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Sudden Sensorineural Hearing Loss: Hard to Define, Hard to Treat

From: ENT Today, December 2006

by Matt Brown

TORONTO-Sudden sensorineural hearing loss (SSHL) has stumped otolaryngologists for decades. Despite much attention, even a definitive definition of the malady escapes researchers, making successful therapies even harder to uncover.

According to the National Institutes of Health (NIH), approximately 4000 new cases of SSHL occur each year in the United States. It can affect anyone, but for unknown reasons it happens most often to people between the ages of 30 and 60. In an effort to spur discussion and a possible movement toward consensus, an international panel gathered to examine the epidemiology of SSHL and discuss traditional treatment modalities at the recent American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) annual meeting here.The experts also wheeled out some of the more promising research and cutting-edge treatment modalities available.

Figure. SSHL occurs most often in people between ages 30 and 60; a number of causal ideologies have been proposed.
click for large version
Figure. SSHL occurs most often in people between ages 30 and 60; a number of causal ideologies have been proposed.

What Is SSHL?

While SSHL characterizations remain varied, the NIH defines the condition as an idiopathic hearing loss of sensorineural origin, greater than 30 dB in three contiguous frequencies that occurs in less than three days. Session moderator Commander Michael E. Hoffer, MD, of the Naval Medical Center in San Diego, said that, in addition, the root causes of SSHL could be broken into two separate types-idiopathic and direct effect.

Idiopathic represents all of the presumed causes that we can come up with, he said. Direct effect deals with things we know caused the hearing loss-largely loud noise, trauma, or toxins. Basically, someone gets blown up, they get a hearing loss and we know it was direct effect.

In the idiopathic camp, there are a number of possible causal ideologies at work-vascular, viral, genetic, lifestyle, and disease-related causes, Dr. Hoffer said. The vascular hypothesis comes from a Japanese study showing subjects had an increased incidence of SSHL when switching from a traditionally Japanese diet to an American diet.This showed promise at the time, Dr. Hoffer said, but when combined with other, similar research, it became clear that genetic causes were at play. He also said viral ideology research is conflicting and cannot be reproduced, but that he is still convinced there has to be some kind of infectious variable at work.

There is a strong link to the genetic and lifestyle ideologies and a much weaker one to viral and vascular, Dr. Hoffer said.

With regard to incidence and prevalence of direct effect SSHL, he said both were hard to quantify because the data are such that a reliable denominator is not available.

What percentage of the given population is affected and how exactly were those people affected? Dr. Hoffer said. We don't know those things. No denominator and a very poor numerator make this very hard to calculate.

Regardless of the who, what, and where, with America at war in Iraq, the number of SSHL cases Dr.Hoffer is seeing continues to rise.He said hearing loss from noise accounts for one in five hearing losses severe enough to be reported, and that one-quarter (24.9%) of servicemen and women report a hearing loss when they leave active duty.

Sixty to 90 percent of those soldiers in Iraq that report being close to a big explosion report hearing loss, he said.We did a series of studies…one showing that after a two-week rifle and weapons training evolution 11 percent of the population walked out with hearing loss they didn't have before they started.

Another study showed new-onset hearing loss after three weeks with the same percentages. That 10 to 11 percent number just keeps coming up and…it all goes back to genetics.

Lorne S. Parnes, MD, of the University of Western Ontario in London, Canada, talked about his research into the Englishlanguage literature comparing the efficacy of oral steroids to antiviral medications. While the data in the studies that made the cut were thin-only 183 total subjects participated in the 17 studies selected-Dr. Parnes said he came to the conclusion that although oral steroids are the standard-of- care therapy used in most otolaryngology practices, there is no real proof as to the therapy's efficacy versus placebo.

There was no significant positive effect shown with oral steroids…and they do not seem to be the gold standard they are advertised to be, he said.There was also no positive effect seen when using oral steroids over other treatments.

On the other hand, Dr. Parnes said, the work he did on animals using transtympanic medical therapy has shown promise.

The research team hypothesized first that corticosteroids could permeate from the middle ear through the round window membrane into the inner ear fluids. Second, they believed that administering the drugs this way would result in higher inner ear fluid drug concentrations and lower systemic blood concentrations as compared with systemic administration.

