Sensorineural hearing loss is a complex disease state influenced by genetics, age, noise, and many other factors. This article reviews our current knowledge regarding the causes of sensorineural hearing loss and reviews the more challenging clinical presentations of sensorineural hearing loss. We have reviewed the latest medical literature in an attempt to provide an evidence-based strategy for the assessment and management of sudden sensorineural hearing loss, rapidly progressive sensorineural hearing loss, and asymmetric/unilateral sensorineural hearing loss.
The following points list the level of evidence based on the criteria of the Oxford Center for Evidence-Based Medicine. Additional critical points are provided and points here are expanded at the conclusion of this article.
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The best current evidence for oral corticosteroid treatment of sudden sensorineural hearing loss (SSNHL) is contradictory in outcome and does not permit a definitive treatment recommendation (level 1a).
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Treatment of SSNHL may be equally efficacious up to and potentially later than 10 days after the loss of hearing (level 1b).
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Transtympanic corticosteroids may be useful as either primary therapy or salvage therapy in patients with medical comorbidities who are at risk of serious adverse effects from oral corticosteroid administration (level 1b).
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There is insufficient evidence to recommend antiviral therapy as primary or steroid adjunctive therapy in patients with SSNHL (level 1a).
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There is limited evidence to suggest that primary hyperbaric oxygen therapy improves hearing in patients with idiopathic SSNHL and no evidence of a functionally significant improvement (level 1a).
Overview
Sensorineural hearing loss (SNHL) is a complex disease influenced by interactions between multiple internal and external causative factors. Genetics and age-related hearing changes may predetermine a patient’s hearing throughout their lifetime, and any potential hearing changes over time may be accelerated by numerous external factors. This relationship becomes particularly complex if the patient’s genetic makeup predisposes that individual to a hearing vulnerability from external influences such as chronic exposure to traumatic levels of noise or from the use of ototoxic pharmaceuticals.
The complexity of the diagnostic evaluation and potential treatment options for SNHL has increased because of multiple considerations. There is a downward trend in the presenting age and an increasing severity of hearing loss in patients from first-world (industrialized) nations. Patterns of hearing loss have changed in relation to noise exposure because of various occupational hazards such as heavy industrial noise and firearms use in military and police occupations. Clinicians involved in the management of critically ill and complex medical patients are aware of the impact that pharmaceutical therapy for multisystem disease may have on hearing. Patients who have immigrated from developing countries may present with hearing loss caused by exposure to rare pathogens such as Lassa fever or with a chronic otitis media complicated by a lack of primary care or access to an otolaryngologist in their country of origin. Thus, it is prudent for any practicing otolaryngologist to be aware of these and other factors that may influence their diagnostic and management approaches for patients presenting with SNHL.
The medical literature contains thousands of research papers on SNHL, the overall aim of which is to improve our ability as clinicians to diagnose and treat patients with hearing loss. The challenge lies in sifting through this wealth of data and applying them to our everyday practices, because the principles of evidence-based medicine have become integrated into our daily clinical interaction with patients. The goal of this article is to present the current best evidence available regarding the diagnostic process and treatments available for the management of hearing loss as it applies to the more controversial aspects of adult SNHL. The levels of evidence proposed by the Oxford Center for Evidence-Based Medicine are used throughout this article.
Causes of Sensorineural Hearing Loss
Presbycusis is the most common cause of SNHL in industrialized nations. In 2003 to 2004, the prevalence of hearing loss in the adult US population aged 20 to 69 years was 16.1% (29 million Americans), and 31% of those had a high-frequency hearing loss. The prevalence of hearing loss was higher among the following set of individuals :
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Men
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White
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Older age
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Less educated
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History of diabetes mellitus
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History of hypertension
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Greater than a 20 pack-year history of smoking
It can be expected that the prevalence and impact of hearing loss on society will increase as the elderly proportion of the population in many industrialized nations continues to grow.
