Tinnitus may be linked to ‘hidden hearing loss’ missed on common tests, study suggests - NBC News

Scientists know that ringing in the ears, or tinnitus, is associated with hearing loss, aging, head or neck injuries, and exposure to loud noises. But what's actually happening in the body to cause it is less understood.

New research published Thursday in the journal Scientific Reports supports a theory that an underlying cause of tinnitus may be similar to phantom limb syndrome — a condition in which people experience pain in limbs they no longer have. 

"So the idea is, OK, I lost some hearing, my brain no longer receives some auditory information," said the senior author of the study, Stéphane Maison, a clinical audiologist at Mass Eye and Ear in Boston. The brain then tries to compensate for the hearing loss by increasing its activity, and "as a result, you start to hear a noise that's not there," he said. 

This understanding of tinnitus has received pushback in the scientific community, Maison said, because it assumes a patient with tinnitus already has hearing loss. However, many people with tinnitus can still perform normally on commonly administered hearing tests, he said. Such evaluations, called pure tone tests, often require patients to raise their hands when they hear beeps to measure the quietest sounds they can detect at different pitches. 

Maison said the study's findings reveal that the pure tone test assesses nerves sensitive to softer sounds. It doesn't account for the "hidden" hearing loss caused by damage to auditory nerves in the inner ear that are sensitive to louder sounds. 

"We know now that the hearing test does not tell you the whole story," Maison said. 

The study involved 294 participants ages 18 to 72 who all performed normally on a pure tone test. The participants were divided into three groups: 201 adults who have never experienced tinnitus, 64 who've had temporary tinnitus and 29 experiencing constant tinnitus for at least six months. 

The researchers conducted a hearing loss test that involves placing electrodes in the participants' ear canals and on their scalps to measure activity in the inner ear auditory nerve and the brain in response to clicking sounds.

The results showed far less activity in the auditory nerve, as well as hyperactivity in the brainstem among participants with tinnitus compared to participants with "normal hearing," Maison said. That suggests patients with tinnitus could have damaged auditory nerves that no longer send signals to their brains, potentially resulting in brain activity that causes patients to hear sounds of ringing, buzzing or hissing, he said. 

As many as 15% of adults worldwide have tinnitus, according to the study.

"Anything that is being done to better understand what might cause tinnitus is an important step towards a cure," Maison said. 

Laura Hermann, an audiologist at Johns Hopkins Medicine in Baltimore who wasn't involved with the study, said the comparison to phantom limb syndrome was spot on. 

She noted that the study outlined alternative ways to measure the "hidden hearing loss" in the auditory nerve that is associated with tinnitus. One that could be implemented within audiology clinics is called electrocochleography, another test that similarly evaluates the inner ear's response to a sound, she said. 

"I thought that was very interesting, because that's something a lot of audiologists have the equipment to do," Hermann said. "So, you know, that would be potentially a very cool way of validating these people's complaints coming in."

People who suffer from debilitating tinnitus often struggle to sleep and feel anxious or depressed, according to the study. 

Though there is no cure for tinnitus, Aniruddha Deshpande, the chair of the department of speech-language-hearing sciences at Hofstra University in New York, said there are simple steps people can take to protect themselves and potentially prevent the condition.

"Anything that can cause hearing loss can actually lead to tinnitus, because the underlying pathophysiology might be similar," Deshpande said. "So commonsense precautions of preventing exposure to loud noises is something that we can all do."

Deshpande said the most common cause of hearing loss in recent years is listening to music with headphones or over speakers too loudly. Though more research needs to be done to establish an "objective" threshold of what's considered safe, Deshpande said, previous research suggests people should listen to their music at no louder than 50% of their phones' maximum volume. 

In environments where you can't control the sounds in your surroundings — like concerts, for instance — wearing earplugs or muffs can prevent damage, he said. 

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