Clinical manifestations

Presentation and course

By definition, the principal manifestation of sudden hearing loss is sensorineural hearing loss occurring over less than three days (92). It is usually a monophasic illness, but recurrences can occur with some etiologies (92). Depending on the etiology and on damage to associated structures, associated manifestations may include aural fullness or pressure, tinnitus, vertigo, nausea and vomiting, and various brainstem and cerebellar signs (92). In patients with sudden sensorineural hearing loss (SSNHL), tinnitus is associated with worse high-frequency hearing loss, whereas aural fullness and pressure sensations are typically associated with low-frequency hearing loss (156). Tinnitus and aural fullness improve with improvements in hearing (70).

Men and women are generally affected with equal frequency, although one study found a higher frequency among females than males (92; 129). The condition occurs most commonly in the fifth and sixth decades. For unknown reasons, the left ear is affected slightly more often than the right ear (151). The putative cause is identified in about 10% to 15% of cases, and the remainder is considered idiopathic after evaluation. Only a small minority (approximately 1%) has an identified retro-cochlear cause (eg, vestibular schwannoma, demyelinating disease, stroke) (148; 59).

Putative risk factors for sudden sensorineural hearing loss include cardiovascular risk factors (smoking, increased alcohol consumption), obstructive sleep apnea (in men only), and recent subclinical viral or toxoplasmosis infections (78; 107; 165).

Sudden deafness may be caused by ischemia of the cochlea or eighth nerve (92). Cochlear ischemia may occur in isolation, in conjunction with labyrinthine ischemia, or in conjunction with brainstem and cerebellar ischemia as a result of involvement of the anterior inferior cerebellar artery or the vertebrobasilar system (92). The constellation of clinical manifestations depends on the extent and distribution of the ischemia. The clinical manifestations of ischemia of the inner ear can include unilateral deafness and tinnitus as well as acute vertigo, nausea and vomiting, imbalance, and canal paresis (119; 116; 46; 54; 117; 118; 134; 80; 175; 194; 146; 92). Patients with involvement of the common cochlear artery may present with deafness and vestibular involvement limited to paresis of the posterior semicircular duct (146). In those with predominant auditory dysfunction, patients may present with sudden deafness (46; 186), sometimes accompanied by transient dizziness and intermittent tinnitus (46; 54). Mitral valve prolapse, mitral leaflet thickening, mitral regurgitation, and left atrial enlargement are risk factors for “idiopathic” sudden sensorineural hearing loss, and presumably these associations reflect an increased risk of cochlear or eighth nerve ischemia (183).

The spectrum of clinical presentation of anterior inferior cerebellar artery infarction includes ipsilateral hearing loss with or without tinnitus as well as a range of labyrinthine, brainstem, and cerebellar symptoms and signs (92). Other manifestations include ipsilateral Horner syndrome (rare), skew deviation (rare), nystagmus, ipsilateral facial numbness, ipsilateral facial paresis, vertigo, dysarthria, vomiting, unsteadiness, ipsilateral hemiataxia, and contralateral loss of pain and temperature sensation on the limbs and body (06; 62; 134; 07; 94; 92). Occasionally, isolated vertigo or isolated auditory disturbance may occur as transient ischemic attacks preceding anterior inferior cerebellar artery-territory infarction, or with partial infarcts (134; 07; 96; 105). Bilateral sudden deafness may occur as a prodrome of anterior inferior cerebellar artery-territory infarction in the presence of severe vertebrobasilar occlusive disease (98; 180). Rarely, the internal auditory artery branches off the posterior inferior cerebellar artery (rather than anterior inferior cerebellar artery) and sudden unilateral deafness may, therefore, result from posterior inferior cerebellar artery infarction (eg, with vertebral artery dissection) (150; 93).

The spectrum of clinical presentation of superior cerebellar artery syndrome includes ipsilateral Horner syndrome, ipsilateral limb ataxia, contralateral sensorineural hearing loss (due to involvement of the lateral lemniscus carrying decussated ascending auditory information), contralateral superficial sensory loss, vertigo, nystagmus, nausea, and vomiting (124).

Hearing loss occurs in about one fifth of patients with vertebrobasilar insufficiency and vertigo (194). Deafness associated with vertebrobasilar insufficiency mainly involves the cochlea, rather than central auditory pathways (194; 95). Tinnitus and vertigo are frequent accompaniments, as are a wide a range of brainstem and cerebellar symptoms and signs (100; 159).

Ischemia may also occur with vascular obstruction in the venules and capillaries, draining the inner ear, as occurs most commonly with conditions that produce marked serum hyperviscosity. The "hyperviscosity syndrome" includes a number of diverse clinical manifestations including headache, fatigue, vertigo, nystagmus, sudden or progressive hearing loss, visual disturbances, and mucosal hemorrhages (133; 08). Ophthalmoscopic findings include markedly distended and tortuous ("sausage-shaped") retinal veins and retinal hemorrhages, similar to the pattern seen in retinal vein occlusion.