Noise
The detrimental effect of noise on the inner ear is one of the most common causes of permanent hearing loss. Approximately 30 million American workers are exposed to hazardous work-related noise. Occupational and recreational exposure to firearms is also a significant cause of permanent noise-induced hearing loss. Permanent damage from firearms use in police officers was identified in a long-term study, even with the regular use of dual hearing protection. Despite the increasing prevalence of hearing loss in the general population because of noise, this resultant hearing loss is preventable through engineering controls or with the use of regular and habitual hearing protection.
Heredity and environment
Hereditary and developmental factors play a key role in influencing the development of SNHL. Multiple reviews have been published summarizing the complex role of genetics and hearing loss. Dozens of genetic loci have been identified as the causes of numerous syndromic and nonsyndromic hearing loss with variable inheritance patterns (autosomal-dominant, autosomal-recessive, X-linked, mitochondrial). Genetic loci have been also identified that increase the potential for permanent SNHL caused by noise trauma or ototoxic medications such as aminoglycoside antibiotics. Hearing losses caused by developmental disorders of the inner ear have also been linked to:
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Spontaneous or inherited genetic abnormalities, such as complete (Michel) aplasia
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Cochlear anomalies such as a Mondini malformation, labyrinthine anomalies, and ductal anomalies (enlarged vestibular aqueduct)
Infection
SNHL is a known complication of otologic or central nervous system infections such as acute labyrinthitis, meningitis, or as a sequela of chronic suppurative otitis media. Pediatric SNHL has been linked to multiple congenital infections such as toxoplasmosis and syphilis. Labyrinthitis ossificans and permanent SNHL is a known sequela of bacterial meningitis.
Vascular
Vascular interruption of labyrinthine blood flow is another common suspected cause of SNHL, typically seen in an acute fashion after a cerebrovascular accident, acute interruption of posterior cerebral circulation, or as the result of a coagulopathy or other hematologic anomaly. Several studies have examined the relationship between sudden SNHL (SSNHL) and cardiovascular and thrombophilic risk factors.
Ototoxicity
Ototoxicity is a well-established complication of drug administration. The hearing loss can be reversible or permanent and can be accompanied by other otologic symptoms such as tinnitus and vertigo. Cisplatin chemotherapeutic agents, aminoglycoside antibiotics, and loop diuretics are frequently cited as the most common medications that can damage the inner ear. Critically ill patients are at particular risk of ototoxicity as a result of renal and hepatic compromise and the use of multiple ototoxic agents. Ototoxicity can also occur from the instillation of ototopical drops in the presence of a ventilation tube or tympanic membrane perforation.
Trauma
Trauma to the ear and temporal bone are uncommon causes of SNHL. Fractures involving the otic capsule may result in permanent SNHL, vertigo, and facial nerve injury. Inner ear barotrauma from scuba diving or sudden and violent pressure changes to the external and middle ear causing damage to the oval or round windows may result in perilymph fistulization and subsequent hearing loss, tinnitus, and vertigo.
Autoimmune ear disease
Autoimmune inner ear disease (AIED) was first described in the medical literature in 1979, and involvement of the inner ear in autoimmune disease has since become well established. Autoantibodies that target inner ear–specific antigens have been identified, and numerous studies have confirmed the association between SNHL and systemic autoimmune diseases such as Cogan syndrome, rheumatoid arthritis, systemic lupus erythematosus, and Wegener granulomatosis.
Neoplastic disease
Neoplastic disease of the cerebellopontine angle (CPA) can present with a progressive or sudden onset of hearing loss and other otologic symptoms; vestibular schwannoma is the most common diagnosis. Early identification of CPA tumors poses a challenging diagnostic dilemma for otolaryngologists, and is discussed further in this article. Metastatic disease involving the temporal bone may also present in a similar clinical fashion to a CPA tumor.
Endolymphatic hydrops and central nervous system disease
Although many other causes of SNHL exist, only 2 other causes are noted here. Endolymphatic hydrops is a primary otologic cause of SNHL, the cause of which remains in dispute. The classic presentation of Ménière syndrome (tinnitus, aural fullness, hearing loss, and peripheral vertigo) can often present as SSNHL or fluctuating SNHL affecting 1 or both ears. The diagnostic process can be challenging and prolonged before the diagnosis is made, usually after other more acute or life-threatening causes have been ruled out. Central nervous system disease such as cerebrovascular accidents or multiple sclerosis can also cause varying degrees of SNHL, which can be rapidly progressive, sudden, asymmetric, or bilateral.
