Idiopathic sudden sensorineural hearing loss (SSNHL), also known as sudden deafness, is defined as the onset of unexplained one-sided SNHL in less than 72 hours. It strikes an estimated 5-20/100,000 persons per year. This is approximately the same incidence as Meniere’s syndrome (15 per 100,000), and nearly as common as Bell’s Palsy (20-30 per 100,000).
This incidence of SSNHL is likely to be an underestimate as many who recover quickly will never seek medical attention. The average age of affected individuals is around 50 years but both younger and older people can develop this condition. There is equal sex distribution. Vestibular symptoms of dizziness, vertigo, or imbalance are present in about half of patients.
Research indicates a worse hearing prognosis with presence of vestibular dysfunction and/or with advancing age. All reports describing treatments indicated that earlier initiation of treatment was associated with better hearing outcome. Many patients, especially those with milder hearing loss, can experience some degree of spontaneous improvement, though rarely to normal. This condition is a true ear emergency since the chance of hearing recovery decreases with delay in treatment. There is a window of two to four weeks to get treated. If four weeks passes before treatment is started, there is little chance of any benefit. If treatment is started within the first two weeks after SSNHL onset, about 80 percent of patients show some improvement and some will even recover to normal.
Not all cases of sudden deafness are idiopathic. More than 50 different causes of sudden deafness have been described. “Idiopathic SSNHL” is the assigned diagnosis when no clear cause is known. Although many mechanisms have been proposed, the most popular theories to explain these cases invoke viral infection, inflammation or immune system problem, or impaired circulation. In fact, all of these mechanisms probably do occur. However, evidence supporting these theories is circumstantial. SSNHL is almost exclusively unilateral (one-sided) disease. Rare cases of bilateral sudden deafness are most often seen as a psychiatric “functional” hearing loss, or as a neurological event arising from malignant tumor growing along the dura lining the skull or from infection or inflammation of the brain or brain covering. Transient or temporary bilateral sudden sensorineural hearing loss may be seen from sudden drop in spinal fluid pressure during spinal tap. Approximately 99 percent of cases of typical unilateral sudden sensorineural hearing loss are idiopathic. The remaining 1 percent are predominantly due to “retrocochlear” disease, such as vestibular schwannoma (a.k.a. acoustic neuroma; a type of benign tumor), demyelinating disease (multiple sclerosis), or stroke.
SSNHL falls within a spectrum of idiopathic acute auditory and vestibular dysfunction. At one extreme is sudden onset of pure vertigo with no auditory symptoms. This is known as vestibular neuritis and is widely attributed to be a peripheral viral inflammation of the balance nerves. At the middle of the spectrum is the combined sudden loss of both hearing and balance known as labyrinthitis. The vertigo of such cases almost always resolves over some span of weeks to months (probably due to central compensation), but the hearing rarely recovers. Labyrinthitis is also believed to be viral. However, instead of viral damage to the vestibular nerve or its ganglion cells seen in vestibular neuritis, labyrinthitis is believed due to a process affecting the fluid spaces of the inner ear and thus involving both auditory and vestibular systems. The distinction of vestibular neuritis from labyrinthitis is based on hearing involvement – vestibular neuritis patients have normal hearing and labyrinthitis patients have sudden deafness along with their vertigo. Interestingly, the neurology literature tends to lump these conditions together as “neurolabyrinthitis.” At the auditory extreme of the spectrum is idiopathic SSNHL, sudden deafness with brief, mild, and transient vestibular symptoms, if any.
The critical diagnostic issue in SSNHL is determination that the hearing loss is indeed sensorineural. Sudden hearing loss is an extremely common symptom. It typically presents as a feeling of ear fullness. Anyone who has had wax impaction, water in the ear, ear congestion with a head cold or allergy, or Eustachian tube obstruction during airplane descent knows the sensation. What all these common causes of ear fullness share is that they produce conductive hearing loss. If an acute audiogram (hearing test) was performed in any of these cases, the bone-conducted hearing thresholds, which indicate sensitivity of the hearing nerves, would be normal but the air-conducted thresholds might be elevated. Idiopathic sudden sensorineural hearing loss produces an identical sensation of aural fullness but the audiogram shows a marked elevation in bone-conducted hearing thresholds (that is, a loss of nerve sensitivity).
