A model developed at Harvard can identify your hidden hearing loss

The researchers’ word-of-mouth model can estimate hidden hearing loss.

In one of the largest retrospective studies of its kind, researchers analyzed data from approximately 96,000 ears and created a word-scoring model that can determine the extent of hidden hearing loss or cochlear nerve damage in people.

Researchers from Massachusetts Eye and Ear.

Researchers at Eaton-Peabody Laboratories at the Massachusetts Eye and Ear Center calculated average age-specific speech scores based on recordings of approximately 96,000 ears evaluated by Massachusetts Eye and Ear in a new study that was just published in Scientific reports. They then compared the results to previous studies at the Massachusetts Eye and Ear Center that monitored the typical loss of cochlear nerve fibers over time. The researchers created an estimate of the relationship between speech performance and neural survival in humans by combining two sets of data.

The new model improves the assessment of cochlear nerve damage in patients and speech intelligibility deficits caused by neuronal loss, says Stefan F. Mezon, Ph.D., CCC-A, the study’s lead author and assistant professor of otolaryngology. Head and neck surgery in Harvard Medical School. Mason is also a principal investigator at Eaton-Peabody Laboratories. The model also provides methods for calculating how well hearing loss interventions, such as the use of hearing aids and personal sound amplification devices, are working.

“Prior to this study, we could either assess nerve loss in a living patient using a lengthy test battery, or measure cochlear nerve damage by removing their temporal bones when they had died,” Dr. Mason said. “Using routine speech scores from hearing tests—the same ones collected in clinics around the world—we can now estimate the number of nerve fibers missing in a person’s ear.”

Detecting hidden hearing loss

The two main factors that determine a person’s ability to hear are audibility and intelligibility. Sensory cells, known as hair cells in the inner ear, play a role in sound audibility, or how loud a sound must be to be heard. Hair cells send electrical impulses to the cochlear nerve in response to sound, and the cochlear nerve then sends these signals to the brain. The ability of the cochlear nerve to transmit these signals effectively affects how clearly and intelligibly the central nervous system processes sound.

For many years, researchers and medical professionals believed that the primary cause of hearing loss was hair cell degeneration and that damage to the cochlear nerve only became serious after the loss of hair cells. Hair cell health can be determined by an audiogram, which has long been considered the gold standard for hearing testing. Patients with normal audiograms were considered clear but claimed to have hearing problems in noisy environments because nerve loss was thought to be secondary to hair cell loss or dysfunction. Specialists now understand that the audiogram is not informative about the condition of the auditory nerve.

“This explains why some patients who report difficulty understanding conversation in a busy bar or restaurant may pass a ‘normal’ hearing exam. It also explains why many hearing aid users who receive amplified sounds still have difficulty with speech intelligibility,” said Dr. Mason.

In 2009, M. Charles Lieberman, Ph.D., and Sharon Kujawa, Ph.D., principal investigators at the Eaton-Peabody Laboratory, revolutionized the way scientists think about hearing when they discovered hidden hearing loss. Their findings showed that damage to the cochlear nerve precedes hair cell loss from aging or noise exposure, and suggested that by not providing information about the cochlear nerve, audiograms did not actually assess the full extent of ear damage.

Building a model to predict cochlear nerve damage

In the study, Dr. Mason and his team used a speech intelligibility curve to predict what a person’s speech score should be based on their audiogram. They then measured the differences between the predicted word recognition scores and the scores obtained during the patient’s hearing evaluation.

Because the word list was presented at a level well above the patient’s hearing threshold—if audibility is not a problem—any difference between the predicted and measured scores would reflect a deficit in intelligibility, Dr. Mason explained.

After considering a number of factors, including the cognitive deficits that can accompany aging, the researchers argued that the size of these discrepancies reflects the degree of cochlear nerve damage or hidden hearing loss in a person. They then applied measures of nerve loss based on existing histopathological data from human temporal bones to create a predictive model based on standard hearing screening.

The results confirmed an association between worse speech scores and more cochlear nerve damage. For example, the worst scores were found in patients with Ménière’s disease, consistent with studies of the temporal bone that showed a dramatic loss of cochlear nerve fibers. Meanwhile, patients with conductive hearing loss, drug-induced hearing loss, and normal age-related hearing loss—the etiologies with the least amount of cochlear nerve damage—showed only moderate to small discrepancies.

The changing landscape of hidden hearing loss research and beyond

According to the World Health Organization, more than 1.5 billion people live with some degree of hearing loss. Some of these people may not be good candidates for traditional hearing aids, especially if they have mild to moderate high-frequency hearing loss. Knowing the extent of neural damage should inform clinicians about the best ways to meet the patient’s communication needs and suggest appropriate interventions beyond the use of effective communication strategies.

This new research was part of a five-year, $12.5 million grant from the National Institutes of Health to better understand the prevalence of hidden hearing loss.

By identifying which patients are most likely to have cochlear nerve damage, Dr. Mason believes this model can help clinicians evaluate the effectiveness of traditional and new sound amplification products. The researchers also hope to introduce new audiometric protocols to further refine their model and suggest better interventions by assessing measures of word performance in noise as opposed to quiet.

Reference: “Prediction of Neural Deficit in Sensorineural Hearing Loss Based on Word Recognition Scores” by Kelsey J. Grant, Aravindakshan Parthasarathy, Vyacheslav Vasilkov, Benjamin Caswell-Midwinter, Maria E. Freitas, Victor de Gruttola, Daniel B. Poli, M. Charles Lieberman, and Stephan F. Mason, 23 June 2022. Scientific reports.
DOI: 10.1038/s41598-022-13023-5

In addition to Dr. Mason, co-authors of the study include Kelsey J. Grant, Aravindakshan Parthasarathy, Vyacheslav Vasilkov, Benjamin Caswell-Midwinter, Maria E. Freitas, Daniel B. Polley, M. Charles Lieberman of Massachusetts Eye and Ear/Harvard Medical School, and Victor DeGrutala of the Harvard T. Chan School of Public Health.

This study was funded by the National Institutes of Health. A model developed at Harvard can identify your hidden hearing loss

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