Sudden Sensorineural Hearing Loss
SSNHL remains a diagnostic and therapeutic dilemma. Many aspects of this clinical entity are disputed in the medical literature, such as the definition of the syndrome, cause and clinical investigations, therapeutic interventions, and spontaneous rate of recovery. SSNHL is considered an otologic emergency primarily for expeditious treatment with corticosteroids as soon as possible after the onset of hearing loss. However, both the use of corticosteroids for sudden hearing loss and its status as an otologic emergency are under dispute.
SSNHL is characterized by a rapid deterioration in hearing over seconds to days, with no universally accepted clinical definition. The most common definition in the literature is as defined by the National Institute on Deafness and Other Communications Disorder: an SNHL of 30 dB or more across at least 3 contiguous frequencies occurring within 72 hours. Regional global variations in SSNHL definition exist, and numerous other criteria have been used for defining SSNHL in the literature. The incidence of SSNHL has been estimated by Byl to range between 5 and 20 cases per 100,000 persons per year, but some consider this estimate to be lower than the actual number of cases because it is suspected that many cases of SSNHL resolve spontaneously before presentation to a hospital or physician. Most cases of SSNHL are unilateral, with bilateral involvement uncommon and simultaneous bilateral involvement rare. Factors that may influence the prognosis for hearing recovery include the age of the patient, severity and type of hearing loss, time between hearing loss onset and treatment, and presence of vertigo.
The cause of SSNHL was reviewed by the senior author. The identifiable suspected causes included infectious disease in 12.8%, primary otologic disease in 4.7%, temporal bone and inner ear trauma in 4.2%, vascular or hematologic causes in 2.8%, neoplastic disease in 2.3%, and other causes in 2.2% of patients. Seventy-one percent of patients reviewed suffered from an idiopathic SSNHL, and it is these idiopathic cases that drive continuing research regarding sudden hearing loss.
Asymmetric/Unilateral Sensorineural Hearing Loss
The goal of evaluation for an asymmetric SNHL (ASNHL) is to rule out a retrocochlear cause such as vestibular schwannoma. Historically, clinicians relied on audiometric tests to identify patients with a retrocochlear pattern of disease and follow-up with a computed tomography (CT) scan. Advancements in technology have shifted our diagnostic reliance onto highly sensitive and specific diagnostic imaging tests such as magnetic resonance imaging (MRI), which can detect vestibular schwannomas at an early stage of presentation and potentially reduce the morbidity of any potential treatment. The high cost and limited availability of MRI in the past has influenced the development of cost-effective clinical diagnostic algorithms for asymmetric hearing loss evaluation. Refinements in MRI technology have allowed for more rapid acquisition of higher-resolution imaging at a reduced per-patient cost to the health care system. Despite these advancements, considerable debate continues regarding multiple factors such as the appropriate audiometric thresholds that should trigger radiographic evaluation of ASNHL as well as the continuing role of screening audiometric tests such as evoked auditory brainstem potentials to achieve a cost-effective evaluation.
Rapidly Progressive Sensorineural Hearing Loss
Rapidly declining or fluctuating SNHL presents in less than 1% of patients presenting with hearing loss and is often considered synonymous with the diagnosis of an AIED. McCabe’s original article reviewed 18 patients who presented with variable bilateral audiovestibular disease that improved with oral corticosteroids and intravenous cyclophosphamide. Autoimmune hearing loss is typically not as rapid as an SSNHL, but is significantly more pronounced than would be associated with presbycusis. It is typically bilateral, asymmetric, and rapidly progressive over weeks to months.
