Estimating Hidden Deafness | Harvard Medical School

Researchers at Mass Eye and Ear have developed a word-score model that can estimate the amount of deafness hidden in the human ear.

In a new study published on June 23 Scientific Reports, A team of researchers at Harvard Medical School at Massachusetts Eye and Years Eaton Peabody Laboratories determined an average voice score as a function of age from approximately 96,000 ear records examined by Mass Eye and Year.

The data were then compared to a previous study at Mass Eye and Ear, which tracked the mean loss of cochlear nerve fibers as a function of age. By combining both datasets, researchers constructed estimates of the relationship between people’s speech scores and neural survival.

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According to the principal investigator Stephen HouseThis new model, an HMS associate professor of otolaryngology head and neck surgery and a senior researcher at Mass Eye and Ear’s Eaton-Peabody Laboratories, provides a better assessment of patients’ cochlear nerve injury and associated speech intelligibility disorders. be connected. Nerve loss. This model also provides a way to estimate the effectiveness of deafness interventions, such as the use of personal sound amplification products and hearing aids.

“Before this study, we were able to use a long test battery to estimate nerve loss in living patients or measure cochlear nerve damage by removing the temporal bone at the time of death,” the Maison said. I am saying. “It is now possible to estimate the number of nerve fibers missing in the human ear using the same normal voice scores from hearing tests collected in clinics around the world.”

Reveal hidden deafness

Two main factors determine how well a person hears: audibility and comprehension. Hair cells, the sensory cells in the inner ear, contribute to the audibility of sound, the size needed to be able to detect it. When hair cells receive sound, they pass electrical signals to the cochlear nerve, which in turn passes those signals to the brain. How well the cochlear nerve relays these signals contributes to the clarity or intelligibility of the sounds processed within the central nervous system.

For years, scientists and clinicians have believed that hair cell deterioration is a major cause of deafness, and that cochlear nerve damage is widespread only after hair cell destruction. Audiograms, long considered the gold standard for hearing tests, provide information on hair cell health. Because nerve loss was thought to be secondary to hair cell loss or dysfunction, patients with normal audiograms were given a clean health bill, despite reports of hearing impairment in noisy environments. Was done. Experts understand why audiograms do not assess auditory nerve health.

“This explains why some patients who report difficulty understanding conversations in busy bars and restaurants undergo a” normal “hearing test. Similarly, it explains why many hearing aid users who receive amplified sound still struggle with audio intelligibility, “says the Maison.

In 2009, M. Charles RivermanProfessor Harold F. Schknecht of HMS Otology and Laryngology, and Sharon KujawaHMS Professor of Otorhinolaryngology Head and Neck Surgery, a senior researcher at the Eaton Peabody Institute, overturned scientists’ thinking about hearing when they discovered hidden deafness. Their findings reveal that cochlear nerve damage precedes hair cell loss as a result of aging and noise exposure, and by not providing information about the cochlear nerve, audiograms actually reach the ear. It suggested that the full extent of the damage was not assessed.

Building a model for predicting cochlear nerve injury

In this study, the Maison and his team used a speech intelligibility curve to predict an individual’s speech score based on audiograms. Next, we measured the difference between the predicted word recognition score and the score obtained during the patient’s hearing assessment.

The Maison explained that the difference between the predicted score and the measured score reflects a lack of intelligibility, as the list of words was presented at a level well above the patient’s hearing threshold (audibility is not an issue).

After considering many factors, including cognitive impairment that may be associated with aging, researchers argued that the magnitude of these discrepancies reflected the amount of cochlear nerve damage or hidden deafness. .. Next, we applied measurements of nerve loss from existing histopathological data from the human temporal bone to build a predictive model based on standard hearing tests.

The findings confirmed an association between lower speech scores and more cochlear nerve injury. For example, the worst score was found in patients with Meniere’s disease. This is consistent with studies of the temporal bone showing a dramatic loss of cochlear nerve fibers. On the other hand, patients with conductive and drug-induced and normal age-related hearing loss (the patients with the least amount of cochlear nerve injury) showed only moderate or slight differences.

Changing the Perspective of Hidden Deafness Research

According to the World Health Organization, more than 1.5 billion people live with some degree of deafness. Some of these individuals may not be eligible for traditional hearing aids, especially if they have mild to moderate high frequency deafness. Knowing the extent of nerve damage should inform the clinician of the best way to address the patient’s communication needs and provide appropriate intervention other than the use of effective communication strategies.

By identifying which patients are most likely to have more cochlear nerve injuries, Maison said this model will help clinicians assess the effectiveness of traditional and new sound amplification products. thinking about. Researchers also want to introduce a new hearing test protocol to further refine the model and provide better intervention by assessing word performance scores in a noisy environment rather than a quiet environment. ..

Co-authors of this study include Kelsie J. Grant, Aravindakshan Parthasarathy, Viacheslav Vasilkov, Benjamin Caswell-Midwinter, Maria E. Freitas, Daniel B. Polley, M. Includes Charles Liberman and Victor De Gruttola.

This study was supported by the National Institute of Health (NIDCD P50-DC015857).

Revised from the news release of Mass Eye and Year.