Causes of Hearing Loss

hearing-loss-issues

With all of the extraordinary medical advances of the past few decades, one might reasonably expect that medical professionals would be able to enumerate the causes of deafness. It’s true that they can recite a long list of things that can cause deafness. But it’s also surprising how often they are unable to identify the specific cause of a specific person’s deafness.

Research is continuing in this area, and progress is being made. In the near future, today’s common story that no one knows why a particular person is deaf may be a thing of the past. In the meantime, here is some information on some of the causes of deafness.

There are basically two types of deafness. One is caused by problems with the sound reaching the inner ear. Since the sound travels there via conduction, this is called conductive hearing loss.  It’s the far less common mechanism of hearing loss.

Much more common is sensorineural hearing loss. This is often called nerve deafness, but this is a misnomer, because the auditory nerve is almost never the cause. The problem is usually in the hair cells of the cochlea. One of the most devastating and mysterious forms of sensorineural hearing loss is sudden hearing loss or sudden deafness!

So what causes sensorineural hearing loss? Well, lots of things, many of which we can’t do much about. One big thing that we can control is noise. Noise is the enemy of hearing, and people are discovering that it doesn’t take as much noise as previously thought to cause temporary or permanent hearing loss. Here’s a bunch of information on Noise Induced Hearing Loss (NIHL).

Another surprisingly common cause of hearing loss is ototoxicity – the ability of drugs and medications to cause hearing loss.

June 2000 – Scientists have recently discovered a chemical that not only is crucial to the hearing process, but might also have profound impact on unrelated aspects of science.

June 2000 – Everyone knows that aging causes hearing loss, right? Just look around and notice all the older people who have hearing loss. It’s obvious that aging is the cause. It may be obvious, but is it true?

March 2005 – Scientists have recently discovered that hearing loss in older folks may have more to do with the brain than the ears!

June 2005 – Do airbags cause hearing loss?

July 2005 – It’s well established that genetic mutations cause a large portion of hearing loss cases; now scientists have found that other mutations can exacerbate the effects of the original mutations!

January 2006 – We all know that exposure to loud noise can cause sensorineural hearing loss. Now there’s evidence that it can cause acoustic neuromas, as well! Here’s the story!

January 2006 – Platinum cancer drugs tied to hearing loss in kids

January 2006 – Genetics and Hearing Loss: An Overview

February 2006 – When hearing is lost in the brain

March 2006 – Tumor growth related to exposure to noise

March 2006 – A recent Mayo Clinic study contradicts a previous study indicating that arthritis increases the risk of hearing loss.

March 2006 – Seeking the right amount of sound in the fury of combat

March 2006 – Scientists at the University of Michigan report less acoustic neuroma surgery that’s less damaging to hearing.

March 2006 – Dim view of aging linked to hearing loss

April 2006 – Can air bag deployment damage auditory function?

April 2006 – The presence of carbon monoxide seems to intensify hearing loss due to noise.

May 2006 – Aspirin Can Prevent Hearing Loss from Ototoxic Medication

May 2006 – Drinking red wine may help prevent deafness

May 2006 – Genetic cause of hearing loss in aging

May 2006 – Inner Ear May Take Beating From High-Impact Aerobics

August 2006 – Protein Tied to Usher Syndrome May Be Hearing’s “Missing Link”

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Do Airbags Cause Hearing Loss?

Most of you know that this newsletter has a companion website called Hearing Loss Web (http://www.hearinglossweb.com) One of the features of our website is a reader forum (http://www.hearinglossweb.com/discus), where people can exchange ideas about a variety of hearing loss topics. One of the topics that I found especially interesting was an exchange about air bags damaging hearing.

It began with a post from a young person who said (in part):

“Last week I was involved in what should have been a minor car accident. I wasn’t paying attention and ‘gently’ hit the car in front of me, which was stopped for a light.

“What happened next was terrifying. The inside of the car seemed to explode in a deafening roar. I had an unimaginable pain in both ears and considerable bleeding from my ear canals. I also had a very loud ringing and was virtually deaf.