Multiple ear diseases have been found to have a primary immunologic cause such as relapsing polychondritis, otosclerosis, Ménière disease, and sudden hearing loss. The ear can also be affected by systemic autoimmune diseases such as systematic lupus erythematosus, rheumatoid arthritis, Sjögren syndrome, Cogan syndrome, Wegener granulomatosis, and systemic sclerosis.
Evidence-based clinical assessment
A comprehensive history and physical examination are vital in the evaluation of a patient with hearing loss. The history should focus on the presence of other otologic symptoms such as tinnitus, vertigo, otalgia, aural fullness, and otorrhea, as well as a review of symptoms that assesses the status of the central nervous system. The patient’s past medical history, family history, medication profile, and social history should be taken into consideration. Known causative causes for hearing loss should be reviewed and thoroughly evaluated if identified as potential risk factors on history and physical examination.
The diagnostic evaluation of a patient with SSNHL is a significant source of debate in the medical literature. Diagnostic regimens for SSNHL workup vary significantly amongst clinicians and there is no standardized battery of tests. Many centers have reported their results using diagnostic batteries for SSNHL with varying results. Numerous research articles have been published examining various aspects of SSNHL diagnosis, such as medical risk factor profiles, genetic predisposition toward prothrombotic and hypercoagulable states, autoimmune markers, the presence of infectious disease markers, and the usefulness of diagnostic imaging studies for diagnosing SSNHL.
Audiometric Testing
Standard pure tone audiometry (0.25 kHz–8 kHz) and speech discrimination testing are not only required to provide the criteria for any hearing loss diagnosis, but the characteristics of the initial audiogram provide a baseline for comparison and may also provide prognostic value. Serial audiometric evaluations are necessary to document recovery, monitor treatment response, screen for relapse, guide aural rehabilitation, and rule out hearing loss in the contralateral ear. If malingering is suspected, a Stenger test should be performed to rule out pseudohypoacusis.
The definition of ASNHL is unclear in the literature. Many investigators have tried to validate a universal definition that can be clinically applied. Commonly cited definitions include: 15 dB or greater (0.25–8 kHz), 15 dB or greater at 2 or more frequencies or a 15% or greater difference in speech discrimination score, or 20 dB or greater at 2 consecutive frequencies. Saliba and colleagues proposed a Rule 3000 after finding that an asymmetry of 15 dB or more at 3000 Hz had the highest odds-ratio association with a positive vestibular schwannoma finding on MRI in their retrospective study population. Gimsing recently concluded that a patient with a 20-dB or greater asymmetry at 2 adjacent frequencies, unilateral tinnitus, or a 15-dB or greater asymmetry at 2 frequencies between 2 and 8 kHz on screening audiogram yielded the best compromise between sensitivity and specificity when attempting to rule out a vestibular schwannoma.
Auditory Brainstem Response
Auditory evoked potentials are commonly used for the detection of retrocochlear disease in asymmetric and sudden hearing loss. MRI has been shown to be a more sensitive diagnostic test for the detection of vestibular schwannoma than auditory brainstem response (ABR) (88% vs 99%), particularly for tumors measuring less than 1 cm in diameter (79%). For cases in which MRI is not available or contraindicated, ABR may prove to be a suitable but less sensitive alternative test. Don and colleagues showed improved sensitivity using stacked ABR (95%) in patients with vestibular schwannomas measuring less than 1 cm. The use of ABR for screening retrocochlear disease is also a less favorable diagnostic option from a practical standpoint, because sufficient residual hearing thresholds (<75 dbHL) must be present for an ABR response to be observed.
Vestibular Assessment
The presence of vertiginous symptoms with SSNHL is common and is generally believed to be a poor prognostic factor for hearing recovery. Objective vestibular assessment with electronystagmography (ENG) or vestibular evoked myogenic potentials (VEMP) testing is not a common part of an SSNHL test battery but may be useful in predicting the prognosis for hearing recovery. Korres and colleagues identified a significantly higher number of abnormal ENG and VEMP results in patients with profound hearing loss, as well as a negative correlation between the severity of hearing loss and the likelihood of hearing recovery. These findings are similar to previously published findings in the literature.
