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Intratympanic Therapy for Sudden Hearing Loss

SUJANA S. CHANDRASEKHAR

Sudden sensorineural hearing loss (SSNHL) is a rare otologic emergency. The incidence of SSNHL in the United States is 4000 cases annually (5-20:100,000).¹ Fifteen thousand cases are reported annually worldwide. This accounts for 1% of cases of sensorineural hearing loss (SNHL). The definition is 20 to 30 dB SNHL occurring in at least three contiguous frequencies over less than 3 days. Generally, the patient notices the hearing loss upon awakening. The average affected age is 40 to 50 years, but individuals of any age group can be affected. SSNHL can be bilateral in up to 2% of patients; when it is bilateral, patients tend to be older, have a higher incidence of vascular disease, and are more likely to have a positive antinuclear antibody titer.²

Frequently, the hearing loss is associated with other otologic symptoms such as tinnitus in 70% and vertigo in 50%. SSNHL is often described by audiometric configuration because there is some correlation between the shape of the initial audiogram and outcome.³ Shapes of the initial audiograms are downward-sloping (high frequency loss) in 39.7%; upward-sloping (low frequency loss) in 24.4%; flat in 15.3%; U-shaped (midfrequency loss) in 8.6%; and profound hearing loss in 11.9%.

The management of the patient with SSNHL is not straightforward. Dilemmas in therapy are due to several factors, including spontaneous remission rates, multi-factorial etiology, sporadic occurrence, and frequent delay in diagnosis or treatment. The natural history of the disease is that recovery rates without treatment range from 32 to 70%.^{4, 5} In addition, the recurrence rate with or without treatment is up to 28%. There appears to be a heterogeneous pathophysiology of SSNHL that includes viral insults, vascular compromise, some combination of those two entities, and possible inner ear membrane breaks. The infrequent occurrence of this problem makes it difficult for a single clinician to conduct valid studies of treatment effect. The patient may be undertreated or may face a delay in reaching the appropriate physician.

SSNHL is nonidiopathic in 10% of cases.¹ The possible causes attributed to SSNHL are myriad and are listed in Table 30 Up to 4% of patients with SSNHL will have an acoustic neuroma (vestibular schwannoma)(AN[VS]).⁶ Thirteen percent of patients with known AN (VS) had experienced SSNHL at some point in their course. The SSNHL in these cases may have recovered completely. Therefore, a retrocochlear evaluation is mandatory in the workup of patients with SSNHL. Of interest, hearing preservation rates after AN (VS) surgery are not affected by history of prior SSNHL with hearing recovery.⁷ Multiple sclerosis usually affects hearing as part of a constellation of brainstem findings; however, isolated cochlear loss has been reported.⁸ Hearing loss from autoimmune disease may result from immunologic reactions to inner ear proteins or as cochlear nerve neuritis (mono-or polyneuritis).^{9, 10}

Workup of the patient with SSNHL includes a complete neurotologic history and examination and audiogram at time of presentation and then at intervals during treatment or observation. Immitance audiometry and magnetic resonance imaging (MRI) scan of the internal auditory canals and cerebellopontine angles should not be overlooked, but may be delayed for a few weeks to minimize additional noise-induced hearing trauma during the acute phase of the SSNHL. MRI in SSNHL can be abnormal up to 35% of the time.11 Although diabetes and lipid abnormalities have been associated with hearing loss, the utility of extensive blood testing in patients with no suspicious history remains unproven. The tests most often done by otologists are erythrocyte sedimentation rate (ESR), Venereal Disease Research Laboratory (VDRL) test and fluorescent treponemal antibody absorption (FTA-ABS) test for syphilis, and serum for autoimmune inner ear disease (AIED) evaluation.¹²

Ninety percent of SSNHL is idiopathic (ISSNHL), and ISSNHL is most probably multifactorial in etiology. This may explain the high degree of variability in prognoses and treatment responses. The two common theories of etiology of ISSNHL are circulatory disturbance and inflammatory reaction.

