Sudden Sensorineural Hearing Loss

TITLE: Sudden Sensorineural Hearing Loss
SOURCE: Grand Rounds Presentation, UTMB, Dept. of Otolaryngology
DATE: June 13, 2001
RESIDENT PHYSICIAN: Christopher Muller, MD
FACULTY PHYSICIAN: Jeffrey Vrabec, MD
SERIES EDITOR: Francis B. Quinn, Jr., MD

"This material was prepared by resident physicians in partial fulfillment of educational requirements established for the Postgraduate Training Program of the UTMB Department of Otolaryngology/Head and Neck Surgery and was not intended for clinical use in its present form. It was prepared for the purpose of stimulating group discussion in a conference setting. No warranties, either express or implied, are made with respect to its accuracy, completeness, or timeliness. The material does not necessarily reflect the current or past opinions of members of the UTMB faculty and should not be used for purposes of diagnosis or treatment without consulting appropriate literature sources and informed professional opinion."

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Introduction

Sudden hearing loss (SHL) is a medical emergency for which definitive diagnosis and treatment is still largely unknown. It was first described in the literature by De Klevn in 1944. SHL generally a refers to hearing loss of sensorineural origin. It has been defined for research purposes and has been accepted by most authorities as 30 dB or more sensorineural hearing loss over at least three contiguous audiometric frequencies occurring within 3 days or less.

Estimates report approximately 15,000 reported cases of SHL per year worldwide with 4000 of those occurring in the United States. One in every 10,000 to 15,000 people will suffer from this condition, with the highest incidence occurs between 50 and 60 years of age. The lowest incidence is between 20 and 30 years of age. Of the patient suffering from SHL, 2% are bilateral. In most series, the incidence was nearly equal in men and women.

There are many potential causes of SHL, but despite extensive evaluation, the majority of cases elude definitive diagnosis and therefore, remain idiopathic. Reports estimate that the etiology of SHL is diagnosed in only 10% of cases. Suggested causes of idiopathic sudden sensorineural hearing loss (ISSNHL) include viral infections, immunologic, vascular compromise, and intracochlear membrane breaks. It is unlikely that any single one of these pathophysiologic processes explains all cases of ISSNHL. Treatment regimens aimed at addressing the underlying problem in each of these states have been suggested including decreasing cochlear inflammation, improving inner ear blood flow and oxygenation, and reestablishing the endocochlear potential.

Etiology

The etiology of SHL can be broken down into broad categories: (1) viral and infectious, (2) autoimmune, (3) labyrinthine membrane rupture/traumatic, (4) vascular, (5) neurologic, and (6) Neoplastic. There are multiple conditions within each of these categories that have been associated with sudden hearing loss. The following is a partial list of reported causes of SHL:

Infectious Meningococcal meningitis
Herpesvirus (simplex, zoster, varicella, cytomegalovirus)
Mumps
Human immunodeficiency virus
Lassa fever
Mycoplasma
Cryptococcal meningitis
Toxoplasmosis
Syphilis
Rubeola
Rubella
Human spumaretrovirus
Autoimmune Autoimmune inner ear disease (AIED)
Ulcerative colitis
Relapsing polychondritis
Lupus erythematosus
Polyarteritis nodosa
Cogan’s syndrome
Wegener’s granulomatosis
Traumatic Perilymph fistula
Inner ear decompression sickness
Temporal bone fracture
Inner ear concussion
Otologic surgery (stapedectomy)
Surgical complication of nonotologic surgery
Vascular Vascular disease/alteration of microcirculation
Vascular disease associated with mitochondriopathy
Vertebrobasilar insufficiency
Red blood cell deformability
Sickle cell disease
Cardiopulmonary bypass
Neurologic Multiple sclerosis
Focal pontine ischemia
Migraine
Neoplastic Acoustic neuroma
Leukemia
Myeloma
Metastasis to internal auditory canal
Meningeal carcinomatosis
Contralateral deafness after acoustic neuroma surgery

History and Physical

Evaluation and management of SHL should be considered medically urgent, if not an emergency. The primary goal is to rule out any treatable causes.

Diagnostic evaluation of the patient with sudden hearing loss begins with a thorough history and physical exam. Details of the circumstances surrounding the hearing loss and the time course of its onset should be elicited. Associated symptoms, such as tinnitus, vertigo or dizziness, and aural fullness should also be asked about. Clinical experience has shown that about one-third of patients note their hearing loss upon first awakening in the morning, and that about one- half the cases will have associated vertigo. Patients should also be questioned about previous otologic surgery, ototoxic drug use, and previous or concurrent viral or upper respiratory tract infections. Any history of trauma, straining, diving, flying, and intense noise exposure should be noted. Past medical history of other diseases associated with sudden hearing loss should also be obtained such as diabetes, autoimmune disorders, malignancies, neurologic conditions (multiple sclerosis), and hypercoagulable states. African-Americans should be asked about sickle cell disease.

A complete head and neck exam should be performed on all patients with sudden hearing loss. More often than not, the exam will be unremarkable, however, any processes such as middle ear effusions, infections, cholesteatoma, and cerumen impaction should be excluded. A thorough neurological exam including Weber and Rinne, cerebellar and vestibular testing should be performed.

Diagnostic Testing

An audiogram (pure tone, speech, tympanometry, including stapedial reflex testing) should be performed on all patients with sudden hearing loss. The audiogram is the foundation of the diagnosis and provides prognostic information. Serial testing provides documentation of the progression or resolution of the hearing loss and response to treatment. In addition it may help exclude patients with secondary gain or with pseudohypacusis.

