Sudden hearing loss is an often underrecognized medical emergency that, without prompt treatment, can leave patients with permanent hearing deficits. This article provides clinicians in the primary care setting with the requisite information to recognize patients presenting with sudden hearing loss. Hearing loss can have a dramatic impact on a patient's quality of life and can lead to social isolation when it interferes with the ability to communicate.
Anatomy & Physiology of Hearing
To fully understand the nature of sudden hearing loss, it is important to have a basic understanding of how the human ear and auditory pathways work. The human ear is composed of the external, middle and inner ear structures. The external ear consists of the pinna and the external auditory canal (EAC), which funnel and direct sound toward the middle ear.1 The middle ear is an air-filled structure that is separated from the EAC by the tympanic membrane (TM) and houses the ossicular chain. The ossicular chain is composed of three bones: the malleus, incus and stapes. Sound waves are transmitted down the EAC to the TM. The resulting vibration of the TM cascades through the ossicles and subsequently stimulates the inner ear hearing mechanism.1 The auditory portion of the inner ear is the cochlea, which contains specialized sensory receptors known as hair cells. The hair cells convert mechanical energy into neural information, which is transmitted to the brain via afferent auditory nerve fibers.1
Hearing loss can be classified as conductive hearing loss (CHL), sensorineural hearing loss (SNHL) or mixed hearing loss. Mixed hearing loss has features of both CHL and SNHL. Conductive hearing loss can be caused by any condition that interferes with proper transmission of sound. The differential diagnosis of CHL includes cerumen impaction, foreign body in the external auditory canal, tympanic membrane perforation and middle ear effusion, among others. SNHL can be caused by pathologies of the cochlea or auditory nerve and includes entities such as age-related hearing loss, noise-induced hearing loss and sudden sensorineural hearing loss (SSNHL).
This article focuses on the evaluation and management of idiopathic sudden sensorineural hearing loss. At this time no consensus on the definition of SSNHL exists. The National Institute on Deafness and Other Communication Disorders defines SSNHL as a sensorineural hearing loss that occurs rapidly (over 72 hours) in one or both ears, in a 30-decibel or greater hearing loss occurs in at least three consecutive frequencies. Figure 1 (below) depicts a standard audiogram showing a unilateral SNHL.
Incidence & Etiology
The estimated incidence of SSNHL is 5 to 20 per 100,000 people per year; approximately 4,000 new cases are diagnosed annually in the United States.2.3 These figures may be an underestimate, since spontaneous recovery of hearing may dissuade some patients from seeking medical evaluation.3 SSNHL is most common between 43 and 53 years of age, with equal distribution between genders.4
The most common etiology of SSNHL is idiopathic, however, multiple underlying disorders can lead to SSNHL and must be considered in the differential diagnosis. Initial management and treatment differ depending on the suspected underlying cause. Retrocochlear (from cranial nerve VIII to the brain) pathologies such as stroke, vestibular schwannoma and demyelinating disorders account for approximately 1% of SSNHL cases.4 Other causes of SSNHL include, but are not limited to, Meniere disease, autoimmune disorders, trauma, syphilis, Lyme disease and perilymphatic fistula.4
The cause of ISNHL has not been defined. Up to 90% of SSNHL is idiopathic at presentation and a cause may only be identified in one-third of cases after long-term follow-up.5 Proposed theories for the development of ISSNHL include viral, vascular or multifactorial etiologies.5 Perhaps the most widely accepted theory is that of a viral cause. This notion is supported by the observation that many patients have experienced an antecedent upper respiratory tract infection prior to the onset of sudden hearing loss. However, the incidence of preceding URI symptoms in patients with SSNHL may be comparable to that of the general population.6
History and Physical Examination
The primary complaint of patients with SSNHL is the sudden onset of decreased or complete loss of hearing in one or both ears. Unilateral sudden hearing loss is far more common than bilateral loss. Additional presenting complaints accompanying the hearing loss may include aural fullness, pressure, tinnitus and vertigo. Patients should be questioned about recent otologic trauma, otorrhea and systemic neurologic symptoms. A detailed history is essential to identify possible underlying causes of sudden hearing loss.
An otoscopic examination of the external auditory canal, tympanic membrane and middle ear is often unremarkable in SNHL and frequently shows abnormal findings in CHL.5 Limited and conflicting evidence exists about the effectiveness of tuning fork tests in diagnosing hearing loss, and some authors have advocated against their use for general screening.7 However, no scientific studies have specifically evaluated the efficacy of tuning fork tests in the setting of sudden hearing loss. A recently published clinical practice guideline determined that tuning fork testing should be used to confirm audiometric findings and can assist in obtaining a preliminary diagnosis when audiometry is unavailable and results are unequivocal.5
The Weber test (depicted in Figure 2 at right) is performed by placing the tuning fork (usually 512 Hz) in the midline of the forehead or bridge of the nose. Sound will lateralize to the affected ear when a conductive hearing is present and away from the affected ear when a sensorineural hearing loss is present.
