What Is Hidden Hearing Loss?

Recent research investigating the causes of hearing loss from noise and aging has identified what is now being called “hidden hearing loss”—declines in hearing function that are not revealed by traditional audiograms, but whose symptoms can include difficulty hearing speech in noisy environments. Learn more about this newly described type of inner ear damage.

A groundbreaking 2009 study by Hearing Health Foundation board member Sharon Kujawa, Ph.D., and M. Charles Liberman, Ph.D., described that with age or noise exposure, the neural synapses that facilitate communication between the ears and the brain can degrade, affecting hearing even though audiogram results appear typical.

• Watch: Our April 2022 ”Revealing Hidden Hearing Loss” webinar with Sharon Kujawa, Ph.D.

What Do We Know So Far About Hidden Hearing Loss?

• According to Mass Eye and Ear/Harvard Medical School, where the Kujawa and Liberman research was conducted, “Noise and aging first damage the synapses, which connect the [cochlear sensory] hair cells to the nerve fibers and ultimately carry neural signals to the brain. This hearing damage is now known as cochlear synaptopathy. Since hair cell function is what audiograms measure, this synaptic loss is typically undocumented, inspiring the popular term ‘hidden hearing loss.’”

• Besides noise exposure and “normal” aging, ototoxic drugs (such as chemotherapy medications) can also cause hidden hearing loss.

• Another recent discovery is a connection between cochlear synaptopathy and sound deprivation. Stéphane Maison, Au.D., Ph.D., CCC-A, of Mass Eye and Ear, found a link between underuse of the ear (sound deprivation) and hidden hearing loss. As such, chronic ear infections, conductive hearing loss, and conditions that cause hearing loss in one ear may lead to nerve damage similar to that seen in cochlear synaptopathy.

• Damage to the cells that produce the myelin sheath protecting neuronal axons is also linked to hidden hearing loss, according to a 2017 paper coauthored by Guoqiang Wan, Ph.D., a 2014 Emerging Research Grants scientist. Autoimmune disorders such as Guillain-Barré syndrome are known to attack myelin.

• About 10 to 15 percent of the population is believed to have hidden hearing loss, according to research published in 2018 and 2020.

• In a paper published in Scientific Reports in November 2023, loss of auditory nerve fibers has been uncovered in patients with tinnitus. individuals who report tinnitus, which present as a ringing in the ears in more than one out of 10 adults worldwide, are experiencing auditory nerve loss that is not picked up by conventional hearing tests. By measuring the response of their auditory nerve and brainstem, Mass Eye and Ear researchers including Maison and 2018 ERG scientist David Jung, M.D., Ph.D., found that chronic tinnitus was not only associated with a loss of auditory nerve but that participants showed hyperactivity in the brainstem. The investigators aim to capitalize on recent work geared toward the regeneration of auditory nerve via the use of drugs called neurotrophins.

• Researchers are developing methods to test for hidden hearing loss, sometimes involving testing at higher frequencies and also speech-in-noise (SIN) assessments such as AzBio, BKB-SIN, QuickSIN, and SPIN-R. Maison coauthored a 2016 study that detected hidden hearing loss among college-age students with typical audiogram results, which may point to an effective method for detecting cochlear synaptopathy.

• As with all hearing loss there is no cure, but avoiding excess noise can protect your hearing. In the 2016 study above, students who regularly used hearing protection when exposed to loud sounds scored better on speech-in-noise assessments.

Updated December 2023.

#KeepListening and #LoveYourEars

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