“I was taken to the hospital where it was quickly determined that my eardrums had ruptured. I was referred to an ENT who said they should heal in 2-3 weeks but possibly with some scar tissue that would affect my ability to hear low sounds. As for the ringing, he said that could be permanent. He also said I had suffered inner ear damage that would affect my high frequency hearing although he said it was hard to tell how much. He concluded by saying I would need to face life ‘hearing impaired’ and may need to look at hearing aids.

“I just can’t believe this. What has our government done in requiring air bags that leave passengers deafened from minor accidents. I have always protected my hearing and never would have thought about going to loud concerts or auto races without effective ear protection. I’m only 22 and I can barely hear conversation in a quiet room. With background noise, I am almost deaf.”

The next few posts were from people who had similar experiences. Some reported that their hearing had returned to near normal, while others reported that their hearing had not.

Then a practicing ENT replied, stating that he has treated several folks for airbag-related conditions. He posted the following information:

“This is a big problem that needs concerted attention. I’m a practicing ENT who has treated a number of patients with air bag induced ear problems.

“I’d like to outline the facts as I see them. When an airbag is deployed, there is a loud “explosion” caused by the rapid escape of high pressure air. This is what gives the protection the air bag is designed for. Sound levels for this deployment have been extensively studied and generally will not cause permanent hearing damage in most cases. The noise is hazardous, but most of us will not experience more than 1 or 2 air bag deployments in a lifetime. Serious ear injury is likely to only occur if the person’s ear is right next to the airbag when it goes off. This is almost impossible for the driver but can occur for the passenger. For most people, the impact of an airbag will be a TSS that may cause several hours of ringing and hearing loss.

“The problem that hasn’t really been studied is the associated concussion that will occur in the car. The magnitude of this will be determined by the interior volume of the car, the number of air bags deployed, and whether windows are open or shut.

“Small cars, with closed windows, are clearly the worst. The other factor is the physical size of a person’s ear canals. People with small or average ear canals (or the opening to the ear canal) will have the impact of the concussion moderated. For people with large or extra large canals, the full force of the concussion will strike their eardrums, sometimes with catastrophic results. Eardrums can be ruptured, the delicate bones of the middle ear can be dislocated, and major inner ear damage can occur. I have treated over 10 patients that experienced this level of injury. All suffered some degree of permanent hearing loss. For reasons I can’t explain, 9 of them were women. I believe women, in general, are more susceptible to ear damage than men.”

A second ENT then replied, stating that he believes that the number of people whose hearing is damaged by airbags is in the thousands. He believes that cars need to be designed with built-in concussion relief, so the concussion effects described above do not occur. He also thinks that airbag sensitivities should be adjusted so that they are not deployed in a fender bender. He points out that a bloody nose or chipped tooth is preferable to a lifetime of hearing loss.

He also proposes a (somewhat tedious) partial solution. He suggests that people pack cotton very loosely in the openings of their ear canals, stating that this will not affect hearing, but will effectively moderate airbag concussion.

Having read all this, I’m surprised that we haven’t heard more about the dangers that airbags pose to hearing. It does sound like a serious problem that needs to be addressed. Ideas?

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‘Modifier Gene’ Makes Some Hearing Loss More Severe

July 2005

Editor: Scientists currently believe that about half of all cases of congenital or childhood-onset hearing loss are due to genetic mutations. Now they have verified that additional mutations can intensify the hearing loss caused by other mutations. Here’s the press release from the National Institute on Deafness and Other Communication Disorders (NIDCD).

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Scientists have identified a genetic mutation in humans that affects the severity of hearing loss caused by a mutation of another gene. National Institute on Deafness and Other Communication Disorders (NIDCD) scientists Drs. Julie Schultz and Andrew Griffith and co-authors at NIH* and the Mayo Clinic Foundation reported their findings in the April 14 issue of The New England Journal of Medicine.

Genetic mutations are estimated to cause at least one half of all cases of congenital or childhood-onset hearing loss. Individual variations in the severity of hearing loss are common and typically attributed to environmental factors and modifier genes – genes that alter the clinical expression of a mutation in another gene.