During the Rinne test (depicted in Figure 3 below left), the tuning fork is pressed over an area of the mastoid bone and then next to the opening of the external auditory canal on the ipsilateral side. A normal examination and a sensorineural hearing loss both result in louder air-conducted stimuli compared to bone-conducted stimuli (Rinne positive), whereas a significant conductive hearing loss would yield the opposite results.
A formal audiogram that includes pure tone thresholds of bone- and air- conducted sound, analyzed in conjunction with word discrimination scores, is the only definitive way to establish a diagnosis of SSNHL. It is important to note, however, that lack of availability of such testing should not prevent initiation of treatment.
Laboratory, Imaging and Diagnostic Studies
Given the numerous diagnostic possibilities that can account for SSNHL, several serologic and imaging studies can be considered. Routine or "shotgun" laboratory testing should not be performed because it is not cost effective, can lead to false-positive or false-negative results, and may delay treatment.5,8 Guided laboratory tests may be indicated if the history and physical examination suggest a specific cause of SSNHL. The patient with SSNHL should be evaluated for retrocochlear pathology - specifically for a vestibular schwannoma (VS).
Magnetic resonance imaging (MRI) with gadolinium contrast of the internal auditory canal, cerebellopontine angle and brainstem reaches nearly 100% specificity and sensitivity; thus it is the preferred diagnostic method when not contraindicated.8 The reported incidence of VS found in this setting ranges from 2.7% to 10.2%.5
A dedicated computed tomography (CT) scan of the temporal bone with contrast may be used when MRI is contraindicated. CT of the head or brain is generally not ordered in the evaluation of suspected idiopathic SSNHL and may, in fact, be harmful due to unnecessary radiation exposure. Auditory evoked brainstem response testing (ABR) is another option to evaluate for retrocochlear pathology, but patients must be counseled about its limitations.
Several treatment modalities, including corticosteroids, vasodilators, antiviral agents and hyperbaric oxygen therapy, have been proposed for treatment of SSNHL. Although substantial evidence of effectiveness for the use of systemic corticosteroids is lacking, it is the most widely used treatment modality in idiopathic SSNHL.
One randomized placebo-controlled trial showed a significant improvement in hearing recovery for the cohort of patients who were treated with prednisone or methylprednisolone (61%) compared to the group that received placebo (32%).9 However, a meta-analysis that reviewed five studies concluded that no evidence demonstrated that corticosteroids were superior to placebo.10 Another meta-analysis of medical treatments did find a small, but not statistically significant, improvement with corticosteroids compared to placebo.11
Corticosteroids are thought to be most beneficial if started within the first 2 weeks of symptom presentation and yield little if any benefit after 4 weeks from the initial onset of hearing loss.4 Due to the narrow therapeutic window allotted to initiate therapy, it is important to assure that an appropriate dosage of medication be given and that treatment not be delayed. Prednisone should be prescribed at 1 mg/kg/day as a single dose (typical dosage 60 mg/day). Therapy is usually tapered over the course of 10 to 14 days. If other systemic glucocorticoids are used, the dosing equivalent should be prescribed.
A short course of systemic steroid therapy is generally well tolerated. Side effects can include increased appetite, weight gain, difficulty sleeping and gastritis. More serious side effects include hyperglycemia, hypertension and cataract formation.
Corticosteroids can also be delivered through an intratympanic (IT) route. After proper anesthetic applied to the tympanic membrane, a small-gauge needle can be inserted directly through the ear drum to fill the middle ear space with a high concentration of steroid (e.g., dexamethasone 16 mg/mL). Some practices advocate tympanostomy tube insertion if repeated injections are planned. The optimal therapeutic time course has not been systematically studied, however most providers administer repeated IT injections over the course of several weeks. The procedure is done in the office and is well tolerated by most patients. Injection site pain, transient vertigo and tympanic membrane perforations can occur, albeit infrequently.
Traditionally, IT steroid therapy was used as salvage therapy for patients who had not responded to oral systemic therapy. This modality has become increasingly popular as first-line therapy in some practices, and it provides an alternative to oral therapy for patients with contraindications, such as poorly controlled diabetes mellitus, severe hypertension or peptic ulcer disease. A prospective, randomized, noninferiority trial involving 250 patients concluded that intratympanic treatment was not inferior to oral prednisone.11
Hyperbaric oxygen has been advocated as adjuvant therapy in the treatment of SSNHL. Evidence suggests possible benefit when used within 3 months of onset of hearing loss, and it may be most beneficial for patients with profound loss.4 Hyperbaric oxygen is not approved by the FDA for the treatment of SSNHL and the associated cost can be prohibitive.