Magnetic Resonance Imaging
Radiologic evaluation of the CPA and internal acoustic meatus via MRI with gadolinium is indicated for the identification of potentially treatable causes of unilateral SSNHL and asymmetric hearing loss. The sensitivity and specificity of MRI with gadolinium in the diagnosis of a vestibular schwannoma larger than 3 mm approaches nearly 100%. Contrast-enhanced MRI can identify an abnormality in 10.7% to 57% of patients with SSNHL such as a CPA tumor, labyrinthine hemorrhage, cerebrovascular accident, or demyelinating process. In patients with renal compromise, the risk of nephrogenic systemic fibrosis may contraindicate the use of gadolinium (relative glomerular filtration rate [GFR], 60 mL/min; absolute GFR <30 mL/min). In such cases, high-resolution MRI with constructive interference steady state sequence may be performed instead.
Computed Tomography
Patients who are unable to receive an MRI scan (implanted ferromagnetic materials, claustrophobia) may undergo a CT scan with intravenous contrast of the head and temporal bones. Such scans have reasonable sensitivity for lesions greater than 1.5 cm in diameter, although remain suboptimal in their diagnostic capabilities for retrocochlear lesions when compared with MRI.
Laboratory Tests
The evaluation of patients with SSNHL with laboratory tests is variable. Laboratory tests including complete blood count, electrolytes, basic metabolic panels, and erythrocyte sedimentation rate (ESR) are deemed reasonable but many clinicians may decide to forgo even these measures because of their low yield. There is no evidence to support a shotgun approach to serologic testing for patients with SSNHL, because the positive yield of such testing remains unfavorably low. However, when the history and physical examination suggest a possible cause, such information should be used to guide further specific serologic workup.
Serologic markers for metabolic disorders are commonly investigated in patients with SSNHL. Hypercholesterolemia has been identified in 35% to 40% of patients with idiopathic SSNHL, and hyperglycemia in 18% to 37% of patients. Hypothyroidism is also common, with a prevalence of up to 15% in patients with SSNHL. Most of these conditions have been identified on previous testing performed by the primary care physician before presentation to an otolaryngologist. Patients without a previously known diagnosis of these disorders may benefit from a screening evaluation when presenting with SSNHL.
Hemostatic parameters such as thrombophilic genetic polymorphisms and coagulation studies have been investigated in patients with SSNHL. A higher rate of polymorphisms in factor V Leiden, prothrombin, methylenetetrahydrofolate reductase, and platelet GlyIIIa have been shown in patients with SSNHL, but our clinical ability to identify these polymorphisms in the general population to stratify or minimize the risk of an SSNHL event before its occurrence is not feasible. Ballesteros and colleagues showed that patients with SSNHL do not have a statistically significant difference in their coagulation profile compared with controls, suggesting that coagulation studies such as prothrombin time, activated partial thromboplastin time, and coagulation factors are of little diagnostic value in the clinical evaluation of SSNHL unless warranted by evidence of a systemic process by a comprehensive history and physical examination. Thus, the usefulness of routine evaluation of hemostatic parameters in SSNHL remains unlikely to provide significant clinical information that affects the incidence, therapy, or prognosis.
Infectious Diseases
Tests to identify possible infectious causes for SSNHL have been proposed in numerous diagnostic algorithms. Numerous studies have attempted to associate a viral cause with SSNHL. Influenza B and enterovirus have been shown to have higher rates of seroconversion in patients with SSNHL in some studies. Other studies have failed to show an association between SSNHL and human herpes simplex virus, varicella zoster, cytomegalovirus, influenza A1/A3, parainfluenza viruses 1, 2, and 3, enterovirus, cytomegalovirus, Epstein-Barr virus, hepatitis C, adenovirus, rubella, and respiratory syncytial virus. There is currently little evidence to support the use of routine shotgun screening for a viral cause using polymerase chain reaction or preconvalescent and postconvalescent immunoglobulin titers in the workup of SSNHL. Convincing evidence of a causal relationship between a viral infection and SSNHL is lacking, and these investigations have not been shown to make a significant difference in guiding treatment or providing a benefit to patient outcomes.
