Portuguese Version

Year:  2004  Vol. 70   Ed. 2 - (14º)

Artigo de Revisão

Pages: 238 to 248

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Sudden deafness

Author(s): Roberto Alcantara Maia 1,
Samir Cahali 2

Keywords: Sudden deafness

Abstract:
Sudden deafness is characterized as a sensorineural deafness, having an abrupt onset and an unknown cause. It is usually unilateral; tinnitus is present in approximately 80 percent of all cases and vertigo in 30 percent. The differential diagnosis includes some others diseases, such as infectious, hematological, neurological and most likely, the vestibular schawnnoma. The etiophatogenic factors of sudden deafness are unknown; some hypothesis are considered: experimental studies have proved the vascular hypothesis, which is well known; the viral hypothesis is widely accepted, but it has failed in the laboratorial comprovation; most recently the appearance of the autoimmune hypothesis which was proved by immune laboratorial studies, and finally, the hypothesis of the membrane's rupture (fistula's theory) is behind the others because of the difficulty in proving it. Sudden deafness is ultimately considered as an entity of multifactorial ethiopathogenic factors. Treatment of sudden deafness is very controversial. The administration of corticosteriods and vasodilatators drugs is widely accepted since prescription is easily done and inexpensive. The correct approach to sudden deafness is to individualize each patient and to establish different types of treatments depending on the needs of each case. In the near future, different kinds of treatment will take the place of the famous protocols treatments encouraged by many authors.

INTRODUCTION

Sudden deafness is a sudden loss of hearing of sensorineural nature normally unilateral that does not present a well defined etiological factor, that is, it is still of unknown cause. SIMMONS (1973), one of the main scholars in the area, wisely conceptualized sudden deafness as follows: "sudden deafness is a symptom in search for a diagnosis". It is considered a case of medical emergency and should be promptly diagnosed and treated.

The first description and publication of a group of patients that had "sensorineural deafness of sudden onset and idiopathic origin" was made by DE KLEYN in 1944. The author believed that the cause of sudden deafness was related to the brainstem, caused by some kind of unknown vitamin deficiency. Its publication was the first and dictated the pattern for further studies to come. In all the studies there was report of cases affected by sudden deafness and submitted to different types of treatment (MATTOX, SIMMONS, 1977).

Sudden deafness is one of the most controversial topics in Otorhinolaryngology, reason for heated discussions among authors that dedicate to the topic. Practically all its issues are controversial, since they are not well known nor defined. Since the real mechanisms of sudden deafness are still unknown, the dispute starts from definition and continues up to management.

The main controversial issue always present in discussions on sudden deafness is how to treat the affected patients. The world medical literature reports quite many different therapeutic approaches to treat the disease. Between the two extreme treatment approaches, we can find different regimens and protocols. One of the extremes proposed by some authors is to do nothing in cases of sudden deafness, that is, no treatment (GUYOT, THIELEN, 2000). The other extreme proposed by different authors advocates the conduction of surgery (SIMMONS, 1968).

The controversial debate concerning the optimal treatment approach is a result of a series of factors. Since it has low population prevalence, the studies about the topic present few patients in the samples. Since it also includes different aspects concerning incidence and forms of affection, there are a number of variables to be taken into account. Therefore, the groups of studied patients are limited in number and very heterogeneous, which makes it very difficult to compare results of different treatment approaches used by different authors in the area.

LITERATURE REVIEW

I - Definition and diagnosis

DEBAIN (1957) was one of the first authors to define sudden deafness. He considered it "inner ear deafness, severe or total, whose onset is sudden or very quick, in a situation of apparent calmness, with no accompanying signals, no evident cause and no tendency to spontaneous regression".

The diagnostic criteria that are more accepted and precise were defined by the Committee on Sudden Deafness Studies, Health Department of Japan, in 1973 (NOMURA, 1988). The diagnosis includes minor and major criteria.

