Disclaimer: The information contained within the Grand Rounds Archive is intended for use by doctors and other health care professionals. These documents were prepared by resident physicians for presentation and discussion at a conference held at Baylor College of Medicine in Houston, Texas. No guarantees are made with respect to accuracy or timeliness of this material. This material should not be used as a basis for treatment decisions, and is not a substitute for professional consultation and/or peer-reviewed medical literature. Sudden Sensorineural Hearing Loss Sudden sensorineural hearing loss (SHL) is one of the most perplexing and controversial unsolved mysteries in otolaryngology. SHL has no universally accepted definition, but one useful definition is an idiopathic hearing loss of sensorineural origin, greater than 30 dB in three contiguous frequencies that occurs in less than three days. Most patients report onset of hearing loss within minutes to several hours. About one-third of patients will awaken with the loss; others may discover the problem when they try to use the telephone, or may describe a brief period of fluctuating hearing before the loss. About 50% of patients complain of concomitant unsteadiness or vertigo. Most studies find no seasonal, geographic, ethnic, racial or sexual predilection for SHL. The right and left ears appear equally vulnerable. In a series of 225 cases, Byl in 1984 noted bilateral SHL in 2% of patients. Reported overall incidence of SHL ranges from 5% to 20% per 100,000 persons per year. The mean overall age for SHL is 46 years, according to a large series by Mattox and Simmons. Sudden hearing loss is most likely a symptom rather than a discrete disease, merely representing the end result of many insults to the inner ear. Known etiologies of sudden hearing loss include multiple sclerosis, Cogan's syndrome, Buerger's disease, macroglobulinemia, leukemia, sickle cell disease, polycythemia, syphilis, bacterial infection, mumps, ototoxic drugs, metastatic tumors, trauma, and lupus. Ten percent of patients with Meniere's disease and up to 10% of acoustic neuroma patients will present with sudden hearing loss. In patients with sudden hearing loss, all of these known etiologies should be considered and ruled out before the most common "diagnosis" - idiopathic sudden hearing loss (SHL) - is accepted. Among patients with SHL, four etiologic theories remain pre-eminent: viral, vascular, membrane rupture, and auto-immune. Viruses have long been suspected as etiologic agents in SHL. Wilson et al, in 1983, studied 122 patients with SHL in the Boston area, and documented 63% viral seroconversion, compared with 40% of controls. Conversion rates were statistically significantly higher for mumps, rubeola, varicella-zoster, influenza, and CMV. Mumps virus was cultured from the perilymph of a patient with SHL by Westmore in 1979, and CMV has been cultured from the perilymph of a congenitally infected infant. Davis, Davis and Johnston, and Shimokata et al documented viral infection of the inner ear in animal models with CMV, mumps, and rubeola, respectively. However, SHL has not successfully been induced in an animal model using viruses. Schuknecht and Donovan in 1986 studied the temporal bone pathology in twelve ears with SHL and reviewed the literature for ten others; comparing the histopathologic findings in these SHL patients with findings from patients with known viral labyrinthitis, they found similar degenerative changes: atrophy of the organ of Corti, tectorial membrane, and stria vascularis in most cases. They concluded that viral cochleitis was the most probable cause of SHL. Simmons in 1968 proposed a double membrane break theory for SHL. Goodhill et al in 1973 discovered perilymph fistulas in three patients with sudden hearing loss, thus establishing round and oval window breaks as accepted etiologies for sudden hearing loss. Intracochlear membrane breaks, with and without round or oval window breaks, as a cause for SHL, have been poorly supported clinically and histopathologically. Most patients with SHL do not provide a history suggestive of implosive or explosive forces on the membranous labyrinth; Schuknecht and Donovan found no active or healed membrane breaks in the twelve temporal bones they examined. A vascular etiology for SHL is logically appealing, since sudden onset is suggestive of a vascular event. Sudden hearing loss has been observed in patients with vascular or coagulatory