Screening tests for nonviral infectious should be performed if a patient’s history and physical examination are suggestive of an infectious cause. Hearing loss caused by Lyme disease rarely presents without other clinical symptoms, thus patients with history of exposure and positive clinical findings should be considered for serologic testing. Confirmation of Borrelia infection can be performed by enzyme-linked immunosorbent assay (ELISA) testing or a serum immunoblot test, which is more specific than ELISA for anti- Borrelia burgdorferi antibodies. If the possibility of congenital or latent syphilis is suspected, then screening should be performed with serum fluorescent treponemal antibody absorption or microhemagglutination- Treponema pallidum testing.
Autoimmune Inner Ear Disease
Serologic markers for autoimmune disease are often ordered during the workup of sudden and rapidly progressive or fluctuating SNHL. Increase of the ESR is commonly seen in patients with SSNHL, although recent studies refute the prognostic usefulness of this marker. Multiple studies have examined the relationship between SSNHL and various systemic autoimmune markers including antinuclear antibodies, rheumatoid factor, and anticardiolipin antibodies, all of which have been shown to be increased in patients with SSNHL. Increased levels of antiphosphatidylserine antibodies and antiendothelial cell autoantibodies as well as a decrease in tumor necrosis factor α levels and T-helper cell populations have been shown in patients with SSNHL. All of these tests lack specificity for the diagnosis of an autoimmune-mediated SNHL, and the results are often clinically unhelpful because there is no identifiable positive association between the increase of a nonspecific inflammatory marker and a positive response to corticosteroid treatment of SSNHL in the medical literature.
Researchers have also investigated antibody responses to specific inner ear proteins. The 68-kDa antigen suspected to be heat shock protein 70 (hsp70) and its relationship with AIED has been researched extensively. Heat shock proteins are commonly expressed in multiple body tissues and in both healthy individuals and various disease states, thus limiting its diagnostic value in AIED. Other potential inner ear antigens include cochlin, β-tectorin, choline transporterlike protein 2, and myelin protein Po. Routine testing for these antigens is not recommended, because the role of these inner ear antigens in AIED remains unclear.
Evidence-based clinical assessment
A comprehensive history and physical examination are vital in the evaluation of a patient with hearing loss. The history should focus on the presence of other otologic symptoms such as tinnitus, vertigo, otalgia, aural fullness, and otorrhea, as well as a review of symptoms that assesses the status of the central nervous system. The patient’s past medical history, family history, medication profile, and social history should be taken into consideration. Known causative causes for hearing loss should be reviewed and thoroughly evaluated if identified as potential risk factors on history and physical examination.
The diagnostic evaluation of a patient with SSNHL is a significant source of debate in the medical literature. Diagnostic regimens for SSNHL workup vary significantly amongst clinicians and there is no standardized battery of tests. Many centers have reported their results using diagnostic batteries for SSNHL with varying results. Numerous research articles have been published examining various aspects of SSNHL diagnosis, such as medical risk factor profiles, genetic predisposition toward prothrombotic and hypercoagulable states, autoimmune markers, the presence of infectious disease markers, and the usefulness of diagnostic imaging studies for diagnosing SSNHL.
Audiometric Testing
Standard pure tone audiometry (0.25 kHz–8 kHz) and speech discrimination testing are not only required to provide the criteria for any hearing loss diagnosis, but the characteristics of the initial audiogram provide a baseline for comparison and may also provide prognostic value. Serial audiometric evaluations are necessary to document recovery, monitor treatment response, screen for relapse, guide aural rehabilitation, and rule out hearing loss in the contralateral ear. If malingering is suspected, a Stenger test should be performed to rule out pseudohypoacusis.
