Sudden Hearing Loss

Background

Definitions of sudden hearing loss have been based on severity, time course, audiometric criteria, and frequency spectrum of the loss. Abrupt as well as rapidly progressive losses have been included under a single definition of sudden hearing loss. Awakening with a hearing loss, hearing loss noted over a few days, selective low- or high-frequency loss, and distortions in speech perception have all been classified as sudden hearing losses. A commonly used criterion to qualify for this diagnosis is a sensorineural hearing loss of greater than 30 dB over 3 contiguous pure-tone frequencies occurring within 3 days' period. Fortunately, the vast majority of cases of sudden hearing loss are unilateral, and the prognosis for some recovery of hearing is good. Usually it presents as unilateral loss of hearing. An equal distribution of right- and left-sided cases should be expected; no greater risk for right-sided losses compared with left-sided losses seems to exist. Bilateral sudden hearing loss is rare, occurring in 1-2% of cases, and simultaneous bilateral involvement is very rare.

Sudden deafness or sudden sensorineural hearing loss (SNHL) has many possible etiologies.

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Pathophysiology

The postulated pathophysiology for idiopathic sudden sensory hearing loss (ISSHL) has 4 theoretical pathways, as follows:

• Labyrinthine viral infection
• Labyrinthine vascular compromise
• Intracochlear membrane ruptures
• Immune-mediated inner ear disease.

A disease process involving any of these theoretical possibilities could have sudden hearing loss as a symptom. Each theory may explain a fraction of the episodes of sudden sensory hearing loss, but none of the existing theories individually could account for all episodes.

Viral infection

The evidence to implicate viral infection as one cause of sudden idiopathic sensory hearing loss is circumstantial. Studies of patients with ISSHL show a moderate prevalence of recent viral-type illness. Sometimes, evidence of recent viral seroconversion or inner ear histopathology consistent with viral infection is present.

The weakest of these links is the history of a recent viral illness. Noncontrolled studies report that 17-33% of patients recall a recent viral illness. Should those numbers seem significant, 25% of patients without hearing loss visiting an otolaryngology clinic had experienced a viral-like illness within a month.

Comparing patients experiencing ISSHL with control patients has produced some evidence of viral seroconversion. Rates of seroconversion for the herpesvirus family were significantly higher in the population of patients with sudden hearing loss.

Finally, temporal bone histopathologic studies of patients who experienced ISSHL found damage in the cochlea consistent with viral injuries. Loss of hair cells and supporting cells, atrophy of the tectorial membrane, atrophy of the stria vascularis, and neuronal loss were observed. These patterns were similar to findings in documented cases of hearing loss secondary to mumps, measles, and maternal rubella. Viral infection can be implicated as a cause of ISSHL, but this cannot, as yet, be proven. Infections with mumps virus provide the best model for a virally induced sensorineural hearing loss. In one study of ISSHL, subclinical mumps infections were documented in 9 of 130 patients by positive immunoglobulin M (IgM) mumps antibodies.^[1]

Vascular compromise

The cochlea is an end organ with respect to its blood supply, with no collateral vasculature. Cochlear function is exquisitely sensitive to changes in blood supply. Vascular compromise of the cochlea due to thrombosis, embolus, reduced blood flow, or vasospasm seems to be a likely etiology for ISSHL. The time course correlates well with a vascular event, a sudden or abrupt loss. A reduction in oxygenation of the cochlea is the likely consequence of alterations in cochlear blood flow. Alterations in perilymph oxygen tension have been measured in response to changes in systemic blood pressure or intravascular carbon dioxide partial pressure (pCO₂).

Histologic evidence of cochlear damage following occlusion of the labyrinthine vessels was documented in temporal bone studies in animals and humans. Intracochlear hemorrhage was noted as an early development; subsequently, fibrosis and ossification of the cochlea evolved.

In one study, a partial overlap was found between classical coronary risk factors and risk factors for sudden hearing loss. Hypercholesterolemia and hypoalphalipoproteinemia (low HDL cholesterol levels) were not found to be apparent major risk factors for sudden hearing loss, whereas the GPIa C807T polymorphism, elevated fibrinogen levels, and smoking were associated with an increased risk for ISSHL.