defects. However, histopathologic findings after permanent occlusion of the labyrinthine vasculature include necrosis of the membranous labyrinth followed by ossification and fibrosis - these findings are not consistent with those seen in most cases of SHL. Furthermore, temporary occlusion of the internal auditory artery was studied by Perlman et al in 1959, and these workers found irreversible loss of cochlear function after about one hour. They found that the hair cells, ganglion cells, and spiral limbus were the structures most frequently affected. These histopathologic findings are at odds with those from SHL ears studied. The irreversibility of the loss is also inconsistent with the reversibility of SHL in most cases. Finally, SHL typically strikes relatively young patients without systemic manifestation of vascular disease. This population seems unlikely to suffer isolated labyrinthine vascular compromise. In recent years autoimmune ear disease has been added to the theoretical etiologic triad of vascular, viral, and membrane rupture. Lehnhardt in 1958 first theorized that bilateral hearing disorders could result from autoimmune reactions directed against inner ear antigens. McCabe in 1979 first proposed the clinical entity of autoimmune sensorineural hearing loss. Yoo et al in 1983 induced autoimmune sensorineural hearing loss in rats by immunization with type II collagen, and demonstrated the presence of monoclonal antibody to type II collagen within the otic capsule. Harris in 1983 demonstrated the full competence of an independent inner ear immune system, capable of producing its own antibodies. In further work reported this year, Drs. Yamanobe and Harris isolated five autoantibodies to inner ear-specific antigens in patients with idiopathic sensorineural hearing loss. No study has yet detected inner ear-specific autoantibodies in SHL, and no study has proven the development of SHL in animal models using such antibodies. The role of autoimmunity in SHL has yet to be clarified. Given the lack of understanding of the etiology or etiologies of SHL, treatment regimens have of necessity been empirical. One of the most commonly used treatments is vasodilator therapy. Many agents have been tried, but one of the most popular has been carbogen, which is a gaseous mixture of 5% CO2 in 95% O2. Ugo Fisch in 1983 compared carbogen therapy with papaverine and low molecular weight dextran therapy in SHL patients. He found no significant short term difference in hearing results, but discovered significantly better hearing in carbogen-treated SHL patients after one year. Wilson et al in 1980 reported a double-blinded study of 67 SHL patients treated with steroids or placebo, and included an additional 52 controls who received no treatment. They found that patients with isolated midfrequency losses recovered without regard to therapy, and that 76% of patients with losses greater than 90 dB failed to recover regardless of therapy. However, in 74 patients with hearing loss less than 90 Db not limited to the midfrequencies, 78% treated with steroids improved, compared with 38% of untreated patients. Subsequent studies have confirmed the benefit of steroids in selected patients. This is the only controlled study showing conclusive superiority of any treatment for SHL over no treatment. Other treatment regimens have included diuretics, anticoagulants, plasma expanders, and diatrizoate meglumine, or Hypaque, an intravenous contrast dye. Controlled studies have not been performed to show a benefit from any of them. Stellate ganglion block is an invasive technique used in SHL therapy. Ganglion block causes vasodilation and subsequent increased blood flow through sympathetic blockade. Haug et al from Houston reported in 1976 that 70% of 56 patients with SHL treated by a series of blocks experienced greater than or equal to 10 dB pure tone average improvement and over 10% gain in speech discrimination scores, versus only 20% of 20 patients treated by other means. Because this procedure involves deep injection of anesthetic in the low neck, it carries obvious risk of lung injury and injury to vital neural and vascular structures. Many centers, including Baylor, use a so-called "shotgun" approach to SHL treatment, in an attempt to address all theoretical etiologies. Wilkins et al in 1987 evaluated one exhaustive shotgun regimen of dextran, histamine, Hypaque, diuretics, steroids, vasodilators, and carbogen, but found the results no