Fabry disease, an X-linked lysosomal storage disorder due to alpha-galactosidase-A deficiency, is associated with auditory manifestations, including hearing loss, sudden deafness, and tinnitus (27).

Ramsay Hunt syndrome (herpes zoster oticus) may be associated with vesicles in the external auditory canal, burning pain in the ear, unilateral Bell palsy, unilateral hearing loss, tinnitus, vertigo, and transient spontaneous nystagmus.

With viral neurolabyrinthitis, autoimmune hearing loss, and Ménière syndrome, the clinical manifestations are primarily otologic, whereas hearing loss, tinnitus, vertigo, and spontaneous nystagmus are the predominant manifestations. No neurologic manifestations are present, apart from those attributable to the labyrinth and eighth nerve.

Viral neurolabyrinthitis may be part of a systemic viral illness or it may be an isolated viral infection of the labyrinth and eighth nerve. Many patients report an upper respiratory illness within 1 week or 2 weeks prior to the onset of symptoms. The manifestations are unilateral, and may include clinically evident aural or vestibular symptoms, or both (69). When hearing loss is incomplete, it is usually most severe at high frequencies. Some cases may develop posterior semicircular canal benign paroxysmal positional vertigo with preservation of lateral semicircular canal function (76).

Autoimmune hearing loss is often fluctuating, sometimes slowly progressive, and occasionally sudden. It may begin on one side, but invariably becomes bilateral. It may be associated with vertigo, if the involvement is sufficiently rapid and asymmetric. Often, a history of polyarteritis, rheumatoid arthritis, ulcerative colitis, Crohn disease, or other autoimmune-mediated conditions is present. Systemic manifestations may include interstitial keratitis, arthritis, rash, or gastrointestinal symptoms.

Ménière syndrome is associated with fluctuating sensorineural hearing loss, subjective tinnitus, aural fullness, episodic vertigo, and horizontal or horizontal-rotatory nystagmus. Onset may occur fairly suddenly over seconds, or it may develop over minutes or hours. The duration of hearing loss is variable among patients with some patients having this symptom for hours, others for days or weeks, and others permanently. Even with hearing recovery with continued episodes, recovery is often less complete, resulting in a progressive hearing loss. Involvement is typically unilateral at onset, but may become bilateral.

Sudden deafness can occur because of head trauma, but other manifestations of such injuries typically predominate, especially in the acute period. Rarely, sudden deafness can occur as a relatively isolated phenomena following modest trauma. For example, Lee and colleagues reported a case of sudden, bilateral deafness associated with bilateral pneumolabyrinth, without temporal bone fracture, after a fall (99).

Sudden deafness can rarely be due to sudden-onset cortical deafness from bilateral temporal lobe infarcts (12; 125; 104). The auditory cortex is located in the posterior superior aspect of both temporal lobes, with the primary auditory cortex located in the transverse temporal gyri of Heschl. Cortical deafness may evolve to auditory agnosia (ie, impairment of the ability to interpret both verbal and nonverbal sounds even though the patient can hear them) (12) or word deafness (ie, impairment of the ability to understand speech) (125).

Bilateral sudden deafness may occur due to cerebral hemorrhage or infarction (39). In a case series of 12 Chinese patients with bilateral sudden deafness following intracranial hemorrhage or infarction, the responsible loci varied: basal ganglia hemorrhage (n=7), cerebellar hemorrhage (n=2), temporal lobe hemorrhage (n=1), thalamic infarction (n=1), and pontine hemorrhage (n=1). Five patients partially or fully recovered hearing. The cause of hearing loss in these patients was attributed to the ischemia or other damage to the central hearing conduction pathways.

Prognosis and complications

The overall prognosis depends on the underlying etiology, but a high rate of spontaneous resolution occurs overall (ie, about two thirds of cases) (41; 195; 139; 171; 92). The rate of complete recovery and the recovery rate from profound hearing loss are significantly higher in children than in adults (126). One retrospective case series of pediatric cases found that the childhood group (ages 4 to 12) had worse treatment outcomes than the adolescence group (greater than 12 years of age) (81) and another uncontrolled study reported that adolescent patients fared worse (ie, less likely to recover hearing or improve tinnitus) than adult patients with combination therapy (176).

Most patients show either initial rapid recovery or a gradual and slow recovery (56), but the spontaneous recovery that occurs typically is within the first two weeks after onset (111). Maximum recovery of speech discrimination occurs by one year after symptom onset (132). Improvement in hearing levels tends to occur mostly in the low to mid frequencies and is better in those with preserved otoacoustic emissions (70).