The definition of ASNHL is unclear in the literature. Many investigators have tried to validate a universal definition that can be clinically applied. Commonly cited definitions include: 15 dB or greater (0.25–8 kHz), 15 dB or greater at 2 or more frequencies or a 15% or greater difference in speech discrimination score, or 20 dB or greater at 2 consecutive frequencies. Saliba and colleagues proposed a Rule 3000 after finding that an asymmetry of 15 dB or more at 3000 Hz had the highest odds-ratio association with a positive vestibular schwannoma finding on MRI in their retrospective study population. Gimsing recently concluded that a patient with a 20-dB or greater asymmetry at 2 adjacent frequencies, unilateral tinnitus, or a 15-dB or greater asymmetry at 2 frequencies between 2 and 8 kHz on screening audiogram yielded the best compromise between sensitivity and specificity when attempting to rule out a vestibular schwannoma.
Auditory Brainstem Response
Auditory evoked potentials are commonly used for the detection of retrocochlear disease in asymmetric and sudden hearing loss. MRI has been shown to be a more sensitive diagnostic test for the detection of vestibular schwannoma than auditory brainstem response (ABR) (88% vs 99%), particularly for tumors measuring less than 1 cm in diameter (79%). For cases in which MRI is not available or contraindicated, ABR may prove to be a suitable but less sensitive alternative test. Don and colleagues showed improved sensitivity using stacked ABR (95%) in patients with vestibular schwannomas measuring less than 1 cm. The use of ABR for screening retrocochlear disease is also a less favorable diagnostic option from a practical standpoint, because sufficient residual hearing thresholds (<75 dbHL) must be present for an ABR response to be observed.
Vestibular Assessment
The presence of vertiginous symptoms with SSNHL is common and is generally believed to be a poor prognostic factor for hearing recovery. Objective vestibular assessment with electronystagmography (ENG) or vestibular evoked myogenic potentials (VEMP) testing is not a common part of an SSNHL test battery but may be useful in predicting the prognosis for hearing recovery. Korres and colleagues identified a significantly higher number of abnormal ENG and VEMP results in patients with profound hearing loss, as well as a negative correlation between the severity of hearing loss and the likelihood of hearing recovery. These findings are similar to previously published findings in the literature.
Magnetic Resonance Imaging
Radiologic evaluation of the CPA and internal acoustic meatus via MRI with gadolinium is indicated for the identification of potentially treatable causes of unilateral SSNHL and asymmetric hearing loss. The sensitivity and specificity of MRI with gadolinium in the diagnosis of a vestibular schwannoma larger than 3 mm approaches nearly 100%. Contrast-enhanced MRI can identify an abnormality in 10.7% to 57% of patients with SSNHL such as a CPA tumor, labyrinthine hemorrhage, cerebrovascular accident, or demyelinating process. In patients with renal compromise, the risk of nephrogenic systemic fibrosis may contraindicate the use of gadolinium (relative glomerular filtration rate [GFR], 60 mL/min; absolute GFR <30 mL/min). In such cases, high-resolution MRI with constructive interference steady state sequence may be performed instead.
Computed Tomography
Patients who are unable to receive an MRI scan (implanted ferromagnetic materials, claustrophobia) may undergo a CT scan with intravenous contrast of the head and temporal bones. Such scans have reasonable sensitivity for lesions greater than 1.5 cm in diameter, although remain suboptimal in their diagnostic capabilities for retrocochlear lesions when compared with MRI.
Laboratory Tests
The evaluation of patients with SSNHL with laboratory tests is variable. Laboratory tests including complete blood count, electrolytes, basic metabolic panels, and erythrocyte sedimentation rate (ESR) are deemed reasonable but many clinicians may decide to forgo even these measures because of their low yield. There is no evidence to support a shotgun approach to serologic testing for patients with SSNHL, because the positive yield of such testing remains unfavorably low. However, when the history and physical examination suggest a possible cause, such information should be used to guide further specific serologic workup.
Serologic markers for metabolic disorders are commonly investigated in patients with SSNHL. Hypercholesterolemia has been identified in 35% to 40% of patients with idiopathic SSNHL, and hyperglycemia in 18% to 37% of patients. Hypothyroidism is also common, with a prevalence of up to 15% in patients with SSNHL. Most of these conditions have been identified on previous testing performed by the primary care physician before presentation to an otolaryngologist. Patients without a previously known diagnosis of these disorders may benefit from a screening evaluation when presenting with SSNHL.