different from those for no treatment. It is generally agreed that spontaneous recovery is common in SHL, usually occurring within two weeks of onset. Mattox and Simmons stated that 65% of all SHL patients will have spontaneous recovery of functional hearing without treatment. Others have estimated that about one-third have spontaneous return to normal hearing, and another one-third have return to functional hearing with a residual deficit. Obviously, the ideal treatment protocol would improve on these numbers. Only steroid treatment, as evaluated by Wilson et al, in 1980, has been proven superior to no treatment, and this success came only in patients with moderate loss across many frequencies. Byl in 1984 reported a prospective study of 225 SHL patients. He found the most important factors influencing recovery to be severity of initial loss, degree of vertigo, and time from onset to initial visit. All of these factors were inversely related to degree of recovery. Other facts identified by Byl and others include patient age, shape of initial audiogram, and ESR. Byl found that patients under 15 years of age and over 60 recovered less well than their counterparts within these two age limits. Most researchers agree that SHL patients with upsloping and midfrequency loss audiograms recover the best, while those with downsloping initial audiograms fare the worst. Elevated ESR has been shown to be a negative prognostic sign. Tinnitus, present in 70% to 85% of SHL patients, has no prognostic value. Sudden sensorineural hearing loss remains a poorly understood and maddening problem for the otolaryngologist. Prognostic predictors include audiogram shape, severity of loss, patient age, presence of vestibular symptoms, and duration of symptoms. Viral and autoimmune mechanisms are currently the best etiologic candidates, but the heterogeneity of patients and findings makes the discovery of a single pathologic pathway for all SHL unlikely. Case Presentation A fifty-two-year-old Latin American man presented to Ben Taub General Hospital with a twelve hour history of sudden hearing loss in the left ear. The patient had been watching television when he felt a pop in his left ear, followed by tinnitus and subjective hearing loss. He denied dizziness, vertigo, nausea, or vomiting, and gave no history of straining, trauma, or barotrauma. He also denied any history of ototoxic drugs or otologic surgery. Hearing was subjectively normal bilaterally prior to this episode. Past medical history was remarkable only for insulin-dependent diabetes mellitus, and social history was negative for drinking, smoking, and drug use. Physical examination was unremarkable except for tuning fork tests indicating a left sensorineural hearing loss. The patient had a negative fistula test and no spontaneous nystagmus. Laboratory studies were all within normal limits, including an ESR of 2 and negative syphilis serologies. Admission audiogram showed a pure tone average of 73 dB on the left and 8 dB on the right, and speech understanding depressed to 32% on the left, normal on the right. Tympanograms were Type A bilaterally. The patient was admitted and put to bedrest with a low salt diet. He underwent stellate ganglion blocks times three, and was started on a prednisone taper from 80 mg and given carbogen treatments. He experienced subjective improvement in his hearing on day three, and repeat audiogram on day four showed pure tone average of 42 on the left, with speech discrimination of 60%. The patient was discharged on day 5 on prednisone taper and low salt ADA diet, with light activity. Outpatient MRI of the head was normal. At follow-up two months later, the patient reported subjective return of normal hearing. Audiogram showed pure tone average of 12 dB on the left, 8 dB on the right, with 100% speech discrimination bilaterally. Bibliography Alford BR, Shaver EF, Rosenberg JJ, Guildford FR. 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Yoo TJ, Tomoda K, Stuart JM, Cremer MA, Townes AS, Kang AH. Type II collagen induced autoimmune sensorineural hearing loss and vestibular dysfunction in rats. Ann Otol Rhinol Laryngol 1983;92:267-271. Yoon TH, Paparella MM, Schachern PA, Alleva M. Histopathology of sudden hearing loss. Laryngoscope 1990;100:707-715. Grand Rounds Archive | Department Home page BCM Public | BCM Intranet | Privacy Notices | Contact BCM | BCM Site Map | ©2001-2006 Baylor College of Medicine
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