Those with initial rapid recovery have the best prognosis, with a smaller degree of hearing loss at the first examination, greater degree of hearing improvement, and smaller degree of residual hearing loss once stable (56). Patients with upsloping or with lower or middle frequency hearing loss generally have a better prognosis (41; 198). Putative negative prognostic factors include longer time since onset of symptoms before treatment, more severe hearing loss, flat or downsloping audiograms, tinnitus, vertigo or evidence of vestibular dysfunction by neuro-otological studies (eg, vestibular evoked myogenic potentials and caloric testing), high signals in the affected inner ear on 3D-FLAIR MRI, very young or very old age, elevated sedimentation rate, and associated diabetes (123; 41; 198; 189; 89; 154; 178), but not all reports agree (44; 198; 148). Variation between reports depends in part on the method of outcome assessment, variation in patient characteristics including degree of hearing loss, and variation in adjustment for degree of hearing loss when considering recovery or improvement (41).

Audiovestibular residua or late effects can also include tinnitus, dysequilibrium, benign paroxysmal positioning vertigo, and Ménière syndrome (197; 69; 76; 148; 20). Annoying tinnitus and residual vertigo are the strongest predictors of the negative effects on quality of life in patients with sudden deafness (20).

Hematologic indices may be a helpful biomarker in gauging prognosis. Metaanalyses have found that the neutrophil-to-lymphocyte ratio, the platelet-to-lymphocyte ratio, the neutrophil count, and the lymphocyte count are all strongly associated with the prognosis of sudden sensorineural hearing loss (19; 26). Higher values on the neutrophil-to-lymphocyte ratio, the platelet-to-lymphocyte ratio, and the neutrophil count were predictive of worse outcomes, whereas higher lymphocyte counts were predictive of better outcomes (19; 26).

In isolated inner ear infarction, the vertigo, nystagmus, and autonomic manifestations resolve over days to weeks, but deafness and canal paresis typically remain (117; 118; 186; 80). If no brainstem symptoms develop and brain imaging is normal, the risk of recurrence or subsequent stroke is rare (117; 118; 80). Patients with labyrinthine ischemia due to vertebrobasilar insufficiency can have an overall good prognosis with anticoagulation or antiplatelet therapy (45) or, rarely, with surgical correction of a rotational vertebral artery syndrome (175). However, patients with inner ear infarction combined with brainstem or cerebellar infarcts have a worse prognosis (50), particularly if associated with occlusive disease of the basilar artery (42; 66).

Sudden sensorineural hearing loss is associated with an increased risk of subsequent stroke (106; 23; 90). In a cohort study, 13% of patients with sensorineural hearing loss had a stroke within five years, compared to 8% in controls, and after adjusting for other risk factors, those with sensorineural hearing loss had a risk of stroke 1.6 times greater than controls (106). Sudden hearing loss with vertigo is associated with a greater stroke risk than sudden hearing loss or vertigo alone (23).

Sudden sensorineural hearing loss can also result in later development of secondary endolymphatic hydrops with a mean interval of eight years (29).

Anxiety and depression are frequent in patients with sudden deafness (177).

Clinical vignette

A 66-year-old diabetic man developed bilateral deafness, right-sided tinnitus, and vertigo, which he noticed on rising in the morning (98). The vertigo resolved over the next day, but the hearing loss persisted. He had no visual field loss, diplopia, Horner syndrome, dysarthria, dysphagia, weakness, ataxia, or sensory loss. A week later he presented with worsened hearing loss in the right ear, right-sided tinnitus, vertigo, nausea, and incoordination. Examination demonstrated a spontaneous left-beating, horizontal-rotatory nystagmus; right facial hypesthesia; right peripheral facial palsy; and right-sided dysmetria. Audiometry showed moderate bilateral sensorineural hearing loss (55 dB on the right and 45 dB on the left) with 100% speech discrimination. Electronystagmography showed no response to caloric stimulation in the right ear. MRI demonstrated hyperintense foci on T2-weighted images involving the right dorsolateral pons and both middle cerebellar peduncles. MRA demonstrated moderately severe stenosis of the distal right vertebral artery and the middle third of the basilar artery. An electrocardiogram and a transthoracic echocardiogram were normal. The patient was anticoagulated. The vertigo and nausea improved over several days, and the right-sided incoordination and gait abnormalities improved over several weeks. A follow-up audiogram demonstrated profound hearing loss in the right ear and 30 dB loss in the left.

