Researchers at the Massachusetts Eye and Ear Infirmary have found that tinnitus, which affects more than 10 percent of adults worldwide, is associated with imperceptible auditory nerve loss. Their research shows that even people with normal hearing tests can suffer from this hidden hearing loss, paving the way for new treatments focused on neuroregeneration.
A groundbreaking study from the Massachusetts Eye and Ear Infirmary links tinnitus to undetected damage to the auditory nerve, challenging previous beliefs and opening new avenues for treatment through auditory nerve regeneration.
More than one in 10 adults worldwide develop tinnitus, and people with tinnitus are experiencing damage to the auditory nerve that goes undetected by traditional hearing tests, according to a new study from Massachusetts Eye and Ear researchers. This work is part of a P50 grant awarded by the National Institutes of Health (NIH) to Massachusetts Eye and Ear researchers at the Eaton-Peabody Laboratory (EPL) for their research on cochlear synaptopathies, often referred to as "hidden hearing loss." The results of the study provide a better understanding of the origins of tinnitus and are published today (30 November) in the journal Scientific Reports.
The impact of tinnitus on quality of life
Senior author Stéphane F. Maison, MD (CCC-A), principal investigator at the Massachusetts Eye and Ear Department at Massachusetts General Brigham Hospital and clinical director of the Massachusetts Eye and Ear Tinnitus Clinic, said: "Tinnitus symptoms, in addition to causing persistent tinnitus or other sound distress to patients, can cause many patients to suffer from tinnitus. Disabling tinnitus, resulting in sleep deprivation, social isolation, anxiety and depression, adversely affecting work performance and significantly reducing their quality of life. Until we fully understand the mechanisms of tinnitus, we cannot cure tinnitus."
Many people with hearing loss experience buzzing, humming, ringing, or even roaring in their ears. These symptoms, known as tinnitus, have long been thought to be the result of poor adaptive plasticity in the brain. In other words, the brain attempts to compensate for the loss of hearing by increasing its activity, creating auditory hallucinations known as tinnitus. Until recently, this idea was questioned because some people with tinnitus have normal hearing test results.
However, the discovery of cochlear synaptopathy in 2009 by researchers at Massachusetts Eye and Otology gave this hypothesis a new lease of life, as evidence emerged that patients with normal hearing tests may have severe damage to their auditory nerves. In light of a paradigm shift in how researchers and clinicians view hearing loss, Mason and his team sought to determine whether this hidden damage was related to tinnitus symptoms in a group of people with normal hearing. By measuring responses in the auditory nerve and brain stem, the researchers found that not only was chronic tinnitus associated with auditory nerve loss, but the participants' brain stems also showed hyperactivity.
Searching for potential treatments for tinnitus
"Our work supports the idea that tinnitus may be caused by loss of the auditory nerve, including in people with normal hearing," Maison said.
As for future research directions, the researchers hope to use recent findings to promote auditory nerve regeneration by using drugs called neurotrophins.
One day, researchers may be able to bring the missing sounds back into the brain, perhaps combined with retraining to reduce their arousal, which will undoubtedly bring the hope of a cure closer to reality.