Routine use of antiviral agents, thrombolytics, vasodilators, vasoactive substances and antioxidants are not indicated for SSNHL because the potential risks outweigh the benefits.4 A meta-analysis of randomized controlled trials concluded that the addition of antiviral medication for the treatment of SSNHL had no impact on recovery time or improvement of hearing.6
Prognosis & Follow-Up
Spontaneous recovery of hearing can be expected to occur in 45% to 65% of SSNHL patients without therapy; it most often occurs within the first 2 weeks after onset.3,8 Negative prognostic indicators include advanced patient age, prolonged duration of hearing loss prior to initiation of treatment, audiometric configuration and presence of vertigo. Patients in the negative prognostic categories of baseline profound deafness and dizziness have better results with oral steroid therapy compared to intratympanic steroid therapy alone.11
Patients should be counseled early on about options for aural rehabilitation, to proactively alleviate anxiety and fears about permanent hearing loss. Not all patients experience hearing recovery significant enough to receive benefit from wearing traditional hearing aids. A description of possible aural rehabilitation devices is beyond the scope of this article, but options do exist to improve the lives of patients who have not responded to therapy for SSNHL.
Quick Evaluation Needed
Any patient complaining of sudden hearing loss requires an expeditious evaluation, since prompt medical management can have a significant impact on hearing outcome. Hearing loss has a dramatic impact on quality of life and can have significant detrimental social consequences. Therefore, all patients should be offered proper counseling on both the natural course of SSNHL and the treatment options available.
If a sudden sensorineural hearing loss is suspected after a thorough history and physical examination, referral to an otolaryngologist should be sought. If the patient cannot be seen in a timely fashion by a specialist, oral administration of corticosteroids at an adequate dose should be offered unless contraindicated. Intratympanic steroid administration offers an acceptable alternative route of administration.
Evaluation for retrocochlear pathology (usually with MRI) is recommended in all patients with SSNHL. Routine laboratory and computed tomography imaging should not be obtained unless history or physical examination warrants special consideration. Patients who do not have full hearing recovery should be counseled by experienced clinicians about the options available for aural rehabilitation.
Ryan Marovich is a physician assistant in the Department of Otolaryngology at the University of Pittsburgh Medical Center (UPMC). Andrew McCall is an assistant professor in the Department or Otolaryngology at UPMC. Jason Fowler is a physician assistant in an ear, nose and throat practice in Meadville, Pa. The authors have completed disclosure statement and report no relationships related to this article.
1. Oghalai JS, Brownell WE. Anatomy & Physiology of the Ear. In: Lalwani AK, ed. Current Diagnosis and Treatment: Otolaryngology-Head and Neck Surgery. New York, NY: Lange Medical/McGraw Hill; 2008:577-595.
2. National Institute of Deafness and Communication Disorders. Sudden deafness. http://www.nidcd.nih.gov/health/hearing/Pages/sudden.aspx
3. Byl FM, Jr. Sudden hearing loss: eight years' experience and suggested prognostic table. Laryngoscope. 1984;94(5 Pt 1):647-661.
4. Rauch SD. Clinical practice: Idiopathic sudden sensorineural hearing loss. N Engl J Med. 2008;359(8):833-840.
5. Stachler RJ, Chandrasekhar SS. Clinical Practice Guideline: Sudden Hearing Loss. Otolaryngol Head Neck Surg. 2012;146(3 Suppl) S1-S35.
6. Shaikh JA, Roehm PC. Does Addition of Antiviral Medication to High-Dose Corticosteroid Therapy Improve Hearing Recovery Following Idiopathic Sudden Sensorineural Hearing Loss? Laryngoscope. 2011;121(11):2280-2281.
7. Bagai A, et al. Does this patient have hearing impairment? JAMA. 2006;295(4):416-428.
8. Kuhn M, et al. Sudden Sensorineural Hearing Loss: a review of diagnosis, treatment, and prognosis. Trends Amplif. 2011;15(3):91-105.
9. Wilson WR, et al. The efficacy of steroids in the treatment of idiopathic sudden hearing loss. A double blind clinical study. Arch Otolaryngol. 1980;106(12):772-776.
10. Labus J, et al. Meta-analysis for the effect of medical therapy vs. placebo on recovery of idiopathic sudden hearing loss. Laryngoscope. 2010;120(9):1863-1871.
11. Rauch SD, et al. Oral vs Intratympanic corticosteroid therapy for Idiopathic Sudden Sensorineural Hearing Loss. A randomized trial. JAMA. 2011;305(20):2071-2079.