Biological basis

Anatomic localization

Sudden deafness may occur with interruption of peripheral or central structures involved with hearing. It most commonly occurs with damage to the cochlea or eighth nerve. Cochlear or eighth nerve infarction may occur in isolation or with concomitant infarction of the labyrinth, brainstem, and cerebellum (92). Acute bilateral hearing impairment suggests vertebrobasilar occlusive disease (66; 98; 79), but hearing loss associated with vertebrobasilar insufficiency is most frequently unilateral (194). Viral infections, inflammatory conditions, or autoimmune disorders that produce sudden hearing loss generally involve the labyrinth or eighth nerve. Ménière syndrome involves the labyrinth. Tumors (eg, acoustic neuromas) and meningitis that produce sudden hearing loss generally involve the eighth nerve. The frequent spontaneous recovery of hearing loss, and improvement with steroid therapy, suggest that in many cases there is a potentially reversible metabolic inner ear process disrupting the endocochlear potential, rather than immediate hair-cell degeneration (167).

Pathophysiology

The pathophysiology of sudden deafness is poorly understood, and it is likely that a variety of pathophysiologies can all produce sudden deafness. Various theories have been proposed, including those attributing sudden deafness to vascular insults, infectious (especially viral) agents, autoimmune or inflammatory mechanisms, or disruption of labyrinthine membranes (92). Despite extensive investigation, most cases remain idiopathic. Of the non-idiopathic cases, vascular and infectious etiologies are probably the most common, and the pathophysiology of these is best understood.

In the 1950s, a series of important experimental studies in animals established that cochlear function is extremely sensitive to anoxia (43; 82; 83; 84; 85; 142; 141). Obstruction of either the inferior cochlear vein or the internal auditory artery produces rapid loss of function; electrical activity deteriorates within 60 seconds of interruption of blood flow. Cochlear function may return to normal if blood flow is restored within 8 minutes of complete obstruction, but not if blood flow is interrupted for more than 30 minutes. External hair cells and the ganglion cells of the cochlea are particularly vulnerable to arterial obstruction, whereas the vestibular end organs are relatively resistant.

Venous drainage of the cochlea is via the vein of the cochlear aqueduct, which empties into the bulb of the jugular vein (10; 113). Venous obstruction produces early epithelial edema, followed by hemorrhage into the epithelium and perilymphatic and endolymphatic spaces, hair cell damage with secondary ganglion cell degeneration and, later, fibrosis and ossification. Labyrinthine ischemia, attributed to impaired venous drainage, most commonly results from hyperviscosity syndromes (121; 153; 133; 08; 155). Increased blood viscosity produces obstruction in the labyrinthine venules and capillaries with decreased blood flow and ischemia of the inner ear, subsequent hemorrhage and, later, fibrosis and ossification (82; 83). Similar changes occur in the eye producing visual disturbances, markedly distended and tortuous ("sausage-shaped") retinal veins, and retinal hemorrhages.

Arterial obstruction produces more rapid and severe damage than venous obstruction, whereas arterial obstruction produces histologically evident changes in hair cells within 30 minutes, followed in a few hours by extensive necrosis including the supporting cells without hemorrhage and, ultimately, severe fibrosis and ossification by six months. Several patterns of end organ involvement occur with arterial obstruction and correspond to involvement of different arterial distributions within the inner ear.

The blood supply to the inner ear is via the internal auditory artery (also called the labyrinthine artery), which typically originates from the anterior inferior cerebellar artery (10; 112; 113). The internal auditory artery divides into two main branches within the internal auditory canal: (1) the common cochlear artery and (2) the anterior vestibular artery (10; 113). The common cochlear artery divides into the main cochlear artery and the vestibulocochlear artery, which together supply the cochlea (10; 113). The internal auditory artery and its branches are end arteries, so even transient ischemia can cause permanent inner ear damage. The organ of Corti is particularly sensitive to ischemia (158).

The anterior inferior cerebellar artery supplies the lateral pons, the middle cerebellar peduncle, the flocculus, the anterior part of the cerebellar lobules, and the inner ear (06). In patients with anterior inferior cerebellar artery territory infarction, the most consistently involved areas are the lateral pons and the middle cerebellar peduncle (06). As a result of the sharp angulation of the anterior inferior cerebellar artery at its origin, it is rarely occluded by emboli (186); rather, most occlusions are due to either basilar artery plaques extending into the anterior inferior cerebellar artery or microatheroma of its origin (07). Whether isolated or in combination with other symptoms and signs, deafness and vertigo can occur in anterior inferior cerebellar artery -distribution infarctions due to involvement of several central and peripheral sites, which include the labyrinth, the eighth nerve, the vestibular nuclei, the vestibulocerebellum, or some combination.

