Severe hearing loss in teens, young adults often linked to enlarged vestibular aqueduct

Patients with severe hearing loss in their teens and 30s are more likely to have hereditary hearing loss known as enlarged vestibular aqueduct. According to a new study, cochlear implant surgery at this age tends to have a better prognosis compared to when it is performed in childhood.

Seoul National University Bundang Hospital (SNUBH) said Wednesday that a research team has confirmed it by conducting a retrospective study of 421 patients who underwent cochlear implant surgery at the hospital from 2018 to 2022, including 63 patients who underwent their first cochlear implant surgery between their teens and 30s.

The study was led by Professor Choi Byung-yun from the Department of Otolaryngology at SNUBH and Professor Choe Go-un from the Department of Otolaryngology at Chungnam National University Sejong Hospital.

Cochlear implant surgery is performed on patients with severe or profound hearing loss that is not helped by hearing aids, using electrodes implanted in the cochlea located in the inner ear to convert sound into electrical signals. A cochlear implant comprises electrodes inserted into the cochlea, an internal device implanted under the skin, and an external device called a speech processor, attached to the scalp with magnets. After surgery, external sounds are transmitted to the internal device through the speech processor, and the transmitted sounds are converted into electrical signals that travel through the cochlear nerve to reach the brain.

Cochlear implant surgery is the only safe and effective method to restore hearing for patients with severe hearing loss that cannot be adequately addressed with hearing aids. Since it is mostly performed on infants and the elderly, it has been well-studied. However, not much has been reported on the causes and outcomes of hearing loss in patients in their teens to 30s who have undergone cochlear implant surgery.

The researchers first investigated the causes of hearing loss by performing molecular genetic testing on DNA samples from oral mucosal cells or blood from 61 of the 63 patients. In 40 patients (65.2 percent), a genetic cause of hearing loss was identified, and more than a third of these were DFNB4, also known as enlarged vestibular aqueduct (EVA). There are several types of hearing loss caused by genetic mutations, including DFNB1, DFNB4, and DFNA, with DFNB4 being the most common, as it is known to cause hearing loss due to a loss of function in a gene that produces a hearing-regulating protein.

Although cochlear implants are commonly associated with pediatric patients with vestibular aqueduct dilatation, this study found that individuals between the ages of 10 and 30 also undergo this procedure. This suggests that vestibular aqueduct dysplasia should be suspected in patients with severe hearing loss who visit the hospital for cochlear implantation in this age group, the researchers noted.

The researchers also conducted hearing assessments in patients more than three months post-cochlear implant and found that all 63 patients had an average sentence comprehension score of 80 percent. Specifically, univariate simple linear regression and multiple linear regression analyses were performed to determine the correlation between patient age, age at onset of hearing loss, duration of hearing loss, and preoperative speech intelligibility when assessing hearing.

Regression analysis showed that a longer duration of hearing loss before surgery was associated with better outcomes, while a later age at onset of hearing loss was linked to more favorable surgical results. It also found that the age of hearing loss and preoperative speech intelligibility had significantly affected the outcome. The later the age of hearing loss and the clearer the patient's pronunciation before surgery, the better the surgical prognosis.

"The study provides significant insights into the causes of hearing loss and prognostic factors for cochlear implant surgery in patients in their teens to 30s, a group that has been somewhat overlooked in other studies. In particular, patients with hearing loss in this age group are often indecisive and hesitant to undergo surgery, and providing them with prognostic factors that predict surgical outcomes and outcomes can be very motivating,” Professor Choi said.