Could Cochlear Implants Cause Harm to Hearing Over Time?

People who get cochlear implants to treat severe hearing loss may develop new bone growth in the ear — and it may lessen any hearing they have left, a new study hints.

The researchers found that among 100-plus adults with cochlear implants, two-thirds showed evidence of new bone formation near the implant within four years. And of patients who still had some hearing when they received the implant, those with new bone growth showed more hearing loss over time.

However, no one with a cochlear implant should be alarmed by the findings, stressed researcher Dr. Floris Heutink, of Radboud University Medical Center, in the Netherlands.

"Cochlear implantation allows most candidates to tremendously improve speech perception compared to their hearing situation (before), despite the possible presence of new bone formation," Heutink said.

Cochlear implants are small electronic devices that send sound signals from the environment directly to the ear's auditory nerve, bypassing damaged portions of the ear. They can provide some sense of sound to people who are deaf or severely hard-of-hearing — typically enough to help them understand speech.

The implant has an external portion that sits behind the ear and picks up sounds with a microphone. Those signals are sent to a receiver implanted under skin, and then transmitted to tiny electrodes implanted in the cochlea (a part of the inner ear).

It's already known that in people who have some hearing ability left, cochlear implants can sometimes diminish that "residual" hearing.

Studies have also shown that the implanted electrodes can spur inflammation that may lead to fibrosis (tissue growth), including new bone formation.

But, Heutink said, it has not been clear exactly when that bone growth happens, or if it's related to any residual hearing loss.

In this study, Heutink's team was able to spot new bone growth using high-resolution CT scans, and correlate it with diminishing hearing in the ear with the implant.

None of that, however, means people with cochlear implants should be getting CT scans, said Dr. Maura Cosetti, who directs the cochlear implant program at the New York Eye and Ear Infirmary of Mount Sinai, in New York City.

For one, there's no clear way to use that CT scan information. Various factors can contribute to residual hearing loss, Cosetti noted, and it's not yet known how new bone formation fits in — or what to do about it.

People with cochlear implants already regularly have their hearing and quality of life assessed — and that's what they should continue to do, said Cosetti, who was not involved in the study.

The findings were published online Dec. 7 in the journal Radiology. They're based on 123 patients, average age 63, who received cochlear implants at Radboud. The patients underwent CT scans about four years later, on average.

At that point, 68% showed signs of new bone growth near at least one implanted electrode, the study found.

There were 24 patients who still had some hearing ability when they received the implant. In that group, those with new bone formation showed more residual hearing loss in the implanted ear, the researchers reported. Overall, 48% had preserved their level of hearing, versus almost 79% of those with no signs of new bone growth in the ear.

The study received funding from Med-El, an Austrian cochlear implant maker that is developing a version with electrodes that contain the anti-inflammatory drug dexamethasone. The idea is to reduce inflammation and tissue damage that can happen post-implantation.

But for now, Heutink said, more research is needed to better understand how new bone growth might affect cochlear implant patients' hearing — and whether somehow preventing that tissue formation has benefits.

Cosetti said there is growing interest in whether and how residual hearing might be preserved in people with cochlear implants. Traditionally, she noted, the implants were reserved for people with profound deafness. But an increasing number of people with some residual hearing are receiving them, too.

More information

The U.S. National Institute on Deafness and Other Communication Disorders has more on cochlear implants.

SOURCES: Floris Heutink, MD, MSc, department of otorhinolaryngology, Radboud University Medical Center, Nijmegen, the Netherlands; Maura Cosetti, MD, director, cochlear implant program, Ear Institute at New York Eye and Ear Infirmary of Mount Sinai, and associate professor, otolaryngology and neurosurgery, Icahn School of Medicine at Mount Sinai, New York City; Radiology, Dec. 7, 2021, online