Ramsay Hunt syndrome (herpes zoster oticus) is caused by reactivation of herpes zoster virus that had been dormant in the seventh and eighth nerves following previous infection with chicken pox. Pathologic findings in Ramsay Hunt syndrome include perivascular, perineural, and intraneural round-cell infiltration of the seventh and eighth nerves. A large number of other viruses have been associated with viral neurolabyrinthitis, but herpes simplex virus type 1 has been particularly associated with sudden sensorineural hearing loss (190; 145). Pathologic studies in patients with viral neurolabyrinthitis and sudden deafness have shown evidence of viral damage to the cochlea and auditory nerve, similar to that seen in patients with well-documented viral disorders (eg, mumps). Experimental animal studies have also demonstrated that several viruses can selectively infect the labyrinth and eighth nerve.

Genetic susceptibility may also be important in the pathogenesis of sudden deafness (25).

Differential diagnosis

Confusing conditions

Psychogenic sudden deafness can be identified by a discrepancy between behavioral hearing thresholds (eg, pure tone audiometry) and objective electrophysiologic examinations (eg, impedance audiometry, otoacoustic emissions, and brainstem auditory evoked responses) (13). Psychogenic sudden deafness can be unilateral or bilateral and generally ranges in severity from moderate hearing loss to profound hearing loss, with the majority having severe to profound hearing loss on pure-tone audiometry (13). It is most commonly reported in teenagers and young adults (13). Many have preexisting psychiatric illnesses or readily identified psychosocial stresses (13).

Associated or underlying disorders

Sudden hearing loss can be caused by a variety of disorders, including inner ear or eighth nerve ischemia, viral infection of the labyrinth or cochlear nerve, Ménière disease, intralabyrinthine membrane rupture, and autoimmune or inflammatory causes (172; 41; 182; 17; 108; 148; 61; 196; 92; 163). Uncommon causes include retrocochlear masses, demyelinating disease, syphilis, Lyme disease, Rickettsia felis infection, meningitis, carcinomatous meningitis, Takayasu arteritis, perilymph fistula, toxins, pregnancy, chronic sinusitis (especially in those aged 44 years or fewer), and prior radiation therapy for nasopharyngeal carcinoma (58; 60; 108; 73; 148; 136; 64; 77; 138; 21; 49; 92; 103; 131; 30; 68). Barotrauma, head injury (especially with temporal bone fracture, but also with inner ear concussion), and otologic surgery can also produce sudden heading loss, but these are rare and fairly obvious causes (152; 99).

The putative cause is identified in about 10% to 15% of cases, and the remainder is almost always unilateral and considered idiopathic after evaluation (148; 51). Only a small minority (approximately 1%) has an identified retrocochlear cause (eg, vestibular schwannoma, demyelinating disease, stroke) (148; 59). Rare bilateral cases may be due to malingering, conversion disorders, and neurologic causes (eg, vertebrobasilar occlusive disease, carcinomatous meningitis, paraneoplastic syndromes, encephalitis, meningitis), and polysubstance abuse or overdose (87; 148; 161; 168).

A variety of conditions can cause inner ear ischemia, including thromboemboli of the posterior circulation (53), migraine (97; 143), fat emboli (72), thromboangiitis obliterans (86), hyperlipidemia (155), macroglobulinemia (153; 133), sickle cell disease (Morgenstern and Manace 1969; 08), leukemia (08); polycythemia vera (08); other causes of hypercoagulation or hyperviscosity (72; 08), and hypotension in otherwise healthy young adults (144). Inner ear infarction occurs most commonly in the setting of thromboembolic disease of the anterior inferior cerebellar artery or the basilar artery (54; 62; 134; 66; 80; 184; 175; 97). Sudden deafness in anterior inferior cerebellar artery infarction is often due to cochlea dysfunction from ischemia (97), but mixed central and peripheral vestibular dysfunction also occurs, making recognition of the components difficult. Anterior inferior cerebellar artery territory infarction can be confused with posterior inferior cerebellar artery territory infarction (Wallenberg syndrome), because of shared signs including Horner syndrome, facial sensory impairment, vestibular signs, dysmetria, and contralateral impairment of pain and temperature sensation; however, severe facial paresis, hearing loss, and tinnitus are atypical for posterior inferior cerebellar artery territory infarctions (93), and their presence should alert the clinician to anterior inferior cerebellar artery territory infarction (06).

Various infectious disorders have been implicated in occasional cases of sudden hearing loss. A large number of viruses have been clinically, epidemiologically, or pathologically associated with hearing loss (65), but proof of viral etiology in individual cases is difficult to establish, with the exception of Ramsay Hunt syndrome where the clinical features are fairly obvious and characteristic. Furthermore, the Henle-Koch postulates have not been satisfied for establishing a viral causation for sudden sensorineural hearing loss (115). Bacterial meningitis, syphilis, Lyme disease, and Rickettsia felis infection are among other infectious etiologies implicated in sudden hearing loss (138; 131). Rickettsia felis is an emergent pathogen belonging to transitional group rickettsiae (140). First described in 1990, R felis infections can present with clinical signs similar to those of murine typhus and other febrile illnesses such as dengue fever, but like Lyme disease R felis infections can result in peripheral facial palsy and sudden deafness (138; 131). Cat fleas appear to be the most common vectors of R felis infections (140).

