Advances in Otolaryngology - Head and Neck Surgery

It has long been assumed that people can live just fine with unilateral hearing. But studies have shown that single-sided deafness (SSD) has adverse effects that go beyond not being able to hear, including cognitive deficits. While hearing aids may help some individuals with SSD, others require a more intensive intervention. A unilateral cochlear implant may be the solution.

Following the FDA approval of cochlear implant models for use in people with SSD, Hae-Ok Ana Kim, MD, a neurotologist at NewYork-Presbyterian/Columbia, is leading a study to understand how the implants affect brain activity.

"The traditional dogma has been that if you have one hearing ear, you can get by in life. But there has been much research in the last decade showing that the brain is like a muscle: If you don't use it, you lose it," said Dr. Kim. "If someone with hearing loss—even in one ear—does not wear a hearing aid or take other steps to address deafness, there is an increased risk of cognitive decline, dementia, and depression. Imaging studies show reorganization of the cortical architecture, with shrinkage of auditory centers and enlargement of the visual cortex."

SSD may be caused by pathology, such as an acoustic neuroma, or be idiopathic. Some people develop it in conjunction with inner ear autoimmune disease, where the body sees the inner ear as foreign and mounts an inflammatory attack. SSD can be quite profound and not amenable to correction with a hearing aid. "That's why cochlear implants are an important option for these patients," noted Dr. Kim.

Dr. Ana Kim

In a prior study, she and her fellow investigators reported that patients with SSD related to sudden sensorineural hearing loss or Meniere's disease demonstrated excellent speech perception and quality of life outcomes after unilateral cochlear implantation. The benefits of cochlear implantation versus a hearing aid for SSD include:

• Better sound localization (being able to pinpoint where a sound is coming from)
• Binaural loudness summation: speech and sound are louder when hearing is accomplished with both ears
• Squelching, where the brain filters out noise and only processes what is meaningful

Dr. Kim is now leading an ongoing pilot study of people having single-sided cochlear implant surgery. Participants have a PET/CT scan before the surgery and then again six months later. It can take about three months for the brain to adapt to the cochlear implant and by six months, patients have typically reached the plateau phase. The study, which has four subjects enrolled so far, may extend beyond six months to assess the long-term benefits and effects of unilateral cochlear implantation for SSD.

“If someone with hearing loss—even in one ear—does not wear a hearing aid or take other steps to address deafness, there is an increased risk of cognitive decline, dementia, and depression.” — Dr. Ana Kim

Because each participant has adequate hearing in one ear and a cochlear implant for SSD in the other, the investigators can compare the right and left sides of the brain on imaging scans. They will compare the imaging findings with clinical data such as:

• Speech understanding, as measured by standard audiometry
• Sound localization
• Quality of life, as assessed by questionnaire

Two of the study participants had implant surgery in January 2023, and their follow-up PET/CT and other test results should be available this summer. The other two patients are having cochlear implantation this summer and are expected to undergo final testing in December 2023.

“Whether someone is a teenager or a 70-year-old, assessing hearing is just as important as determining whether a patient has high blood pressure or diabetes.” — Dr. Ana Kim

Despite the benefits of unilateral cochlear implantation for SSD, patients may have trouble getting their insurance provider to cover the treatment. It is not unusual for an insurance provider to ask the doctor to prescribe a hearing aid instead, which, in the case of SSD, is likely to be ineffective. Dr. Kim emphasizes that it is not just important to hear sounds, but to understand words. In Europe, cochlear implants have been used to treat SSD for the last five years.

She encourages physicians to screen their patients for hearing loss at annual physical exams, regardless of their age. "Whether someone is a teenager or a 70-year-old, assessing hearing is just as important as determining whether a patient has high blood pressure or diabetes," Dr. Kim concluded. "It should be part of routine health wellness and maintenance."