing loss first alter the basal end of the basilar membrane, so that hearing for high-frequency sounds is decreased. As the hearing loss worsens, more apical ends of the basilar membrane are destroyed, resulting in the worsening of hearing in the mid- and low-frequency regions.

The rehabilitation of patients with sensorineural hearing loss has been revolutionized by the introduction of the cochlear implant, which is an electronic device that directly stimulates the cochlear nerve and improves sound awareness and speech perception. The benefits of implantation have been well documented with improved audiological measures, recognition of environmental sounds and psychosocial benefits such as enhancement of self-esteem.

A team of researchers have completed a new study that assessed outcomes for cochlear implantation in an elderly population. They found that the aging test subjects showed significant improvement in auditory performance tests following cochlear implantation compared with their preimplantation scores, but performed less well than younger patients.

The results defy expectations that the elderly may have poorer rehabilitative outcomes following implantation. First, previous animal and human studies have shown that there is age-related degeneration of the spiral ganglion cells. As auditory neurons are critical for the success of cochlear implantation, availability of limited population for stimulation may negatively impact outcome. In addition to degeneration in the peripheral auditory system, there is also evidence for deficits in the central auditory pathways and integration pathways as people age. Consequently, there is concern that this "central presbyacusis" may also negatively impact on the benefit of implantation in the elderly.

With those concerns in mind, an investigation was undertaken to examine the surgical and auditory rehabilitative outcome after cochlear implantation in patients aged 70 years and older and compare it with a cohort of younger individuals. The authors of "Cochlear Implant Outcomes in the Elderly," Veronique Chatelin MD, Eugene J. Kim MD, Anil K. Lalwani MD, Jannine Larky, and Colleen Polite, from the Douglas Grant Cochlear Implant Center, Department of Otolaryngology--Head and Neck Surgery, University of California-San Francisco, CA; and Colin Driscoll MD, and Laura Price, at the Department of Otorhinolaryngology, Mayo Clinic, Rochester, MN will present their findings at the annual meeting of the American Neurotology Society http://itsa.ucsf.edu/~ajo/ANS/ANS.html held May 3, 2003, at Gaylord Opryland Hotel, Nashville, TN.

Methodology: A retrospective chart review was performed using the records of the cochlear implant groups at the University of California, San Francisco and the Mayo Clinic. Sixty-five subjects aged more than or equal to 70 years at the time of implantation were identified and compared to a group of younger patients younger than 70 at the time of implantation. All subjects were implanted from 1991 to 2002 with either the Clarion or the Nucleus device. Data was collected using a repeated-measures, single-subject experiment in which each subject served as his or her own control. Audiological and speech perception scores were obtained preoperatively with hearing aids and compared to postoperative scores to determine improvement in speech perception ability. Patients were seen at regular intervals for data collection, testing, and programming of their cochlear implants. All subjects underwent standardized open-set speech recognition testing preimplantation (aided) at three, six and 12 months. Patients were assessed with recorded versions of monosyllabic Consonant Nucleus Consonant (CNC) words, Central Institute for the Deaf (CID) sentences, and Hearing in Noise Test (HINT) sentences. The patient's preferred speech-processing strategy was used. Surgical complications were compiled for each subject.

Results: Of 65 elderly patients who received implantation, 33 were men and 32 were women with a mean age of 76 years. Time length of deafness before implantation varied from one to 62 years, with a mean and median length of six and nine years, respectively. A total of 101 randomly selected younger patients (34 males and 67 females with a mean age of 48 years at implantation) undergoing implantation during the same time interval were included in the control group.Key outcomes measured and results include:

Surgical Complications: There were no complications of general anesthesia for both young and elderly patients. All elderly patients underwent successful placement of the internal component and device activation. There were two elderly patients who experienced facial nerve stimulation from the implant requiring exclusion of the single culprit electrode in each of the patients.

Auditory Rehabilitation: Both young and elderly patients showed significant improvement compared with preimplantation scores obtained in the best aided condition. Near-maximal improvement in speech understanding was observed in the majority of patients by three months post-implantation. Specific audiometric data for the young group showed improvement at 12 months on CID sentences from a preoperative mean and median of 17 and 3 percent, respectively, to a mean and median of 78 and 92 percent, respectively. In comparison, the elderly group showed improvement at 12 months on CID sentences from a preoperative mean and median of 17 and five percent, respectively, to a mean and median of 62 and 48 percent, respectively.

Subjects also showed similar improvements in the other audiometric measures using CNC words and HINT sentences. Performance in the young group with CNC words increased from a preoperative mean and median of four and zero percent, respectively to a mean and median of 45 and 43 percent, respectively, at 12 months. For the same time interval, elderly scores with CNC words increased from a preoperative mean and median of nine and five percent, respectively, to a mean and median of 36 and 35 percent, respectively. With HINT sentences, the young group improved from a preoperative mean and median of 11 and zero percent, respectively, to 79 and 85 percent, respectively, at 12 months. For the same time interval, the elderly group improved from a preoperative mean and median of 18 and 12 percent, respectively, to 62 and 73 percent, respectively.

When compared to the younger control group, the elderly population showed slightly worse outcomes in all three measures. Generalized estimating equations were used to compare rates of change between both groups. Two-tailed chi-squared analysis showed a statistically significant difference with CNC scores and close to statistically significant differences with CID and HINT scores.

Conclusions: Cochlear implantation in the elderly is well tolerated and provides marked improvement in auditory performance. However, this study revealed that elderly subjects have slightly less performance enhancement compared with younger patients, which is possibly due to age-related changes in the auditory system. Nonetheless, the findings suggest that cochlear implantation is a viable treatment for severe-profound hearing loss in the elderly population and should not be overlooked in this demographic group.