The study concluded that all three steroids could permeate the blood barriers and…the intratympanic route provides the highest drug levels, Dr. Parnes said.Half of the 26 patients were treated right away…and we have concluded that the treatment needs to be done within 30 days of an arbitrary hearing loss or it will not be effective. For those that were treated early, you can see statistically significant improvement in all of the measured parameters for all of the patients.

This was the first study to examine intratympanic steroids as the primary treatment for idiopathic sudden deafness, although there had been prior reports in the literature using intratympanic steroids as salvage treatment when oral steroids didn't work. The key here, he said, was that data showed a statistically significant difference in overall hearing after treatment and improved treatment in patients treated after 10 days.

We admit this was a small study with a limited sample size of 26 patients, and admit there was a lack of a control arm, but we were able to make this direct compairision in patients treated within 10 days and those treated after 10 days, Dr. Parnes said.We need more data and a bigger study. But it shows that within 10 days this is a safe and possibly effective treatment for SSHL and a multicenter study is needed to define and outline the role of this treatment.

Using Evidence-Based Medicine

Harvard's Steven D. Rauch, MD, continued from there, talking about his National Institute on Deafness and Other Communication Disorders (NIDCD)-sponsored trial and the importance of relying on science instead of faith.

The era of evidence-based medicine is hurtling toward us and in most other specialties it is already there and we are behind the curve in that regard, he said. Faithbased medicine isn't going to cut it, and just because you believe something is the right treatment just isn't enough. We're in a special window of time right now where there is a great billing code for intratympanic drug injection, but not a lot of evidence of its efficacy exists and that window is going to close unless there really is evidence that it's a good treatment.

Dr. Rauch, whose own study won't be complete until 2009, preached caution where thereapies are concerned.

None of us are satisfied with the efficacy of oral steroids for hearing loss, he said. That is why intratympanic therapy is here. It uses the 'If some is good, more is better' philosophy. But that is really simple thinking and it may not be the correct thinking.

Dr. Rauch said his current study is comparing the efficacy of intratympanic injections and oral administration head-to-head.

This is a noninferiority study,he said. If one drug [oral steroids] is accepted, you can compare the other [intratympanic] and say that it is at least as good. Can we say that intratympanic therapy is at least as good as oral? I'll tell you in 2009.

Developments in Drug Therapy

Commander Ben J. Balough, MD, Chief of Otolaryngology at the Naval Medical Center, San Diego, and Michael Seidman, MD, of the Henry Ford Health System in Detroit, ended the session talking about the newest, cutting-edge drugs.

Many things are being used to treat sudden hearing loss-but I am most interested in antiapoptic agents…and gene therapy,Dr. Balough said.From a hair cell protection standpoint, it is interesting that you can protect hair cells not only before damage is accrued but even rescue those cells afterwards. It's even been shown that simply taking aspirin can be otoprotective.

Dr. Balough said that the investigational otoprotective drug AM-111 was used to treat cochlear stress in guinea pigs in one of his studies and showed good results.

They have even enrolled people at a rock concert in Germany, dripping [AM-111] into their ears before the show, he said.It showed protective effects afterward.

Dr. Seidman said that while surgeons do know how noise affects the biochemical pathways and how those paths can be manipulated, the medical industry doesn't know how that process relates to SSHL. Referencing the same 10% to 11% figures quoted by Dr. Hoffer, Dr. Seidman commented that therapies are being tested that have shown success regrowing outer ear hair cells and saving those that are stunned.

We can replenish antioxidants, stabilize cell membranes, inhibit apoptosis, and upregulate protective enzymes-glutathion replenishment, stabilize membranes with acetyl-L-carnitine (ALCAR), inhibit the apoptosis with the AM-111, and upregulate with various other compounds, Dr. Seidman said.

Whatever the therapy, the number of SSHL cases is growing and science needs to answer the call, Dr. Hoffer said.

Whatever the cause, this is a debilitating and increasingly frequent medical issue, he said. The causes of sudden sensorineural hearing loss have been identified better than they had been previously, but now what do we do about it?

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