In contrast to the above study, a historical prospective cohort study by Chang et al indicated that hypercholesterolemia is associated with an increased risk for idiopathic sudden sensorineural hearing loss (ISSNHL). Comparing nearly 74,000 patients with hypercholesterolemia with the same number of age-matched controls, the investigators found the incidence of ISSNHL to be 1.62 times greater in the hypercholesterolemia group.^[2]

Altogether, the various study findings suggest a vascular involvement in the pathogenesis of ISSHL. This may have important implications for the development of therapeutic and preventive strategies for ISSHL.^[3]

Intracochlear membrane rupture

Thin membranes separate the inner ear from the middle ear, and within the cochlea, delicate membranes separate the perilymphatic and endolymphatic spaces. Rupture of either or both sets of membranes theoretically could produce a sensory hearing loss. A leak of perilymph fluid into the middle ear via the round window or oval window has been postulated to produce hearing loss by creating a state of relative endolymphatic hydrops or by producing intracochlear membrane breaks. Rupture of intracochlear membranes would allow mixing of perilymph and endolymph, effectively altering the endocochlear potential. The theory of intracochlear membrane rupture was favored by Simmons and Goodhill, and histologic evidence has been documented by Gussen.^{[4, 5, 6]}

Immune-mediated inner ear disease

Sensorineural hearing loss induced by an immune process has gained greater and greater notoriety since the concept was introduced in 1979. Progressive sensorineural loss is observed with this condition. Whether or not sudden hearing loss occurs with immune-mediated inner ear disease is unclear, but immunologic activity in the cochlea is supported by greater and greater evidence. The association of hearing loss in Cogan syndrome, systemic lupus erythematosus, and other autoimmune rheumatologic disorders has been well documented. With better markers for inner ear autoimmunity, perhaps a greater linkage with ISSNHL will be found. A recent prospective study on 51 patients with ISSNHL supported the existence of multiple immune-mediated disorders in these patients.^[7]

Iron-deficiency anemia

A study by Chung et al indicated that iron-deficiency anemia increases the risk for sudden sensorineural hearing loss. The report, which involved about 4000 persons with sudden sensorineural hearing loss and approximately 12,000 controls, found that 4.3% of the group with hearing loss had previously been diagnosed with iron-deficiency anemia, compared with 3.0% of the control group. The link between hearing loss and anemia seemed to be strongest in persons aged 44 years or younger.^[8]

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Epidemiology

Frequency

United States

Estimates of the annual incidence of sudden sensory hearing loss range from 5-20 cases per 100,000 persons. Many cases likely go unreported, and the incidence may be higher. A sudden hearing loss may resolve before the patient can be evaluated medically, making it unlikely for that individual to seek care.

International

A South Korean study, by Kim et al, found the mean annual incidence of unilateral sudden sensorineural hearing loss (SSNHL) to be 17.76 cases per 100,000 population, with a rise in the unilateral condition’s monthly incidence occurring over the report’s 5-year study period.^[9]

Sex

The female-to-male distribution appears to be equal. Combined data from several studies show a slight male preponderance, at 53%. Sex does not seem to be a risk factor. However, a large study of 1220 patients had slightly more females.^[10]  Moreover, the aforementioned South Korean study by Kim et al reported a slightly greater incidence of unilateral SSNHL in women, with the male-to-female ratio being 1:1.35.^[9]

Age

People of all age groups are affected by sudden hearing loss, but fewer cases are reported in children and the elderly. The peak incidence appears to be in the sixth decade of life. Young adults have incidence rates similar to those of middle-aged adults. The median age at presentation ranges from 40-54 years. (In the Kim study from South Korea, however, most patients presenting with unilateral SSNHL were in their 60s.^[9] ) The occurrence of sudden hearing loss across all age groups is an indication of the multifactorial nature of this clinical problem.

A literature review by Sara et al indicated that the onset of bilateral sudden sensorineural hearing loss tends to occur at a younger age than the unilateral form.^[11]

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History

Sudden SNHL has been called an otologic emergency. Patient evaluation should proceed promptly and expeditiously. Early presentation to a physician and early institution of treatment improves the prognosis for hearing recovery. The immediate goal is discovering a treatable or defined cause of the sudden hearing loss. 