Although acoustic neuroma is a relatively rare cause of sudden hearing loss (less than 2% of patients with this problem) (41), sudden hearing loss may be the presenting symptom in 10% of patients to 15% of patients with acoustic neuroma (16; 41). In such patients, hearing may recover to normal levels with steroid therapy and may falsely suggest an inflammatory or immunologically mediated cause (16; 47). Other tumors can sometimes present with sudden hearing loss, and anecdotal reports include sudden hearing loss from a cochlear schwannoma (166). Sudden hearing loss may also complicate meningitis (40; 37), but it is rarely the presenting or only manifestation, except, in rare cases of chronic infectious, leukemic, or carcinomatous meningitis.

Sudden sensorineural hearing loss may also occur from medications, including nonsteroidal anti-inflammatory drugs (114), aminoglycosides, and phosphodiesterase inhibitors (14). Rapid ototoxic hearing loss is much more common in patients with poor renal function.

Sudden sensorineural hearing loss may be the initial presentation of Ménière disease, especially in patients with low-frequency hearing loss, or as a late manifestation years after onset (148). In those patients in whom sudden sensorineural hearing loss is the initial presentation, further fluctuation in hearing with attacks of vertigo are likely to develop within three years (148).

Sudden deafness can be an isolated symptom or the presenting symptom of a systemic disease.

Diagnostic workup

Initial evaluation of patients with presumptive sudden sensorineural hearing loss should include careful history and examination to identify bilateral sudden hearing loss, recurrent sudden hearing loss, or focal neurologic findings (170). In addition evaluation should identify likely toxic, otologic, or systemic causes, including evaluation of Lyme titers and syphilis serologies. Audiograms should also be obtained to demonstrate the pattern and severity of hearing loss, which are helpful prognostically. It is important to distinguish sensorineural and conductive patterns of hearing loss in patients with sudden hearing loss (170). Audiograms should be obtained before and within 24 to 48 hours after initiation of treatment. Current clinical practice guidelines specify that follow-up audiometric evaluation should be obtained within six months of diagnosis (170), and others suggest serial audiograms over the course of a year (eg, at 2, 6, and 12 months after onset) (148).

Patients with unilateral idiopathic sudden sensorineural hearing loss should be evaluated for retrocochlear pathology (eg, acoustic neuroma) using magnetic resonance imaging, brainstem auditory evoked potentials, or audiometric follow-up (170), whether or not apparent improvement or recovery is taking place (with or without steroid therapy) (162; 187; 01; 139; 147; 148). Cranial imaging is also important to exclude brainstem or cerebellar lesions (eg, vestibular schwannoma) (187; 01; 201), and MRI may identify a number of other pathologies (eg, vascular abnormalities, demyelination, hydrops, mastoiditis) (160; 01; 147; 201), but MRI does not visualize the inner ear well enough to reliably identify infarction and is insensitive for abnormalities (eg, enhancement) associated with cochleitis or labyrinthitis (173; 160). Inner ear MRI after intravenous gadolinium injection identifies abnormalities related to hearing in only about a quarter of cases (201). Approximately half of practicing otolaryngologists routinely utilize MRI in evaluating patients with sudden sensorineural hearing loss (31), and many neurologists routinely use this technology in the initial evaluation of patients with sudden sensorineural hearing loss, despite a low yield of identified retrocochlear pathology, because of medicolegal concerns (74). Current guidelines recommend against use of CT of the head and brain in the initial evaluation of patients with sudden sensorineural hearing loss (170), although in patients who cannot have an MRI, CT and brainstem auditory evoked potential studies should be considered, though these are less sensitive than MRI for detection of retrocochlear pathology (148).

As a result of a high rate of spontaneous recovery (approximately two thirds of cases), and because a large proportion of cases are ultimately considered to be idiopathic even after extensive evaluation, some have advocated a staged approach to diagnostic testing (34; 92). Patients with likely systemic causes or clinically evident neurologic abnormalities should have diagnostic testing without delay. In patients without other clinical findings, further diagnostic evaluation can possibly be delayed for a month to see if spontaneous improvement occurs. Note, though, that improvement with steroids (in the absence of MRI or brainstem auditory evoked responses) can result in failure to identify important clinical conditions, including acoustic neuroma. If improvement does not occur or if other symptoms or signs develop, more extensive diagnostic testing is indicated and should include cranial imaging with magnetic resonance imaging.