In the current study, five adult siblings from the same family were found to possess a mutant form of the gene that encodes for the protein cadherin 23, which is required for the development of hair cells in the inner ear. However, the degree of hearing loss among the siblings varied. While three of the five individuals had severe to profound deafness, the other two had hearing loss only in the higher frequencies. This variability suggested the action of a modifier gene.

NIDCD scientists, led by Drs. Thomas Friedman and Konrad Noben-Trauth, had previously discovered that mutations of the cadherin 23 gene cause hearing loss in humans and mice. Dr. Noben-Trauth and his co-workers had also shown that alterations of another gene, ATP2B2, can affect the severity of hearing loss caused by a cadherin 23 mutant gene in mice. ATP2B2 encodes for a key cellular protein, known as a plasma-membrane calcium pump, that is thought to be important for regulating calcium concentrations both around and within hair bundles of hair cells. On the outside of the hair bundle, calcium is required to maintain the correct structure of the hair bundles and on the inside it may act as an important signaling or regulatory molecule.

In this study, Dr. Schultz and her co-workers found that a mutant form of the human ATP2B2 gene, called V586M, accounted for the more severe hearing loss in the siblings who were profoundly deaf. The two siblings with better hearing were found to have normal copies of the gene. About 1 in 20 Caucasians are carriers of V568M.

Although V568M does not cause hearing loss, the current findings suggest that V568M may exacerbate hearing loss caused by environmental factors or other genetic influences. Further research is needed to determine the role of V568M and other mutations of the calcium pump in hearing loss associated with advanced age, exposure to loud noise, and mutations in other deafness genes.
*This research was also supported by the National Heart, Lung, and Blood Institute, another component of the National Institutes of Health.

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Platinum cancer drugs tied to hearing loss in kids

January 2006

Hearing loss appears to be a significant and under-reported side effect of platinum-based drugs used to treat a variety of childhood cancers, according to researchers. As senior investigator Dr. Edward A. Neuwelt told Reuters Health, so-called “mild” hearing loss “has major impact on academic and social development in kids, is very common after platinum chemotherapy, and may be prevented using” drugs called “thiol oto-protectants” that do not compromise the anti-cancer effects of the chemotherapy. Full Story

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Genetics and Hearing Loss: An Overview

January 2006

Knowing the exact cause of a child’s hearing loss can assist clinicians and parents in making decisions regarding treatment and educational options. It may surprise some parents to know that more than half of all children who are born deaf or who become deaf very early in life have a genetic cause for their hearing loss. In fact, recent  studies have revealed that approximately 50-60% of moderate to profound, congenital, or early-onset hearing loss is genetic. The remaining 40-50% of hearing loss is due to non-genetic effects, such as maternal infection (CMV or rubella), prematurity, postnata infection (meningitis, otitis media), ototoxic drugs, or acoustic/ cranial trauma.  Full Story

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When hearing is lost in the brain

February 2006

Age-related hearing loss is not just a case of the ears losing their capability. The ability of the brain to process sound is weakened as well. Modern digital hearing aids with directional microphones may solve some of these problems. The ears are still crucial for hearing, but preliminary studies in mice indicate that a decrease in certain processes in the brain may make it harder to filter out unimportant sounds. “Traditionally, scientists studying hearing problems started looking at the ear. But we are finding patients with normal ears who still have trouble understanding a conversation. There are many people who have good inner ears who just don’t hear well. That’s because their brains are aging,” said Dr. Robert D. Frisina of the University of Rochester Medical CenterFull Story

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Tumor growth related to exposure to noise

March 2006

The eighth cranial nerve has two branches, one that is responsible for balance and one that is responsible for hearing sensitivity. An acoustic neuroma is a non-cancerous tumor that grows on the eighth cranial nerve. The tumor typically grows very slowly and affects only one ear. Symptoms are not generally noticed until the tumor is large enough to puts pressure on nerves, causing the symptoms, including hearing loss, tinnitus, and facial weakness or numbness on the affected side, as well as dizziness or balance problems.   Full Story

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Seeking the right amount of sound in the fury of combat