• Information about the onset, time course, associated symptoms, and recent activities may be helpful.
• Past medical history may reveal risk factors for hearing loss.

  • All medications, including over-the-counter products, must be described.
  • Aspirin can cause a reversible sensorineural hearing loss, and the list of aspirin-containing products is extensive.

   

  

   

A study by Hung et al indicated that a previous diagnosis of chronic rhinosinusitis is significantly associated with the development of sudden SNHL (adjusted odds ratio for having prior chronic rhinosinusitis = 1.36 in patients with sudden SNHL), particularly in patients aged 44 years or less. For patients over age 60 years, however, the association seemed no longer to exist.^[12]

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Physical

Perform a careful head and neck examination, with special attention to the otologic and neurologic examination.

Tuning fork tests and a fistula test using pneumatic speculum must be performed.

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Causes

The term sudden hearing loss encompasses defined causes and ISSHL. In the evaluation of a sudden sensorineural hearing loss, a definite etiology may be uncovered. The following have been associated with sudden hearing loss:

• Infection - Bacterial (eg, meningitis, syphilis), viral (eg, mumps, cytomegalovirus, varicella/zoster)
• Inflammation – Sarcoidosis, Wegener granulomatosis, Cogan syndrome
• Vascular - Hypercoagulable states (eg, Waldenstrom macroglobulinemia), emboli (eg, postcoronary artery bypass graft [CABG] surgery), postradiation therapy
• Tumor -Vestibular schwannoma, temporal bone metastases, carcinomatous meningitis
• Trauma -Temporal bone fracture, acoustic trauma, penetrating temporal bone injuries
• Toxins - Aminoglycoside antimicrobials, cisplatin

The greater number of cases, however, fit into the idiopathic category. ISSHL is the frustrating endpoint for most patients with sudden hearing loss. However, a study by Passamonti et al indicated that the risk for ISSHL is increased in patients with hyperhomocysteinemia and high levels of factor VIII. The study, which included 118 patients with a first occurrence of ISSHL and 415 healthy controls, found that deficiencies of antithrombin or protein C or S, as well as the presence of cardiovascular risk factors (ie, arterial hypertension, hyperlipidemia, diabetes, smoking), may also increase the risk for ISSHL.^[13]

Despite the detailed history taking, physical examination, and laboratory investigations, ascertaining the pathophysiology of the events in sudden hearing loss may not be possible; therefore, the cause and treatment of these cases may be more presumptive than factual.

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Laboratory Studies

Routine, non-targeted, laboratory testing is not recommended.^[14] Laboratory studies should be directed by the history and physical examination findings.

• Fluorescent treponemal antibody-absorption (FTA-Abs) for syphilis
• Antinuclear antibodies (ANA), rheumatoid factor, and erythrocyte sedimentation rate (ESR) for autoimmune diseases
• International normalized radio (INR), activated partial thromboplastin time (aPTT), and clotting time for coagulopathy
• CBC count and differential for infection
• Thyroid-stimulating hormone (TSH) for thyroid disease
• Fasting blood glucose for diabetes mellitus
• Cholesterol and triglycerides for hyperlipidemia

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Imaging Studies

Approximately 1-2% of patients with ISSHL have internal auditory canal (IAC) or CPA tumors. Conversely, 3-12% of patients with vestibular schwannomas present with sudden hearing loss.

Magnetic resonance imaging (MRI) with gadolinium diethylenetriamine-pentaacetic acid (DPTA) enhancement is the criterion standard test for diagnosing CPA masses, especially because a 30-40% false-negative rate exists with auditory brainstem response (if hearing levels permit). The cost issue for MRI has been addressed by performing limited studies using fast spin echo techniques.

According to 2012 guidelines from the American Academy of Otolaryngology-Head and Neck Surgery Foundation (AAO-HNSF), computed tomography (CT) scans are not helpful and expose the patient to ionizing radiation. Therefore, CT scans are not recommended in the initial evaluation of patients with presumptive SSNHL.^[14] However, in young patients, for whom only a small possibility of detecting a vestibular schwannoma exists, a noncontrast temporal bone CT scan could be obtained. Anatomic defects such as a Mondini dysplasia or enlarged vestibular aqueduct might account for a sudden hearing loss.

