Sudden Hearing Loss (SHL, SSHL)

© March 2001 (revised June 2007) by Neil Bauman, Ph.D.

Question: My mother suddenly lost her hearing. She never had any known ear illnesses before. What could cause this?—S. M.

Answer: Good question! Few things are so baffling (and scary) as waking up one day and finding your hearing is gone. Immediately you want to know what caused it, and more to the point, can anything be done to bring your hearing back.

Ear specialists tell us that sudden sensorineural (inner ear) hearing loss is one of the most perplexing and controversial unsolved mysteries about our ears. Since even they can't agree among themselves what causes it, nor how to treat it, no wonder you are baffled. Here's the latest on this subject.

There are two basic kinds of hearing loss. If the hearing loss occurs in the middle ear, we call it a conductive loss. If it occurs in the inner ear, auditory nerve or brain, we call it a sensorineural hearing loss. (The old term was "nerve deafness.")

Sudden Conductive Hearing Losses

Sudden conductive hearing losses are relatively easy to diagnose and fix. The most common example would be the ubiquitous head cold. It may result in fluid build up/infection in your middle ears. Because the little bones in your middle ears can't move freely in the fluid like they do in air, you don't hear as well. You likely also feel pressure in your ears or your ears feel "plugged up." This condition normally affects both ears at the same time. Fortunately, when this fluid drains out your Eustachian tubes (which may take up to several weeks), your hearing returns to normal. This kind of hearing loss is quite common, especially in younger children, but is not normally a serious problem and is certainly not a medical emergency.

More serious could be a blow to your head, or a sudden loud sound like an explosion that could dislocate/break the tiny bones in your middle ear. You need to go to your ear specialist at once. Your ear specialist can often repair this damage through surgery and your hearing returns to normal or near normal again.

Sudden Sensorineural Hearing Loss (SSHL).

Sudden sensorineural hearing losses (SSHL) are medical emergencies. You need to see your ear specialist (preferably an otologist or neurotologist) immediately (not your family doctor—he is not qualified and it wastes precious time you don't have).

By definition, you have SSHL if you have a hearing loss that occurs within three days (often within minutes or an hour or two) and your hearing loss is greater than 30 dB over three adjacent octaves (test frequencies) as shown on your audiogram.

About one-third of the people with SSHL discover their hearing loss when they wake up in the morning. They go to bed with normal hearing, and in the morning they realize they are deaf in one or both ears! Fortunately, SSHL only affects both ears about 2-4% of the time. Other people discover their loss when they go to use the phone and realize they can't hear the phone with one ear any more.

SSHL may be almost instantaneous. In such cases, you may notice a loud sound or a loud "pop" just before your hearing disappears. You will also experience dizziness or vertigo 50% of the time and tinnitus (ringing in your ears) about 70% of the time. Incidentally, the intensity of your vertigo often roughly corresponds to the degree of your hearing loss. You might also have a feeling of fullness in your ear(s) and a headache.

How common is SSHL? It varies, but the average seems to be that about one person in 10,000 experiences SSHL in any given year.

Causes of SSHL

SSHL is not a disease as such, but rather is the end result of damage to the auditory system from various causes. The sudden hearing loss is a symptom indicating that something has gone horribly wrong in your ears somewhere.

It's rather interesting that although doctors have identified over 100 causes of SSHL, they can only identify the specific cause about 15% of the time. The rest of the time they call it "idiopathic"-of unknown cause. This is where all the mystery and controversy comes in.

Here are some of the causes of SSHL.

There are many drugs that can damage your ears (ototoxic drugs). Certain antibiotics, certain diuretics and certain anti-cancer drugs are particularly damaging to your hearing and can result in SSHL.

About 10% of the people getting Meniere's Disease experience SSHL. Perilymphatic leaks (perilymph is one of the two inner ear fluids) can occur if either the oval (resulting in vertigo) or round window of the cochlea ruptures. These perilymphatic fistulas are what we think happens in cases of Meniere's disease, from strenuous physical activity, straining or sudden changes in barometric pressure such as flying or scuba diving. Early surgical intervention to seal the leak may prevent further hearing loss and may restore some of the lost hearing.

About 10-15% of the people with an acoustic neuroma develop SSHL. (Acoustic neuromas are benign slow-growing tumors on the auditory nerve. Since they grow slowly, normally hearing loss is gradual.) Also other tumors such as cerebellopontine angle tumors can cause SSHL.

Trauma such as head injuries and temporal bone fractures can cause SSHL.

Circulatory problems feeding blood to your ears can cause SSHL. For example, lack of blood flow to your inner ears can result in permanent hearing loss in just 60 seconds. This could result from a partial or complete blood clot (a mini-stroke in your inner ear). SSHL could also result if your blood is too "thick" (the fancy name is hyperviscosity). You could get SSHL if your blood is too thin (from taking blood thinners like heparin), which causes internal bleeding in your inner ears; if the tiny blood vessels in your inner ears are destroyed (polyarteritis nodosa); if your blood clots too much or too fast; or if you have poor circulation from vascular sludge.

