Hearing restoration crucial in dementia prevention

Hearing loss is a major risk factor for dementia, shows latest research on aging. “It is well established now that the one thing that we can do as ENT surgeons to reverse or slow down dementia in older persons is to improve their hearing,” said Dr Euan Murugasu, senior consultant ENT surgeon, Mount Elizabeth Novena Hospital, Singapore, at the recent ENT Summit Asia 2025 in Kuala Lumpur.

The 2024 update of the Lancet Commission on dementia states that hearing loss elimination can lead to 7 percent reduction in dementia cases. [Lancet 2024;404:572-628] Hearing loss was reported to almost double the risk of dementia, which is similar to the risk due to a traumatic brain injury. [Lancet 2020;396:413-446] When people aged 45 to 65 experience hearing loss, they are at high risk for dementia. [JAMA 2023;329:171-173]

Since hearing capacity exists on a spectrum, subclinical hearing loss can also increase the risk of dementia. [Lancet 2020;396:413-446] A longitudinal aging study in Singapore and Asia in 2018 also supports that hearing loss is a risk factor for dementia, in concordance with emerging evidence around the world, said Murugasu.

New technology in hearing restoration
Hearing aids may be the answer to restoring hearing and preventing dementia; they are cost-effective and minimally invasive. Studies have shown that the use of hearing aids, especially in high-risk population, led to significantly reduced risk of dementia. [Lancet 2024;404:572-628] “Hearing aid technology, depending on the preference and subsidies, is reaching a wider impact globally, but more needs to be done,” said Murugasu.

The choice of hearing aids is dependent on the extent of hearing loss, which should be assessed through a hearing test, said Associate Professor Dr Raymond Ngo, head and senior consultant, Department of Otolaryngology, Ng Teng Fong General Hospital, Singapore (Table 1). Hearing aids in wearables that can monitor noise exposure and track hearing health are also available for mild to moderate hearing loss, Ngo added.

Bone anchored hearing aid (BAHA) and bone conduction implant (BCI) are recommended for hearing loss due to chronic ear infections and congenital deformities in patients with normal bone-conduction thresholds. Cochlear implants are the last resort for patients with worsening hearing despite using hearing aids and are ideally utilized before patients become completely deaf to reduce the down time. Cochlear implants are also ideal for children who are born with severe to profound hearing loss and do not have adequate response to hearing aids, said Ngo.

Gene therapy is an emerging and promising treatment for genetic hearing loss and is most effective when administered before irreversible changes happen. In the process of gene therapy, the exact genetic variation that is causing the hearing loss must be identified first. Then a viral vector i.e., adeno-associated viruses (AAV), is utilized to transfer the normal genes into the inner ear via the round window, cochleostomy or the cerebrospinal fluid and cochlear aqueduct. The normal genes cause the sensory cells to function and activate the auditory nerve, which sends impulses to the brain, said Murugasu.

He added that a clinical trial in China showed gene therapy resulted in hearing recovery and improved speech recognition in five out of six children aged 1 to 7 years with DFNB9, a type of inherited deafness due to mutations in the OTOF gene. The three older children, with their cochlear implants turned off, could understand and respond to speech by 26 weeks, with two children able to recognize speech in a noisy room and have a telephone conversation. The younger participants showed improvement in the ability to recognize speech but were too young for some tests. The child who showed no improvement may have had an immune reaction to the viral vector. The trial is a collaboration between Harvard Medical School and the Fudan University’s Eye and ENT Hospital. [https://hms.harvard.edu/news/experimental-gene-therapy-enables-hearing-five-children-born-deaf]

Update on minimally invasive otologic surgery
Surgery is required in treating specific types of hearing loss, especially conductive hearing loss, by resolving problems in the outer and middle ear. Minimally invasive otologic surgery involving microscope, endoscope and exoscope is at the forefront of hearing restoration. Endoscopic ear surgery (EES) provides superior view of middle ear structures, particularly the difficult-to-view areas such as the anterior epitymphanum, the supratubal recess, the pro-tymphanum, and the retro-tymphanum. It has broadened the understanding on ventilation pathways in the middle ear and the attic and reduces morbidity.

While EES continues to improve, there are some limitations related to learning curve issues, ear canal stenosis, and gross mastoid involvement or disease. Thus, a group of highly specialized otologists promote methodological research and teaching of EES under the auspices of the International Working Group on Endoscopic Ear Surgery (IWGEES). The group believes that otologists should master working with both the endoscope and microscope to allow for improved understanding and treatment of ear pathologies. He emphasized that the microscope is still an important and integral part of the surgical armamentarium.