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Other Tests

See the list below:

• Audiometry, including pure-tone and speech tests and immittance (tympanometry and acoustic reflex) tests, is mandatory. Testing can be directed by information gleaned from the history and physical examination. Obtaining those laboratory tests for which the results may influence the treatment plan is wise.
• Auditory brainstem response testing and otoacoustic emissions (OAE) tests may provide additional information regarding the functional integrity of the auditory system.

  • OAE testing can provide information about cochlear function, and the auditory brainstem response can be used to assess auditory nerve function.
  • The auditory brainstem response and OAE results may also assist in diagnosing a functional hearing loss.

   

  

   
• Vestibular tests are not mandatory and are obtained when indicated by the history and physical examination findings.

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Medical Care

No preferred treatment regimen exists for sudden hearing loss.

Treatment can be based upon a rational approach. Based on the history, physical examination findings, and laboratory results, if no definitive or treatable etiology is found, the treatment regimen should be dictated by the most likely factors involved. Remembering that all the medications used in treatment of sudden sensory hearing loss have potential adverse effects, the best course of action must be agreed upon by the physician and the patient.

The treatment regimens for ISSHL are varied, and this diversity reflects both the different etiologies that may cause sudden hearing loss and the uncertainty in diagnosis. The therapies can be grouped by mechanism of action. Experimental outcomes for some of these therapies are discussed under Prognosis.

Vasodilators

Theoretically, vasodilators improve the blood supply to the cochlea, reversing hypoxia. In general, these are agents with effects on the systemic vasculature. Papaverine, histamine, nicotinic acid, procaine, niacin, and carbogen (5% carbon dioxide) have been used in attempts to improve cochlear blood flow. Carbogen inhalation has been shown to increase perilymph oxygen tension. Carbogen has also increased measured transcutaneous and subcutaneous oxygen tension without significantly affecting carbon dioxide tension. A study found that the efficiency of carbogen combined with drugs is superior to drug therapeutics in the treatment of sudden deafness.^[15]

Rheologic agents

By altering blood viscosity with the use of low molecular weight dextrans, pentoxifylline, or anticoagulants (eg, heparin, warfarin), better oxygen delivery might be achieved. Dextrans cause a hypervolemic hemodilution and affect factor VIII, with both these effects influencing blood flow. Pentoxifylline affects platelet deformability, presumably improving blood flow. Anticoagulants interfere with the coagulation cascade as a mechanism to avoid formation of thrombi and emboli.

Anti-inflammatory agents

Corticosteroids are the primary anti-inflammatory agents used to treat ISSHL. The mechanism of action in sudden hearing loss is unknown, although reduction of cochlear and auditory nerve inflammation is the presumed pathway. However, the value of steroids in the treatment of idiopathic sudden sensorineural hearing loss (ISSNHL) remains unclear.^{[16, 17, 18, 19, 20]}

In a randomized, controlled study, intratympanic injection of dexamethasone is shown to effectively improve hearing in patients with severe or profound SSNHL after treatment failure with standard therapy and is not associated with major side effects.^[21] Similar results were reported in yet another study.^[22] Its trial to salvage hearing in cases where other medical therapy fails is justified.

A prospective study by Battaglia et al indicated that a greater percentage of patients with ISSNHL recover following combination therapy with high-dose prednisone taper (HDPT) and intratympanic dexamethasone (IT-Dex) than do those treated with HDPT alone. The investigators found that among those individuals with class-D hearing, 49% of patients who underwent combination therapy (10 mg/mL of IT-Dex every week for 3 wks, administered concomitantly with 60 mg/day of HDPT for 7 days, with a 7-day taper) recovered a serviceable amount of hearing, compared with 29% of patients who received only HDPT. It was also found that the likelihood of hearing recovery was higher when combination therapy was administered within 7 days of the onset of ISSNHL, with 56% of class-D patients achieving serviceable hearing.^[23]

However, a prospective, randomized, multicenter clinical trial by Tsounis et al reported that in patients with ISSNHL, systemic, intratympanic, and combined systemic/intratympanic steroid administration led to similar hearing outcomes. By 90-day follow-up, mean hearing improvements of 29.0 dB HL, 27.0 dB HL, and 29.8 dB HL, respectively, had been achieved.^[24]

A paucity of data exists on the use of nonsteroidal anti-inflammatory agents.