The circulatory disturbance theory is based on four pathophysiological events in the inner ear: vascular occlusion, thrombosis, hemorrhage, and vascular spasm. Fisch et al studied perilymph oxygen tension and found it to be decreased by 30% in patients with ISSNHL.¹³ Ciuffeti et al performed blood filterability tests and showed disturbances in cochlear microcirculatory blood flow in SSNHL.¹⁴

Conversely, Schuknecht and Donovan examined 12 temporal bones of patients with SSNHL, and all of these showed normal vascular systems.¹⁵ Changes of the organ of Corti were likewise not characteristic of vascular occlusion. The difficulty of correctly interpreting the histopathologic findings is that patients generally do not die within a short time of their SSNHL, allowing time for vascular damage to recover, at least histologically.

The viral inflammatory reaction theory is supported by the following data.^16,17 Thirty-three percent of patients with ISSNHL report preceding viral upper respiratory symptoms. There is reported seroconversion of SNHL patients to the following viruses: influenza B, mumps, measles, rubella, cytomegalovirus (CMV), and varicella zoster. Viral inflammatory cochleitis is caused by mumps, rubella, CMV, and rubeola. The histopathology of ISSNHL contains many features that are consistent with viral infection, including hair cell loss, ganglion cell loss, strial atrophy, and inflammatory viral cochleitis.^14,18

The two theories of ISSNHL etiology are not mutually exclusive. Viral insult can cause direct neural injury, direct vascular structure injury, and direct injury to erythrocytes, leading to secondary microvascular insufficiency. Viruses can also lead to inflammation, which then causes vascular insufficiency.

Mattox and Simmons reviewed 166 patients with SSNHL in 1977.⁵ The overall spontaneous (nontreated) recovery rate was 65%. In their series, audiometric configuration was important, in that patients with upward-sloping audiograms (low frequency hearing loss) had better outcome; additionally, one third of patients with SSNHL had a preceding viral upper respiratory infection (URI). Treatment with IV hista-mine was not beneficial and resulted in poorer hearing thresholds. However, it must be kept in mind that this was neither a placebo-controlled nor a blinded study. Their conclusion was that SSNHL does not necessitate treatment. Several clinicians continue to hold to this dictum.

The majority of unilateral SSNHL patients experience hearing handicap and tinnitus handicap, 86% and 57%, respectively, in one questionnaire-based study.¹⁹ Thus a majority of senior otolaryngologists choose to treat these patients, although the method and combination vary widely.^{20, 21} Treatments advocated for SSNHL include steroids, niacin, histamine (sublingual, intravenous, or subcutaneous), lipoflavonoid vitamins, ProBanthine, diuretics, antibiotics, papaverine, systemic antiviral agents, carbogen, Cyclandylate, ginkgo biloba, and others.

Fetterman et al performed a retrospective review of treatment outcomes in a group of 837 patients with SSNHL.¹² Subjective improvement was found in 58%; audiologic improvement was seen in 52%. Seventeen percent of affected ears improved to a speech reception threshold of <30 dB. Of ears with initial profound SNHL, 46% improved with treatment. Clinical parameters most predictive of outcome included initial speech discrimination score (SDS), which was the most important parameter, initial pure-tone average (PTA), initial threshold at 4 kHz, younger age, and increased number of treatments. For all three hearing parameters, patients with worse initial hearing had better outcome, an unusual finding.

Wilkins et al offered a shotgun regimen of dextran, histamine, Hypaque, diuretics, steroids, vasodilators, and carbogen inhalation to 109 patients with ISSNHL.22 Of the patients who received the full protocol, 36% had complete or good recovery, with an average improvement of 19 dB PTA and 38% SDS. Of the patients who received only a partial protocol, 51% had complete or good recovery, with an average of 28 dB PTA and 50% SDS improvement. The reason for the better outcome with a partial treatment protocol appears to be that this study was not blinded or randomized, and patients with worse initial hearing tended to receive the full protocol.

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