SSHL can result from deformed inner ear conditions such as Mondini syndrome, large vestibular aqueduct syndrome and labyrinthitis ossificans.

SSHL can result from immunologic diseases such as Cogan's syndrome and Lupus and from various autoimmune conditions. An autoimmune condition that affects the cochlea is called Autoimmune Inner Ear Disease (AIED).

Viral infections are now thought to be the most common cause of SSHL. Recent studies show that this viral activity may be sub-clinical-meaning that it is not detected with standard clinical tests. According to one recent study, Herpes Simplex virus Type 1 (HSV-1) seems to be the most likely culprit. In animals inoculated in their inner ears with HSV-1, all the animals rapidly lost their hearing.

Other viruses thought to cause SSHL include adenovirus, cytomegalovirus (CMV), infectious mononucleosis, influenza, measles, mumps, parainfluenza, rubella and rubeola.

Miscellaneous causes of SSHL include endocrine disorders such as hypothyroidism and diabetes, exposure to pesticides, certain snake bites, encephalitis, leukemia, meningitis, multiple sclerosis and syphilis.

Treatment of SSHL

If you have a clear history of SSHL associated with diving, straining, altitude change (flying) or recent ear surgery, see your ear specialist immediately as surgery is often necessary to fix the problem.

If all obvious causes of SSHL are ruled out and your doctor calls it idiopathic SSHL, here are some things you should know.

About one third of the people with idiopathic SSHL recover completely without any treatment. Another third recover some or most of their hearing with treatment. The remaining third don't recover any hearing whether treated or not.

You want to be in the first group for sure, but you don't have a choice. Here is how to realistically tell what will likely happen in your case. Whether you recover your hearing to a large extent seems to depend on these factors. (These factors are not engraved in stone. If you happen to be in the "wrong" group, don't lose hope. Your hearing may come back-just don't expect it to. If it does, you can be pleasantly surprised.)

If you had a mild to moderate hearing loss in the mid frequencies (1,000-2,000Hz), you hearing will likely come back on its own within two weeks-whether you have any treatment or not. In other words, current treatments don't work and are unnecessary.

If your hearing loss was profound (greater than 90 dB), you only have a 25% chance of getting your hearing back, regardless of the treatment you receive.

If your hearing loss was less than 90 dB and not limited to the mid-frequencies, then immediate treatment with steroids (within 10 days) has a 78% chance of restoring your hearing (or at least some of it). The only treatment that has proved effective (supported by double-blind trials) is corticosteroid treatment-usually Prednisone or Prednisolone. This generally works if you have a hearing loss in only one ear, your loss is a moderate loss across many frequencies and you are younger than 40.

Apparently this study was not entirely accurate since it was not randomized and thus may have produced exaggerated results. Furthermore, the study does not inform doctors what dose of steroids to use, nor at what time after treatment it expect improvement.¹

Note that at the present time, there is no truly successful therapy for people with SSHL because even after treatment, you still will likely have considerable hearing loss. In fact, some ear specialists choose not to treat sudden sensorineural hearing loss at all, citing spontaneous recovery rates of 32-70%.¹

Here are the various factors that seem to determine whether you will get your hearing back or not.

The severity of your hearing loss is inversely proportional to the rate of your recovery. This means that the milder your loss, the faster you will get your hearing back. Once recovery begins, it is likely to be rapid-in a matter of 7-10 days.

If you have vertigo, it tends to subside within one week and as a rule, all vestibular symptoms clear up within 6 weeks.

As a matter of interest, if you get tinnitus with your SSHL (about 70 to 85% do), it has no bearing on whether your hearing returns or not.

Studies indicate that the current practice doctors use—called the "shotgun" approach—giving steroids, vasodilators, diuretics, antihistamines, anticoagulants, carbogen, anti-virals, etc. and hoping that one or the other will do some good, was found to be no more effective than doing nothing at all! Only the steroids have been found effective in certain cases (described above).

No difference existed between people treated with antiviral plus steroids vs. placebo plus steroids, nor was there any difference between people treated with steroids vs. people treated with any other active treatment.¹

So although positive results have been reported favoring systemic steroids, steroids injected through the eardrum, magnesium, vitamin E and hyperbaric oxygen, there are no randomized, blinded studies supporting the efficacy of any of these treatments. Therefore, at this time "sudden sensorineural hearing loss remains a medical emergency without a scientific understanding of its cause or a rational approach to its treatment."¹

Understanding as much as you can about SSHL helps take the fear of the unknown away so that you can better cope with it. On a positive note, doctors are making rapid advances in understanding what goes on inside our ears. As a result, they may shortly discover new and better treatments for this condition.

References:

¹ Evidence lacking to guide treatment for sudden hearing loss. June 18, 2007. EurekALert.  http://www.eurekalert.org/pub_releases/2007-06/jaaj-elt061407.php reporting on article by Elizabeth Conlin and Lorne Parnes in the Archives of Otolaryngology Head and Neck Surgery June, 2007 (133:573-581, 582-586).