Antiviral agents

Acyclovir and amantadine have had limited use in treating ISSHL, presuming a viral etiology. Two newer agents, famciclovir and valacyclovir, have not yet been reported upon as treatment for sudden hearing loss. They are structurally similar to acyclovir, affecting viral thymidine kinase. They inhibit viral DNA polymerase, preventing viral DNA replication.

Diuretics

Under the assumption that some episodes of ISSHL are secondary to cochlear endolymphatic hydrops, diuretic therapy has been used as treatment. As in Ménière disease, the mechanism of action for diuretics in sudden hearing loss is not understood.

Triiodobenzoic acid derivatives

These agents are thought to affect the stria vascularis and assist in maintaining the endocochlear potential. Diatrizoate meglumine, an angiographic contrast agent, was rather serendipitously found to have an effect on sudden hearing loss and is the most commonly used derivative of triiodobenzoic acid.

Hyperbaric oxygen

Presumably by increasing oxygen tension, hyperbaric oxygen has been evaluated as therapy for sudden hearing loss. The reported series are small, but the topic has been reviewed by Lamm et al in 1998.^[25]

A study by Narozny (2004) concluded that hyperbaric oxygen therapy (consisting of exposure to 100% oxygen at a pressure of 250 kPa for a total of 60 minutes) in a multi-place hyperbaric chamber with high doses of glucocorticoids improves the results of conventional sudden sensorineural hearing loss treatment; the best results are achieved if the treatment is started as early as possible.^[26]

Some other authors also believe that for people with early presentation of idiopathic sudden sensorineural hearing loss, the application of hyperbaric oxygen therapy can significantly improve hearing loss. However, a beneficial effect of hyperbaric oxygen therapy on chronic presentation of idiopathic sensorineural hearing loss and/or tinnitus is not evident.^[27]

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Surgical Care

Repair of oval and round window perilymph fistulae (PLF) has been used in cases of ISSHL associated with a positive fistula test result or a history of recent trauma or barotrauma.

• Perilymph leaks could produce sudden hearing loss in accordance with the intracochlear membrane rupture theory. Alternatively, low perilymph pressure could produce a relative state of cochlear endolymphatic hydrops.
• Controversy exists regarding the role of surgical repair of perilymphatic fistulae because no universal standard exists for positive identification of a fistula. The tau transferrin test on perilymph fluid has not proven to be useful in the diagnosis of this entity.

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Guidelines Summary

AAO-HNSF guidelines

The American Academy of Otolaryngology–Head and Neck Surgery Foundation (AAO-HNSF) issued clinical practice guidelines for sudden hearing loss on August 1, 2019.^[28]

Presentation

Sensorineural hearing loss (SNHL) should be differentiated from conductive hearing loss (CHL) in patients who present with sudden hearing loss (SHL).

Patients with suspected sudden sensorineural hearing loss (SSNHL) should undergo history and physical examination for bilateral SHL, recurrent SHL, and/or focal neurologic findings.

Workup

Patients with presumptive SSNHL should not undergo routine head CT scanning during the initial evaluation.

Audiometry should be performed as soon as possible to confirm a diagnosis of SSNHL, within 14 days of symptom onset.

Routine laboratory tests should not be performed in the workup of SSNHL.

Patients with SSNHL should undergo MRI or auditory brainstem response (ABR) to evaluate for retrocochlear pathology.

Patient education

Patients with SSNHL should be educated regarding the condition’s natural history and the potential benefits and risks of treatment.

Treatment

Corticosteroids may be offered to patients with SSNHL as initial therapy within 2 weeks of onset.

Hyperbaric oxygen therapy (HBOT), in combination with steroid therapy, may be offered to patients with SSNHL within 2 weeks of onset.

HBOT, in combination with steroid therapy, may be offered as salvage therapy to patients with SSNHL within 1 month of onset.