Additional diagnostic studies can include imaging of cerebral vessels, brainstem auditory evoked potentials, electronystagmography with bithermal caloric irrigation, vestibular-evoked myogenic potentials, lumbar puncture, and various blood studies. Brainstem auditory evoked potentials may show absence of wave I or all waveforms but may also show absence of wave I with delay of wave III and wave V, if dysfunction is also occurring in the retrocochlear eighth nerve and brainstem auditory nuclei and pathways (184). Electronystagmography or videonystagmography with bithermal caloric testing may demonstrate ipsilateral horizontal canal paresis. Vestibular-evoked myogenic potential studies may show an absence of response on the affected side, supporting labyrinthine damage, particularly in patients with associated vertigo (71; 146). Lumbar puncture should be performed (after cranial imaging) in immunocompromised patients and those with suspected chronic meningitis. In cases of clinically suspected sudden hearing loss resulting from hyperviscosity, the following blood studies can be considered: serum viscosity determination, complete blood count, syphilis serologies, sedimentation rate, serum protein, serum protein electrophoresis, and lipid studies. In cases of clinically suspected autoimmune inner ear disease, the following blood studies can be considered: sedimentation rate, rheumatoid factor, antinuclear antibody assay, antineutrophil cytoplasmic antibody assay, circulating immune complex levels, and urinalysis. Moreover, a number of more sophisticated immunologic tests of serological or cell-mediated reactivity to homologous and heterologous inner ear antigen extracts may have some utility but are not routinely available (57). Antibodies to a 68 kD heat shock protein (anti-hsp70) are not helpful (157). No correlation has been demonstrated between antibodies to inner ear antigens in patients with presumed autoimmune hearing loss and cochlear enhancement on MRI (199).

Management

Management is complicated as the underlying etiology is not known in most patients. A presumptive approach is generally employed, but no consensus exists concerning the management of sudden hearing loss (55; 31). Because of the lack of consensus, significant differences exist across specialists in the treatment of sudden sensorineural hearing loss (31).

Clinicians should not routinely prescribe antivirals, thrombolytics, vasodilators, vasoactive substances, or antioxidants to patients with idiopathic sudden sensorineural hearing loss (170). "Shotgun" approaches employing a battery of simultaneously administered treatments directed at common potential causes of sudden hearing loss are discouraged. The efficacy of antiviral agents, anticoagulants, vasodilators, rheologic agents, free radical scavengers, ginkgo products, and other drugs is unproved in patients with idiopathic sudden hearing loss (75; 33; 148; 170); most studies have been uncontrolled trials, and results are not clearly different than the natural history of this condition. Surgery is rarely indicated, except possibly in cases where clear evidence of perilymphatic fistula exists or to manage associated problems (eg, facial palsy in Ramsay Hunt syndrome).

Systemic corticosteroids, or a combination of systemic and intratympanic steroids, have been considered the “current standard treatment” and had been thought to be modestly effective in treating idiopathic sudden hearing loss (191; 122; 55; 41; 03; 110; 167; 32; 33; 148; 31; 137; 149; 169; 52; 135; 101; 176; 88). Steroids have also been used in patients with sudden hearing loss and known recent viral infections, autoimmune disease (eg, Crohn disease or ulcerative colitis), or meningitis (40; 11). Most of the reported benefit of steroids was within the first 1 to 2 weeks after onset, which is also the typical timeframe for spontaneous recovery, and little, if any, benefit could be expected if initiated four weeks or longer after onset (148). Unfortunately, available trials of corticosteroids for sudden hearing loss are generally of poor quality and have shown inconsistent and contradictory results (188; 35). Systematic syntheses and meta-analyses have failed to support the use of corticosteroids for sudden deafness and, instead, have concluded that “systemic or intratympanic steroid administration does not have a significant treatment effect” (188; 35; 67).

An international panel of experts at the IFOS 2017 ENT World Congress in Paris, France, reached a consensus that acknowledged the lack of evidence supporting steroid use, but nevertheless, the panel concluded that it was the current standard of care: “Although evidence of the efficacy of systemic steroids cannot be considered as strong enough to recommend their use, it is still the most widespread primary therapy and can be considered as the current standard of care” (109).

Some randomized trials found no difference in the rate of hearing improvement between systemic, intratympanic, and combined corticosteroid therapy for sudden hearing loss (09; 181). In a nonrandomized retrospective series of primary treatment of sudden hearing loss, in which the level of hearing loss is 70 to 89 dB HL, the addition of intratympanic steroids to the treatment significantly increased the success rate (38). In another nonrandomized retrospective case series there was no as no significant difference in hearing outcomes between the 4-injection (on days 1, 2, 4, and 7) and 2-injection (on days 1 and 2) groups receiving intratympanic steroids for the primary treatment of sudden hearing loss (179).

