Chronic Middle-Ear Infections and Unilateral Conductive Hearing Loss Can Impair Speech Recognition

Summary: Untreated ear infections and other conditions that cause long-term hearing loss in one ear can lead to nerve damage. This damage may cause lasting difficulties with speech recognition and processing, particularly in noisy environments.

Source: Massachusetts Eye and Ear Infirmary

Key finding: Chronic conductive hearing loss — often the result of middle-ear infections — has been associated with reduced speech-recognition ability, according to a study led by researchers at Massachusetts Eye and Ear and published in the journal Ear and Hearing. The study suggests that prolonged sound deprivation on one side may produce neural changes consistent with cochlear synaptopathy, sometimes called “hidden hearing loss.”

Conductive hearing loss occurs when sound transmission from the ear canal through the middle ear to the inner ear is impaired. This can reduce sound levels and make soft sounds difficult or impossible to hear. In contrast, sensorineural hearing loss results from damage to the inner ear or the auditory nerve, which prevents sound-induced vibrations from being converted properly into electrical signals sent to the brain.

Middle-ear infections (otitis media) are extremely common in young children. In the United States, roughly three out of four children experience at least one episode before age three. These infections can recur and sometimes persist for months, creating intermittent or chronic unilateral conductive hearing loss that may hamper speech and language development and school performance.

In the retrospective study, researchers reviewed audiology records for 240 patients seen at the Massachusetts Eye and Ear Audiology Department who presented with either acute or chronic conductive hearing loss but showed normal sensorineural test results. The team compared speech-recognition performance between the affected ear and the better ear. Patients with long-standing, moderate-to-moderately-severe conductive hearing impairment demonstrated significantly lower speech-recognition scores on the impaired side even when speech was presented at levels high enough to be audible.

These human clinical findings align with previous animal research by the study’s lead investigator, Stéphane F. Maison, PhD. In 2015, studies in adult mice showed that prolonged conductive impairment can lead to loss of synaptic connections between the inner ear’s sensory hair cells and the auditory nerve fibers that transmit signals to the brain. That type of synaptic damage was first identified after noise exposure and is commonly referred to as cochlear synaptopathy or “hidden hearing loss” because it may not appear on standard hearing-threshold tests but can degrade suprathreshold tasks such as speech recognition in noise.

“Our results suggest that chronic sound deprivation can lead to speech-recognition difficulties consistent with cochlear synaptopathy,” said Stéphane F. Maison, PhD, a principal investigator in the Eaton-Peabody Laboratories at Massachusetts Eye and Ear and an Assistant Professor of Otolaryngology—Head and Neck Surgery at Harvard Medical School. “Clinicians should consider amplification and other rehabilitation strategies when managing unilateral conductive hearing loss to reduce the risk of long-term neural deficits.”

Children with asymmetric or unilateral hearing loss are already known to face higher rates of academic, social, and behavioral challenges. The study’s authors emphasize that early identification and appropriate management of conductive hearing loss are important for preventing or minimizing longer-term communication difficulties. Even when one ear remains functional, leaving the poorer ear untreated may allow neural changes to develop that impair speech perception over time.

Funding: The research was supported by the National Institute on Deafness and Other Communication Disorders of the National Institutes of Health (grant P50 DC015857).

Study authors and affiliations: Co-authors include Masahiro Okada, MD (Department of Otolaryngology, Ehime University Graduate School of Medicine, Japan); D. Bradley Welling, MD (Chief of Otolaryngology, Massachusetts Eye and Ear and Massachusetts General Hospital; Walter Augustus LeCompte Professor and Chair of Otolaryngology, Harvard Medical School); and M. Charles Liberman, PhD (Director, Eaton-Peabody Laboratories, Massachusetts Eye and Ear; Harold F. Schuknecht Professor of Otolaryngology, Harvard Medical School).

Source:
Massachusetts Eye and Ear Infirmary
Media contacts:
Ryan Jaslow — Massachusetts Eye and Ear Infirmary
Image source:
The image is in the public domain.

Related research and context

Earlier investigations led by the same group explored how noise exposure can damage vestibular and auditory pathways. For example, research on the effect of noise exposure on cervical vestibular evoked myogenic potentials (cVEMPs) found that a substantial portion of participants with asymmetric, noise-induced sensorineural hearing loss exhibited abnormal cVEMP responses. Those findings support the broader concept that both cochlear and related vestibular pathways can be vulnerable to noise-related or deprivation-related damage. Abnormal cVEMP responses were more common in the ears with poorer hearing and were associated with greater high-frequency threshold loss.

Clinical implications: Health professionals who evaluate unilateral conductive hearing loss should weigh the potential long-term neural consequences of untreated sound deprivation. Consideration of amplification devices, monitoring, and early intervention could help preserve speech-recognition performance and reduce the risk that temporary or chronic middle-ear conditions will lead to persistent neural deficits.