March 2006

Modern combat is almost always noisy, but it was especially so in the Iraqi city of Fallujah in November 2004, when U.S. forces engaged insurgents in vicious house-to-house – often room-to-room – fighting. The reverberation of gunfire and explosions within concrete walls was so loud at times that “someone screaming in your ear could barely reach you,” said Jesse Grapes . . . Alarmed by the Fallujah experience, the corps revised its regulations last November to require that every Marine – “especially forward-deployed Marines in combat environments” – be issued Combat Arms Earplugs, trained in how to use them and required to carry them.  Full Story

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Dim view of aging linked to hearing loss

March 2006

Older adults who harbor negative stereotypes about aging may have a more rapid decline in their hearing, a new study suggests. Researchers at Yale University found that among older men and women, between 70 and 96 years old, those who held to the stereotypes of older adults as “frail” and “senile” showed a greater decline in hearing over the next three years. The link was independent of a number of factors in hearing loss, including age, physical health and depression. The effect was seen even in study participants who had “perfect scores” on hearing tests at the study’s start, lead study author Becca R. Levy told Reuters Health.  

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Can air bag deployment damage auditory function?

April 2006

On Monday, June 6, 2005, Lisa wrote the following on the Hearing Loss Web Forum under the topic of  “Air Bags Ruined My Hearing:”

“Last week I was involved in what should have been a minor car accident. I wasn’t paying attention and ‘gently’ hit the car in front of me stopped for a light. What happened next was terrifying. The inside of the car seemed to explode in a deafening roar. I had an unimaginable pain in both ears and considerable bleeding from my ear canals. I also had a very loud ringing and was virtually deaf.”  

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Drinking red wine may help prevent deafness

Age-related deafness, and hearing loss caused by loud noise, may be reduced by the antioxidants in red wine, green tea and aspirin, it was claimed yesterday. The compounds they contain could help protect the delicate hairs of the inner ear that are vital to hearing, new research suggests. Destructive chemical agents called oxygen-free radicals, produced by normal cellular processes and in response to loud noise and exposure to powerful antibiotics, can damage the hairs. But antioxidants such as resveratrol, found in red wine and green tea, and salicylate, the active ingredient in aspirin, should be able to neutralise them.   

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Genetic cause of hearing loss in aging

May 2006

Editor: Scientists have found many genes are implicated in hearing loss fairly early in life. Now it seems that they’ve found one that is related to late-onset hearing loss. Here’s the report from Indiana University.

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Researchers at Indiana University School of Medicine have taken a step toward understanding the genetics that make people more susceptible to the loss of hearing as they age. In a study of 50 pairs of fraternal twins with hearing loss, the scientists uncovered evidence linking the hearing loss to a particular region of DNA that previously was tied to a hereditary form of progressive deafness that begins much earlier in life.

The work is believed to be the first genomic screening in search of genes associated with hearing loss using a sample of elderly people drawn from the general population. The 50 sets of twins were drawn from a group of twins who are veterans of World War II and the Korean War.

The results suggest “that this region may contain an important locus for hearing loss in the general population,” said Terry E. Reed, Ph.D., professor of medical and molecular genetics at the IU School of Medicine.

The region of DNA identified by the IU study, a section of chromosome 3 named DFNA18, was implicated in a 2001 study of hereditary deafness in a large German family. It’s possible the two studies are pointing to the same gene or genes, with variation in the genes resulting in differences in susceptibility to hearing loss, Dr. Reed said.

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Inner Ear May Take Beating From High-Impact Aerobics

May 2006

PEOPLE who engage in demanding physical activities might expect to suffer occasional injuries to the body parts directly involved. But few devotees of high-impact aerobics are likely to guess that their jumping and bouncing to music could damage their inner ears, causing symptoms like persistent vertigo, dizziness, imbalance, motion sickness, ringing or fullness in the ear and high-frequency hearing loss. Yet just such a syndrome has been identified in a group of 30 otherwise healthy women in the Westchester County area of New York who regularly do high-impact aerobics, which involves a lot of bouncing up and down, often with both feet off the ground at once.

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