Perhaps the greatest clinical problem in SSNHL is delay in diagnosis. Since the symptom of ear fullness is such a common and familiar one, most patients attribute it to wax impaction or congestion from upper respiratory illness or allergies. They may wait for days or weeks before seeking medical evaluation, and are then often treated symptomatically for a time before eventual referral to an otolaryngologist. Unfortunately, the window of opportunity for SSNHL treatment is no more than four weeks from onset of symptoms so a delay in diagnosis usually equates to a permanent hearing loss.
The most common chief complaint in SSNHL is aural fullness, followed by complaints of hearing loss and tinnitus. Aural fullness is a common and non-specific symptom. Many patients do not immediately associate it with hearing loss. Common non-otologic causes include temporomandibular joint (TMJ) dysfunction, general upper airway congestion from viral upper respiratory illness or environmental allergies, and musculoskeletal dysfunction of the upper neck, e.g. from degenerative joint disease, muscle strain and spasm, whiplash, cervical disc disease, or other acute or chronic neck injury. The first step in diagnosis is to determine if a patient’s complaint of aural fullness is due to hearing loss.
Hearing loss assessment is accomplished differently if it is conducted by telephone interview (e.g. by a clinic nurse) or if it is a face-to-face assessment. By phone, the simplest method is to ask the patient if their hearing is reduced. The patient can move the phone from ear to ear to check for hearing asymmetry. Alternatively they can be asked to crinkle a few hairs next to the ear on each side to see if there is a difference. If the hearing is determined to be asymmetric, the next critical determination is whether the loss is conductive or sensorineural. Acute conductive hearing loss is generally not an emergency, but acute SNHL absolutely is. A simple test can often make this distinction. The patient who reports acute unilateral hearing loss is instructed to hum out loud and is then asked which side hears the voice better. Conductive hearing loss will lateralize sound (seem louder) to the blocked ear, while a sensorineural loss will lateralize sound to the good ear. Thus, one can remember that “hearing the humming in the bad ear is good and hearing it in the good ear is bad.” In a face-to-face interview, hearing can also be assessed with whispered speech testing by very softly whispering simple words or numbers in each ear and asking the patient to repeat them out loud.
In all cases of suspected hearing loss examination by an Otolaryngologist is essential. They will inspect the ear canals and ear drums. If necessary, the ears will be cleaned to gain full view of the ear drums. It goes without saying, that if this cannot be accomplished by the Primary Care or Emergency Ward staff, Otolaryngology consultation is mandatory. Only about half of idiopathic SSNHL patients have vestibular symptoms. It is appropriate for your doctor to perform a focused neurological and balance examination to seek any indication of central or vestibular system dysfunction.
Audiometry (hearing testing). A complete audiogram is mandatory in all patients suspected of hearing loss or asymmetry and is strongly encouraged in any patient with new onset of ear symptoms or discomfort of any kind. A complete audiogram includes measurement of auditory thresholds for bone-conducted and air-conducted pure tones from 250 to 8000 Hz in both ears, and speech audiometry that measures the Word Recognition Score by having patients repeat single syllable words from standardized list when they are delivered to the patient via headphones at a comfortably loud listening level. Hearing threshold and speech audiometry assess the loudness and the clarity of hearing, respectively, and are analogous to the volume control and the tuner on a radio. In patients who have poor Word Recognition Scores the sound is like a radio station with poor reception – increasing the loudness does not improve the sound quality. SSNHL can affect loudness, clarity, or both. It can affect all frequencies (pitches) of hearing equally or it can affect just the high or low frequencies. The severity can be highly variable. The worse the hearing loss, the poorer the prognosis for recovery and, therefore, the greater the urgency to get on treatment.