The following is a list of laboratory studies that can be ordered. Initial screening tests should be directed based on history and suspected conditions.

1) Complete blood count (CBC)

2) Erythrocyte sedimentation rate (ESR)

3) Glucose

4) Cholesterol/triglycerides

5) T3, T4, TSH

6) PT, PTT

7) VDRL, RTA-ABS (MHA-TP)

8) HIV

9) Lyme titer

Magnetic resonance imaging (MRI) is recommended by the majority of authors for patients with asymmetric hearing loss. In one survey of 79 otolaryngologists, 38% would order imaging on the patient’s initial visit. MRI is useful in evaluating for acoustic tumors, multiple sclerosis and cerebrovascular accidents. There are some proponents of following these patients and imaging only if asymmetric hearing persists. However, Berg et al., in a series of acoustic neuromas showed that 13% presented with sudden hearing loss, and of these 23% recovered auditory function.

Known Treatable Causes of Sudden Sensorineural Hearing Loss

Autoimmune

Autoimmune hearing loss may be associated with or part of systemic autoimmune diseases such as Cogan's syndrome, Wegener’s granulomatosis, polyarteritis nodosa, temporal arteritis, Buerger’s disease (thromboangitis obliterans), and systemic lupus erythomatosis, or may be primary to the inner ear. The pathogenesis of immune-mediated sensorineural deafness and vestibular dysfunction are unclear, but are presumed to include: vasculitis of vessels supplying the inner ear, autoantibodies directed against inner ear antigenic epitopes, or cross-reacting antibodies. Autoimmune hearing loss implies that inner ear proteins are recognized immunologically as foreign or non-self. Some authors contend that there is no such entity as autoimmune hearing loss as these putative inner ear antigens are as of yet unknown.

Cogan's syndrome (CS) is an autoimmune disease of the cornea and vestibuloauditory apparatus that was first described by Cogan, an ophthalmologist, in the 1940s. It occurs primarily in young adults (average age of onset 22-29 years) and typically presents with interstitial keratitis (IK) and Meniere's-like attacks of vertigo, ataxia, tinnitus, nausea, vomiting, and hearing loss which develop within several months of each other. CS may also be associated with other systemic manifestations of the inflammatory process such as Takayasu's-like or medium-sized vessel vasculitis. Approximately 10% of patients develop aortitis within weeks to years after the onset. Hearing fluctuation in CS coincides with disease exacerbations and remissions. Its course often culminates in deafness. One series reported that 12 out of 18 patients (67%) developed bilateral deafness.

The cause of CS is unknown. Microbial etiology has been suggested by some as URTI precede nearly 40% of patients who present with this disease. Clinical parallels between syphilis and CS have led some to belief that CS may be caused by Borrelia burgdorferi. However, evidence so far has been inconclusive. There have also been links to Chlamydia species with CS and is an area of ongoing investigation. Temporal bone histopathologic studies done at autopsy of patients with CS are characterized by chronic inflammation including: infiltration of the spiral ligament with lymphocytes and plasma cells, endolymphatic hydrops, degenerative changes in the organ of Corti, and demyelination and atrophy of the vestibular and cochlear branches of the eight cranial nerve.

There is no criteria currently established for the diagnosis of CS. The general thinking is that the diagnosis requires clinical signs of both eye and inner ear inflammation. Work-up should include an audiogram and laboratory tests including CBC, ESR, and RPR. Imaging including MRI and/or CT should be done primarily to rule out cerebropontine angle tumors and other disorders. MRI may show enhancement of vestibular and cochlear structures with gadolinium.

The cornerstone of therapy is corticosteroids: topical for IK and oral for vestibuloauditory involvement. Most authors suggest using prednisone 1mg/kg for 2-4 weeks with a subsequent rapid taper for cases of complete resolution and slow taper for those with incomplete response. The best outcome is in patients in whom therapy begins shortly after the onset of symptoms. For patients who have failed steroid treatment and developed bilateral deafness, cochlear implantation should be considered and has been approved by the FDA in these patients.

Traumatic

Traumatic breaks in the membranous labyrinth are accepted causes of sudden hearing loss. Cochlear membrane breaks may be either intracochlear, as is thought to occur in Meniere’s disease, or involve the labyrinthine oval and/or round windows with a resultant perilymph fistula. The patients history will usually elicit an inciting event such as a blow to the head, sneezing, bending over, lifting a heavy object, exposure to sudden changes in barometric pressure (such as during flying or diving), or exposure to a loud noise. Patients who are theoretically at high risk for fistulization are those who have undergone anatomical alterations such as stapedectomy patients and in children with inner ear anomalies, such as the Mondini malformation and large vestibular aqueducts where increases in CSF pressure may be transmitted to the inner ear more easily. In clinical practice, however, patients who have undergone stapedectomy who return to their normal lifestyles including scuba diving and flying have not resulted in an obvious increase in development of symptoms of perilymphatic fistulas.

Currently there is no definitive test to diagnose perilymph fistulae other than intraoperative observation of leakage of perilymph. Diagnosis is made by the clinical history of sudden or rapidly progressive hearing loss after one of the above listed inciting events. Inflammation, granuloma, or neoplasia disorders that can mimic a perilymph fistula should be ruled out (i.e. with MRI, MHATP, and ESR). Kohut proposes that two of the following vestibular symptoms are required for diagnosis: constant dysequilibrium, a positive fistula test (Hennebert’s sign), and a positional nystagmus. Testing for Tullio’s phenomenon should also be done.

Posted 6/15/2001
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