Hemostatic parameters such as thrombophilic genetic polymorphisms and coagulation studies have been investigated in patients with SSNHL. A higher rate of polymorphisms in factor V Leiden, prothrombin, methylenetetrahydrofolate reductase, and platelet GlyIIIa have been shown in patients with SSNHL, but our clinical ability to identify these polymorphisms in the general population to stratify or minimize the risk of an SSNHL event before its occurrence is not feasible. Ballesteros and colleagues showed that patients with SSNHL do not have a statistically significant difference in their coagulation profile compared with controls, suggesting that coagulation studies such as prothrombin time, activated partial thromboplastin time, and coagulation factors are of little diagnostic value in the clinical evaluation of SSNHL unless warranted by evidence of a systemic process by a comprehensive history and physical examination. Thus, the usefulness of routine evaluation of hemostatic parameters in SSNHL remains unlikely to provide significant clinical information that affects the incidence, therapy, or prognosis.
Infectious Diseases
Tests to identify possible infectious causes for SSNHL have been proposed in numerous diagnostic algorithms. Numerous studies have attempted to associate a viral cause with SSNHL. Influenza B and enterovirus have been shown to have higher rates of seroconversion in patients with SSNHL in some studies. Other studies have failed to show an association between SSNHL and human herpes simplex virus, varicella zoster, cytomegalovirus, influenza A1/A3, parainfluenza viruses 1, 2, and 3, enterovirus, cytomegalovirus, Epstein-Barr virus, hepatitis C, adenovirus, rubella, and respiratory syncytial virus. There is currently little evidence to support the use of routine shotgun screening for a viral cause using polymerase chain reaction or preconvalescent and postconvalescent immunoglobulin titers in the workup of SSNHL. Convincing evidence of a causal relationship between a viral infection and SSNHL is lacking, and these investigations have not been shown to make a significant difference in guiding treatment or providing a benefit to patient outcomes.
Screening tests for nonviral infectious should be performed if a patient’s history and physical examination are suggestive of an infectious cause. Hearing loss caused by Lyme disease rarely presents without other clinical symptoms, thus patients with history of exposure and positive clinical findings should be considered for serologic testing. Confirmation of Borrelia infection can be performed by enzyme-linked immunosorbent assay (ELISA) testing or a serum immunoblot test, which is more specific than ELISA for anti- Borrelia burgdorferi antibodies. If the possibility of congenital or latent syphilis is suspected, then screening should be performed with serum fluorescent treponemal antibody absorption or microhemagglutination- Treponema pallidum testing.
Autoimmune Inner Ear Disease
Serologic markers for autoimmune disease are often ordered during the workup of sudden and rapidly progressive or fluctuating SNHL. Increase of the ESR is commonly seen in patients with SSNHL, although recent studies refute the prognostic usefulness of this marker. Multiple studies have examined the relationship between SSNHL and various systemic autoimmune markers including antinuclear antibodies, rheumatoid factor, and anticardiolipin antibodies, all of which have been shown to be increased in patients with SSNHL. Increased levels of antiphosphatidylserine antibodies and antiendothelial cell autoantibodies as well as a decrease in tumor necrosis factor α levels and T-helper cell populations have been shown in patients with SSNHL. All of these tests lack specificity for the diagnosis of an autoimmune-mediated SNHL, and the results are often clinically unhelpful because there is no identifiable positive association between the increase of a nonspecific inflammatory marker and a positive response to corticosteroid treatment of SSNHL in the medical literature.
Researchers have also investigated antibody responses to specific inner ear proteins. The 68-kDa antigen suspected to be heat shock protein 70 (hsp70) and its relationship with AIED has been researched extensively. Heat shock proteins are commonly expressed in multiple body tissues and in both healthy individuals and various disease states, thus limiting its diagnostic value in AIED. Other potential inner ear antigens include cochlin, β-tectorin, choline transporterlike protein 2, and myelin protein Po. Routine testing for these antigens is not recommended, because the role of these inner ear antigens in AIED remains unclear.
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