Brain MRI. Since acute neurological problems such as tumor, stroke, or demyelination (MS) can cause sudden deafness, a gadolinium-enhanced MRI of the ear, skull, and brain is mandatory to rule-out these serious conditions. In patients who cannot have brain MRI alternatives include CT scanning and/or Auditory Brainstem Response (ABR; a.k.a. Brainstem Auditory Evoked Response, BAER or Brainstem Evoked Response, BSER) audiomtery. These are less sensitive than MRI but may still be useful. In patients who are able to have MRI, CT scan is inadequate to appropriately assess SSNHL patients. Since only 1 percent of SSNHL cases are due to these other neurological conditions, treatment should be started immediately even if there is a delay in obtaining appropriate imaging studies.
Standard treatment for SSNHL is a tapering course of oral corticosteroids (prednisone or methylprednisolone). Since research performed at the Massachusetts Eye and Ear Infirmary in 1980 for demonstrated the effectiveness of this treatment, it has been widely used. Treatment of SSNHL consists of a short burst of oral prednisone or methylprednisolone, followed by a taper over several days. Duration of therapy varies from site to site around the United States, but a typical treatment would be prednisone 60 mg/day for 14 days, followed by a five-day taper (50 mg, 40 mg, 30 mg, 20, mg, 10 mg). This oral treatment regimen was designed to strike a balance between giving enough prednisone to achieve benefit but without producing an unacceptably high level of side effects. In the last 15 years there has been increasing interest in giving the steroid treatment by direct injection through the ear drum. The hope was that the injection treatment would achieve higher drug concentration in the ear while minimizing steroid exposure to rest of the body. A recent large multicenter clinical trial showed conclusively that oral and intratympanic injection treatments are equally effective. Patients should discuss with their treating Otolaryngologist the pros and cons of using each (or both) of these treatments.
Response to steroid treatment follows a variable time course, but is generally better early in the course of therapy. Some patients exhibit a very rapid and substantial recovery of hearing within the first 48 - 72 hours. Others have no response for the first week or two of steroids and then continue to make improvement after the steroid taper is completed. The sooner a response is seen, the better the overall prognosis. Patients who get all the way to the end of their course of steroid treatment with no demonstrable benefit have a poor prognosis for further hearing recovery. However, many patients who begin to improve while on steroids may continue to do so for weeks or months thereafter. Approximately 80 percent of recovery is seen by the end of the two-week treatment, and a little more improvement may be seen in the following weeks. Patients who initiate oral steroid treatment more than four weeks after onset of their SSNHL have virtually no chance of oral steroid benefit.
A number of other treatments have been proposed for SSNHL. These include antiviral drugs, drugs to reduce blood clotting or increase circulation, hyperbaric oxygen treatments, or inhalation of gases to increase circulation. While there are theoretical reasons to consider each of these treatments, none of them has stood the test of time nor been shown to be more effective than oral steroids.
Since there is only a two to four week window of opportunity for treating SSNHL, it is essential to initiate therapy as soon as possible, even if a complete diagnostic work-up has not been completed. Ideally, an audiogram should be performed before starting treatment, but if it is performed within 24 - 48 hours, this an acceptable alternative. One should never postpone treatment for days or weeks to await results of imaging studies. Furthermore, spontaneous recovery or good response to treatment does not eliminate the need for imaging. Demyelinating disease can have a fluctuating course or transient response to steroids and it is not uncommon to observe acute enlargement of an acoustic neuroma tumor, perhaps from hemorrhage, that results in sudden sensorineural hearing loss that improves (with or without treatment) over a span of days or weeks.
After completion of treatment, SSNHL patients should have continued audiometric monitoring for one year. Retesting hearing at two months, six months, and 12 months after onset of SSNHL provides an opportunity to document the stability of any hearing recovery and to track the progress of adjunctive symptoms of tinnitus and aural fullness. It is especially important to monitor for signs of relapse in the affected ear or development of hearing loss in the opposite ear, both of which are unanticipated and would indicate need for re-evaluation.