Some authorities recommend intratympanic dexamethasone only for subsequent or salvage treatment of idiopathic sudden sensorineural hearing loss (137; 48; 135; 88). Indeed, based on a systematic review of available studies, intratympanic corticosteroid therapy has been prescribed primarily when there is failure of conventional therapy and when systemic corticosteroids may aggravate comorbid illness, such as with diabetic patients (15). Steroids for salvage treatment of patients failing traditional therapy may have a beneficial treatment effect in a meta-analysis of available trials, although this is only a tentative conclusion because of the poor quality of component trials (35). If administered, intratympanic steroids should be administered within six weeks of onset of hearing loss and should be reserved for patients with at least severe sensorineural hearing loss (ie, pure-tone average greater than 50 dB and speech discrimination less than 50%) (110) or as “salvage therapy” for patients who do not improve with oral corticosteroids (02; 148; 31; 192). According to current clinical practice guidelines, intratympanic steroid perfusion should be offered in patients with incomplete recovery from idiopathic sudden sensorineural hearing loss after failure of initial management (170), and when used as salvage therapy, intratympanic steroids can result in significant gains in hearing (192).

Adding low molecular weight dextran to oral corticosteroids is not associated with greater hearing gain or better hearing outcome in patients with idiopathic sudden sensorineural hearing loss (185), although a benefit is claimed for dextran infusion in the peripartum period based on case series data (200). Before this treatment is considered, a well-designed randomized controlled trial showing clear benefit is needed.

In preliminary studies, topically applied recombinant human insulin-like growth factor 1 (IGF1) using gelatin hydrogels was associated with a significant improvement in pure-tone thresholds in patients considered refractory to systemic steroids (128; 127; 130). The major effects of this salvage therapy are thought to occur in the first four weeks after treatment.

Hyperbaric oxygen therapy (HBOT) is an option within three months of diagnosis of idiopathic sudden sensorineural hearing loss, though its effectiveness remains possible but unproven (04; 63; 170; 36; 164; 05; 28; 193; 22). A matched control retrospective case series demonstrated no significant difference in hearing outcomes between patients receiving salvage therapy with HBOT and intratympanic steroids compared to patients receiving intratympanic steroids alone (05). Another case series suggested that HBOT is a safe and beneficial adjuvant therapy for patients with idiopathic sudden sensorineural hearing loss (193). In contrast, a prospective randomized trial in 60 affected soldiers with idiopathic sudden sensorineural hearing loss found that hearing recovery on day 180 was significantly better in those who received the conventional treatment plus HBOT (28). A short delay to HBOT, more severe hearing loss at presentation, and younger age are the best predictive factors of improved hearing loss (164). However, these are exactly what would be expected as indications of greater spontaneous recovery. In a randomized trial of 171 patients with sudden sensorineural hearing loss randomly assigned to HBOT, oral steroids, or both, HBOT was the most efficacious treatment when started within seven days from sudden sensorineural hearing loss onset, while HBOT plus oral steroids were most efficacious when treatment was started more than 14 days from symptom onset (22). Outcome of HBOT is poor if treatment is delayed over 28 days (164). Further well-designed randomized controlled trials are needed to clarify the role of HBOTs.

Patients with identified etiologies for sudden sensorineural hearing loss may require targeted specific therapies. For example, patients with Ramsay Hunt syndrome should be treated with acyclovir (1 gm daily for 10 days), but available data do not suggest a benefit of antiviral agents in clinically diagnosed viral neurolabyrinthitis (174). Anecdotal evidence suggests that infliximab may be helpful in some cases of sudden deafness due to autoimmune inner ear disease (61). In addition, psychotherapy has been employed successfully in some patients with psychogenic sudden deafness (13).

N-acetyl-cysteine, which has been claimed to have antioxidant effects, has been reported to potentially be beneficial as a treatment for sudden hearing loss (24), but this needs to be confirmed with a well-designed double-blind, randomized controlled trial.

In diabetics, control of blood glucose level during treatment of sudden deafness does not have a direct effect on prognosis (120).

Associated vertigo and the concomitant nausea and vomiting should be treated symptomatically with medications; vestibular rehabilitation should be begun early (91). For those who do not recover from idiopathic sudden deafness in their only hearing ear (ie, producing bilateral deafness), cochlear implantation can be considered as early as three months after initiating treatment of sudden deafness (102). Cochlear implantation in unilateral sudden hearing loss with a normal functioning contralateral ear may also prove to be an effective therapy (18). Available data suggest that subjective tinnitus, speech discrimination, sound localization, and speech comprehension are improved by cochlear implantation in selected patients.

A multidisciplinary rehabilitation approach involving audiological may be necessary to help patients cope with the complex issues associated with sudden deafness (20). Personalized psychological interventions and pharmacological therapy may be helpful in management of anxiety and depression associated with sudden deafness (177).