Patients with an incomplete recovery from SSNHL should be offered intratympanic steroid therapy 2-6 weeks after symptom onset.

Antiviral therapy, thrombolytic therapy, vasodilator therapy, and vasoactive substances should not be routinely prescribed to patients with SSNHL.

Outcome assessment

At the conclusion of treatment and then 6 months thereafter, follow-up audiometric evaluation should be performed in patients with SSNHL.

Rehabilitation

Patients with SSNHL who have residual hearing loss and/or tinnitus should be educated about the potential benefits of audiologic rehabilitation and other supportive measures.

ACMG guidelines

The 2014 American College of Medical Genetics and Genomics (ACMG) guidelines for clinical evaluation and etiologic diagnosis of hearing loss are summarized below. Medical histories may be helpful in differentiating between acquired versus inherited causes of hearing loss. According to the ACMG, histories aimed at assessing hearing loss should include the following^[29] :

• Prenatal history of maternal infections (eg, cytomegalovirus, rubella, syphilis) or drug exposures (eg, thalidomide, retinoic acid)
• Neonatal history, including premature birth, low birth weight, birth hypoxia, hyperbilirubinemia, sepsis, and exposure to ototoxic medications
• Postnatal history, including viral illnesses, bacterial meningitis, head trauma, noise exposure, and exposure to ototoxic medications
• Audiometric assessment of the hearing loss; age of onset; progressive, nonprogressive, or fluctuating nature of the hearing loss; laterality, symmetry, severity, and configuration of the hearing loss; and the presence or absence of vestibular dysfunction or auditory neuropathy

The family medical history should concentrate on the following^[29] :

• First- and second-degree relatives with hearing loss or with features commonly associated with hearing loss (such as pigmentary, branchial, or renal anomalies) or sudden cardiac death
• A pattern of inheritance
• Ethnicity and country of origin
• A common origin from ethnically or geographically isolated areas
• Consanguinity

The physical examination should focus on the following^[29] :

• Unusual facial appearance, with attention to asymmetry
• Pigmentary anomalies
• Neck, skin, facial, or ear anomalies
• Neurologic abnormalities
• Balance disturbances
• Skeletal abnormalities
• Other unusual physical findings

For individuals with physical findings and histories that do not suggest a known syndrome or environmental cause of hearing loss, a tiered diagnostic approach is needed that includes the following^[29] :

• Genetic counseling and, after informed consent, genetic testing
• Single-gene testing in cases in which a specific etiology is suspected from the history and physical findings
• In the absence of any specific clinical indications and for apparent autosomal recessive inheritance, testing for DFNB1-related hearing loss (due to mutations in GJB2 and adjacent deletions in GJB6)
• If initial genetic testing is negative, consider genetic testing using gene panel tests and next-generation sequencing (NGS) technologies; however, the clinician must be aware of the genes included in the test (panel) and the performance characteristics of the platform chosen, including coverage, analytic sensitivity, and what types of mutations will be detected
• Test results should be communicated through genetic counseling regardless of whether they are positive, negative, or inconclusive
• If genetic testing reveals mutation(s) in a hearing loss–related gene, mutation-specific genetic counseling should be provided, followed by medical evaluations and referral to a multidisciplinary care center, when available
• Consider temporal bone imaging by CT scanning or MRI, particularly if the diagnosis remains unclear, if cochlear implantation is being considered, if auditory neuropathy is noted, in cases of progressive hearing loss, or if other clinical concerns exist
• If genetic testing fails to identify an etiology for a patient's hearing loss, the possibility of a genetic or acquired etiology remains and further genetic testing may be pursued in a research setting; periodic follow-up care every 3 years with a geneticist may be appropriate to identify syndromic forms of hearing loss that may appear as individuals age and to discuss new genetic tests that may have become available

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Medication Summary

No high-quality, randomized, controlled trial exists demonstrating the efficacy of any medical therapy in ISSHL. Hence, no single treatment has been unequivocally shown to be effective, but many strategies have been proposed. Carbogen (5% CO₂ +95% oxygen) inhaled for 30 min, 6 times per day (q2h during the day) for 5 days has been used.^[30]

A prospective, randomized, noninferiority trial compared the effectiveness of oral prednisone with the effectiveness of intratympanic methylprednisolone in 250 participants with idiopathic sudden sensorineural hearing loss. After 6-month follow-up, the results indicated that based on hearing level 2 months after treatment, the treatments showed similar overall efficacy.^[31]

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Prednisone (Orasone, Meticorten, Deltasone, Wysolone)

• Dosing, Interactions, etc.