There are three standard recommendations made to all monaural (i.e. only one “good” ear) patients: (1) Lifelong prohibition against scuba diving. There is a high incidence of ear injuries in recreational diving and the SSNHL patient has only one ear that should not be put at risk. It is even questionable whether an SSNHL patient who makes a full recovery should resume diving, since we do not know if the SSNHL creates permanent vulnerability in the affected ear. (2) Hearing conservation equipment in noise. Acoustic trauma is a risk we all face from loud music, power tools, yard equipment, etc. The patient who has only one good ear must be especially vigilant. Noise injury is not confined to construction workers and military combatants. There are plenty of weddings and social events where the DJ plays the music loud enough to harm hearing. Earplugs or earmuffs designed for noise protection are inexpensive, widely available, and very effective when used properly. (3) Otolaryngology evaluation within 24 hours for any new ear symptoms in the good ear. SSNHL does not appear to raise the risk of hearing loss or other problems in the opposite ear. However, since the opposite ear is the patient’s only normal ear, one must have a very low threshold for seeking assessment and care of any problem that arises.
Prompt SSNHL treatment with a tapering course of oral steroids is associated with hearing improvement in approximately 80 percent of patients. Virtually all published series have noted better outcome with earlier steroid treatment than in those whose treatment is delayed. SSNHL patients who regain hearing from corticosteroid treatment may find that the affected ear declines with age at a slightly faster rate than the unaffected side. An inner that has been damaged by any mechanism can eventually develop further degeneration and instability. This can manifest as fluctuating and progressive SNHL and/or episodic vertigo (Meniere’s syndrome) in about 3-5 percent of SSNHL patients. There are no reports suggesting risk of SSNHL in the second ear to be any greater than the risk to the first ear in an unaffected individual (1:5000 population/yr).
Patients who fail to recover symmetric hearing lose their ability to localize where sounds are coming from. This loss of sound localization is permanent. Also, those with persistent hearing asymmetry are at a disadvantage in adverse listening situations, such as high ambient noise, multiple talkers, foreign accent speakers, or rooms with poor acoustics. Hearing aids are of very limited use in rehabilitation of one-sided deafness if the opposite ear is normal. If the opposite ear is not normal, hearing aids on one or both ears may be beneficial.
Nearly all patients with SSNHL experience intense ear fullness or pressure and loud tinnitus with onset of their hearing loss. If they have partial hearing in the affected ear, sounds may seem harsh and distorted – like from a “blown” loudspeaker. These symptoms tend to abate gradually regardless of hearing outcome. By 6-12 months after SSNHL onset most patients find the tinnitus and fullness to be at a tolerable and less intrusive level most of the time.
Summary and Recommendations
Idiopathic SSNHL is a true otologic emergency. In patients with unilateral sudden hearing loss, there is a short window of opportunity of perhaps two-four weeks to initiate appropriate therapy. If treatment is delayed, prognosis is much worse and in most cases the hearing loss is irreversible. When a patient presents with unilateral ear blockage they must be evaluated for possible SSNHL.
The critical first step is to determine if there is really a hearing loss. This can be accomplished even over the telephone by simply asking the patient to move the phone from ear to ear or by making a soft sound, such as crinkling hairs, on each side for a comparison. If there is reduced hearing on the symptomatic side, the second step is to determine if it is conductive or sensorineural hearing loss. The definitive test is an audiogram. An effective (but not infallible) screening test is to have the patient hum aloud and note where they hear the sound, in the “good ear” or the “bad (i.e. blocked) ear.” The sound will localize toward a conductive loss and away from a sensorineural loss, so remember that “hearing the hum in the bad ear is good and hearing it in the good ear is bad.”
At this point in the assessment an actual careful history and physical examination of the ears and a focused neurological and balance examination is mandatory. If there is any suspicion of hearing loss or hearing asymmetry, then a complete audiogram is also indicated. If they audiogram confirms a unilateral SNHL, then MRI imaging with gadolinium is needed to rule-out neurological problems, such as demyelinating disease, tumor, or stroke. As soon as SSNHL has been identified, treatment should be started. Treatment should not be delayed while awaiting imaging studies, which can take days or weeks to schedule. Current standard treatment consists of a two-week burst and taper of oral prednisone, starting at 60 mg/day, or equivalent doses of methylprednisolone. Intratympanic steroid injections are equally, but not more, effective than oral treatment. There is some early evidence suggesting a benefit of combined oral and injection treatment, but it is too soon to know for certain if this is really more effective than single modality treatment.
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