In one of the largest retrospective studies of its kind, researchers analyzed data from approximately 96,000 ears and created a word score model that can determine the amount of hidden hearing loss or cochlear nerve damage in people. people.
A word score model that can assess the degree of hidden hearing loss in human ears has been created by researchers at Massachusetts Eye and Ear.
Researchers at Eaton-Peabody Laboratories at Massachusetts Eye and Ear calculated average age-specific speech scores from recordings of approximately 96,000 ears assessed at Massachusetts Eye and Ear in a new study just released. published in Scientific reports. After that, they compared the results to previous research at Massachusetts Eye and Ear that had monitored typical cochlear nerve fiber loss over time. The researchers created an estimate of the relationship between speech scores and nerve survival in humans by combining the two data sets.
New model improves patient assessments of cochlear nerve damage and speech intelligibility deficits caused by neural loss, says Stéphane F. Maison, Ph.D., CCC-A, lead study author and associate professor of otolaryngology. Head and Neck Surgery at Harvard Medical School. Maison is also the Principal Investigator of Eaton-Peabody Laboratories. The model also provides methods for calculating the effectiveness of interventions for hearing loss, such as the use of hearing aids and personal sound amplification devices.
“Before this study, we could either estimate neural loss in a living patient using a long battery of tests, or measure cochlear nerve damage by removing his temporal bones when he died,” said the Dr. House. “Using ordinary speech scores from hearing tests – the same ones collected in clinics around the world – we can now estimate the number of missing neural fibers in a person’s ear.”
Uncover hidden hearing loss
The two main factors that determine a person’s ability to hear are audibility and intelligibility. Sensory cells called hair cells in the inner ear play a role in audibility of sound, that is, how loud a sound is to be heard. Hair cells deliver 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 the clarity or understanding with which the central nervous system processes sound.
For many years, researchers and healthcare professionals believed that the primary cause of hearing loss was hair cell degeneration and that cochlear nerve damage only became severe after hair cell loss. Hair cell health can be determined by an audiogram, which has long been considered the gold standard of hearing testing. Patients with a normal audiogram were given a clean bill of health while claiming to have difficulty hearing in noisy environments, as the nerve loss was thought to be secondary to hair cell loss or dysfunction. Experts now realize that the audiogram is not informative about the state of the auditory nerve.
“This explains why some patients who report difficulty understanding a conversation in a busy bar or restaurant may undergo a ‘normal’ hearing test. Likewise, this explains why many hearing aid users who receive amplified sounds still struggle with speech intelligibility,” Dr. Maison said.
In 2009, Mr. Charles Liberman, Ph.D., and Sharon Kujawa, Ph.D., Principal Investigators at Eaton-Peabody Laboratories, upended the way scientists thought about hearing when they discovered hearing loss hidden. Their results revealed that cochlear nerve damage preceded hair cell loss due to aging or noise exposure and suggested that by not providing information about the cochlear nerve, audiograms had no effect. actually assessed the full extent of damage to the ear.
Building a model to predict cochlear nerve damage
In the study, Dr. Maison and his team used a speech intelligibility curve to predict what an individual’s speech score should be based on their audiogram. They then measured the differences between the predicted word recognition scores and those obtained during the patient’s hearing assessment.
Since the word list was presented at a level well above the patient’s hearing threshold – where audibility is not an issue – any difference between the predicted score and the measured score would have reflected hearing deficits. intelligibility, explained Dr. Maison.
After looking at a number of factors, including cognitive deficits that can accompany aging, the researchers argued that the size of these discrepancies reflected the amount of cochlear nerve damage, or hidden hearing loss, that a person had. They then applied measures of neural loss from existing histopathological data of human temporal bones to come up with a predictive model based on a standard hearing test.
The results confirmed an association between lower speech scores and greater amounts of cochlear nerve damage. For example, the worst scores were found in patients with Ménière’s disease, which is consistent with temporal bone studies showing dramatic loss of cochlear nerve fibers. Meanwhile, patients with conductive hearing loss, drug-induced hearing loss, and normal age-related hearing loss – etiologies with the least cochlear nerve damage – showed only moderate to small deviations.
Changing the research landscape for hidden hearing loss 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 eligible for traditional hearing aids, especially if they have mild to moderate high frequency hearing loss. Knowing the extent of neural damage should inform clinicians on the best ways to meet a patient’s communication needs and suggest appropriate interventions in addition to the use of effective communication strategies.
This new research was part of a five-year, $12.5 million P50 grant from the National Institutes of Health to better understand the prevalence of hidden hearing loss.
By identifying patients most likely to have greater cochlear nerve damage, Dr. Maison believes this model could help clinicians assess the effectiveness of traditional and newer sound amplification products. The researchers also hope to introduce new audiometric protocols to further refine their model and provide better interventions by assessing word performance scores in noise, as opposed to silence.
Reference: “Predicting Neural Deficits in Sensorineural Hearing Loss from Word Recognition Scores” by Kelsie J. Grant, Aravindakshan Parthasarathy, Viacheslav Vasilkov, Benjamin Caswell-Midwinter, Maria E. Freitas, Victor de Gruttola, Daniel B. Polley, Mr. Charles Liberman, and Stéphane F. Maison, June 23, 2022, Scientific reports.
In addition to Dr. Maison, study co-authors include Kelsie J. Grant, Aravindakshan Parthasarathy, Viacheslav Vasilkov, Benjamin Caswell-Midwinter, Maria E. Freitas, Daniel B. Polley, Mr. Charles Liberman of Massachusetts Eye and Ear / Harvard Medical School and Victor DeGruttola of Harvard TH Chan School of Public Health.
This study was funded by the National Institutes of Health.