Clinical Context:  May decrease inflammation by reversing increased capillary permeability and suppressing PMN activity.

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Dexamethasone (Decadron)

• Dosing, Interactions, etc.

Clinical Context:  Intratympanic dexamethasone increases cochlear blood flow after ischemia-induced injury.

Has many pharmacologic benefits but significant adverse effects. Stabilizes cell and lysosomal membranes, increases surfactant synthesis, inhibits prostaglandin and proinflammatory cytokines (eg, TNF-alpha, IL-6, IL-2, and IFN-gamma). The inhibition of chemotactic factors and factors that increase capillary permeability inhibits recruitment of inflammatory cells into affected areas. Suppresses lymphocyte proliferation through direct cytolysis and inhibits mitosis. Breaks down granulocyte aggregates, and improves pulmonary microcirculation. Adverse effects are hyperglycemia, hypertension, weight loss, GI bleeding or perforation synthesis, cerebral palsy, adrenal suppression, and death. Most of the adverse effects of corticosteroids are dose-dependent or duration-dependent.

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Class Summary

These agents have anti-inflammatory properties and cause profound and varied metabolic effects. Corticosteroids modify the body's immune response to diverse stimuli.

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Hydrochlorothiazide/triamterene (Dyazide, Maxzide)

• Dosing, Interactions, etc.

Clinical Context:  Inhibits reabsorption of sodium in distal tubules, causing increased excretion of sodium and water as well as potassium and hydrogen ions.

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Class Summary

These agents are beneficial in the treatment of fluid retention.

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Hyaluronidase (Hylase, Wydase Injection)

• Dosing, Interactions, etc.

Clinical Context:  Stimulates hydrolysis of hyaluronic acid, one of the chief ingredients of tissue cement, which offers resistance to diffusion of liquids through tissues. Used to aid in absorption and dispersion of injected drugs

Intratympanic hyaluronic acid may increase permeability of membranes and influences distribution of dexamethasone within inner ear.

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Class Summary

Agents in this category may help in the dispersion and absorption of drugs.

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Further Outpatient Care

Patients who continue to have a significant hearing loss require aural rehabilitation.

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Prognosis

Fortunately, the spontaneous recovery rates for sudden SNHL are generally good. These rates range from 47-63%, with the caveat that different studies used different criteria for degrees of recovery. Ideally, criteria will be established by which to measure hearing improvement.

Negative prognostic factors include the following:

• Age younger than 15 years or older than 65 years
• Elevated ESR (>25)
• Vertigo or vestibular changes evident on ENG
• Hearing loss in the opposite ear
• Severe hearing loss

Prognostic factors affecting outcome in patients with sudden SNHL have been postulated. Vertigo or imbalance seems to portend a lower recovery rate. Two studies, in addition, found severe vertigo associated with more cases of high-frequency or profound hearing loss. This association could be explained anatomically by the close proximity of the basal turn of the cochlea to the vestibule.

A study by Passamonti et al indicated that the presence of hyperhomocysteinemia or cardiovascular risk factors (ie, arterial hypertension, hyperlipidemia, diabetes, smoking) signals worse clinical outcomes in ISSHL.^[13]

A study by Lin et al found evidence that in patients with ISSHL, higher ratios of low-density lipoprotein cholesterol (LDL-C) to high-density lipoprotein cholesterol (HDL-C) indicate a poorer prognosis for hearing recovery. According to the study, which involved 166 patients with ISSHL, patients who made a complete recovery had a significantly lower LDL-C/HDL-C ratio than did those who made only minimal recovery.^[32]

A literature review by Sara et al indicated that bilateral sudden SNHL has a worse recovery rate than does unilateral hearing loss.^[11]

A study by Lee et al indicated that in cases of sudden SNHL caused by intralabyrinthine hemorrhage (ILH), the prognosis is worse than in ISSNHL, ie, non-ILH cases. Patients whose condition arose from ILH had a worse final recovery threshold than did the other patients, and they apparently achieved hearing recovery at high frequencies (2000, 4000, 8000 Hz) less often than at low frequencies (250, 500, 1000 Hz). Moreover, 92% of the ILH patients complained of dizziness. The study included 35 patients, including 12 with ILH.^[33]

Considerable controversy exists regarding the prognosis in sudden hearing loss. Existing studies have not provided answers to questions regarding spontaneous recovery rate, the best therapeutic regimen, prognostic factors in recovery, and the pathophysiology of sudden hearing loss. These are questions that require a randomized controlled clinical trial of adequate size. Given the apparent rate of spontaneous recovery, the prognosis for some hearing recovery for patients with sudden SNHL is moderate. Selection bias is likely to affect most studies of ISSHL because patients with sudden hearing loss and spontaneous recovery within a few days probably do not seek medical evaluation. The true spontaneous recovery rate is unknown.

A retrospective study by Kang et al indicated that prognostic factors for recovery from ISSNHL include patient age, the extent of the initial hearing loss, the initial speech discrimination score, the initial pure tone threshold, and the period of time between the start of symptoms and the beginning of treatment.^[34]

A review of outcomes for the various therapeutic regimens produces conflicting results, again because of differences in reporting. With different inclusion criteria, exclusion criteria, recovery criteria, and duration of follow-up, comparisons between studies are often not valid. Many studies lack control subjects.

Several studies using vasodilator therapy as a component of treatment did not show significant differences from placebo. However, in 1996, Fetterman et al reported their best recovery results (63% improved pure-tone average [PTA] by more than 10 dB or speech discrimination more than 15%) when treatment included vasodilators.^[35] Based on controlled studies, little data support vasodilator therapy.

Several studies assessing low molecular weight dextrans and/or pentoxifylline did not demonstrate recovery rates better than placebo. One exception by Redleaf et al in 1995 reported 64% of patients improving.^[36] In this study, concomitant diatrizoate therapy was also administered, and no placebo arm was used.

Corticosteroid therapy has been investigated with varying outcomes. Published recovery rates range from 41-61%. In 1980, Wilson et al demonstrated a significant improvement, finding 61% improved on oral corticosteroids compared to a 32% improvement rate on placebo.^[37] They also stratified their patient groups by audiometric patterns, and determined that hearing losses from 40-90 dB responded better to steroid therapy; 78% improved.

Diatrizoate has not been studied to any great extent. In 1987, Wilkins et al found no significant difference in recovery using diatrizoate in a multidrug regimen compared to spontaneous recovery rates.^[38] Redleaf et al reported a beneficial effect using diatrizoate and dextran, improving 64% of patients.^[36] Interestingly, using the hearing recovery criteria of Wilkins et al, recalculated data from the 1995 Redleaf study indicated only a 36% recovery rate to a classification of complete or good.

A review of hyperbaric oxygen therapy found a beneficial effect, especially if therapy was instituted within 2-6 weeks of the onset of the hearing loss. Fifty percent of patients improved by 20 decibels. If therapy was delayed, less improvement was found, with no beneficial effect for delays of longer than 3 months.

At an average 8-year follow-up, a study by Härkönen et al indicated that patients who suffered unilateral ISSNHL who had not recovered normal hearing in the affected ear experienced not just lower quality of hearing but also significantly lower quality of life, as well as more tinnitus and greater balance problems, than did patients with unilateral ISSNHL whose hearing did recover to normal.^[39]

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Patient Education

The American Academy of Otolaryngology-Head and Neck Surgery Foundation (AAO-HNSF) guidelines recommend physicians educate patients with sudden hearing loss about the natural history of the condition, the benefits and risks of medical interventions, and the limitations of existing evidence regarding efficacy. Physicians should obtain follow-up audiometry within six months of diagnosis and counsel patients with incomplete hearing recovery about the possible benefits of amplification and hearing assistive technology and other supportive measures.^[14]

For excellent patient education resources, visit eMedicineHealth's Ear, Nose, and Throat Center. Also, see eMedicineHealth's patient education article Hearing Loss.

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