The major criteria are:

 sudden loss of hearing;
 uncertainty about cause of deafness;
 hearing loss that is normally severe, non-fluctuating and unilateral, most of the times.

The minor criteria are:

 tinnitus, which can be absent;
 dizziness, which can also be absent;
 absence of neurological signs, except for involvement of the 8th cranial nerve.

The diagnosis of sudden deafness is considered absolutely certain when all minor and major criteria are met; the diagnosis is considered probable when only two out of the major criteria are met.

II - Epidemiology

Sudden deafness is considered an affection of relatively low incidence. According to SIMMONS (1973) its incidence is probably underestimated, since many patients with sudden deafness recover spontaneously and the cases never come to physicians' knowledge. Other patients, in case of symptoms' persistence, would first look for a general practitioner, would not undergo audiological tests, and would be treated with decongestants, being that in the absence of improvement, they would be referred to specialized service and properly diagnosed. BYL (1984) conducted surveys and reported an incidence of 5 out of 20 cases, with an average of 10.7 cases per 100,000 subjects per year.

The affections of sudden deafness are normally unilateral. FETTERMAN et al (1996) conducted a retrospective ten-year study and presented 823 cases of patients, with an incidence of 1.7% of bilateral cases.

The incidence by gender is similar in male and female subjects. FETTERMAN et al (1996) in their studies of 823 patients presented 53.4% men and 46.6% women. FORMIGONI et al (1998) conducted a study of 48 cases in Brazil and found 58% men and 42% women.

The age of affected patients is very wide. According to MOSNIER et al (1997) most of the patients are aged between 40 and 60 years. FETTERMAN et al (1996) in their studies of 823 patients showed an average age of 52.3 years, with standard deviation of 16.1 years. FORMIGONI et al (1998) in their study with 48 cases, reported an average age of 43.3 years, with patients aged 15 to 72 years.

The most frequent symptoms are tinnitus and dizziness. Tinnitus were present in 70% to 90% of the cases (BYL,1984). FETTERMAN et al (1996) in their study reported an incidence of tinnitus of 91%. FORMIGONI et al (1998), in 48 cases, found an incidence of tinnitus of 94%. Dizziness was present in 20% to 40% of the cases (BYL,1984). FETTERMAN et al (1996) found an incidence of 43% of vestibular symptom and FORMIGONI et al (1998) found an incidence of 50% of vertigo.

III - Differential diagnosis

In the attempt to identify the etiological diagnosis, many factors and causes have been described and related to sudden deafness.

III/A -Infectious diseases

KATHOLM et al (1991) described a case of an 18-year-old female subject that presented sudden deafness on the right ear and three months later, she had sudden deafness on the left ear. In both ears, she had total hearing loss. In the diagnostic and etiological investigation, the authors concluded that it was a case of acute toxoplasmosis. Even though she was treated with drugs, she never recovered her hearing. The authors emphasized the importance of investigating toxoplasmosis in cases of bilateral sudden deafness.

The correlation between sudden deafness and Lyme's disease was studied by PELTOMAA et al (2000), who investigated the prevalence of positive response to antibodies Borrelia burgdorferi in 165 patients with sudden deafness in Finland. The authors demonstrated that the antibody level was on average six times higher in the 165 cases of deafness than in the general population of the country. Four patients met all the criteria for Lyme's disease. They suggested that in endemic areas a search for Lyme's disease should be conducted in all cases of sudden deafness, since this sudden loss of hearing has a specific treatment approach.

Acquired immunodeficiency syndrome (AIDS) has been related with sudden deafness by some authors. In Brazil, two studies reported it: BOHADANA et al (1998), who presented a 33-year-old male patient with sudden deafness and positive HIV without any other manifestation of AIDS, and CARVALHO et al (2001) who presented a 41-year-old male patient with asymptomatic HIV for 4 years that developed sudden deafness.

III/B -Hematological diseases

RESENDE et al (2000) conducted a survey in 16 publications with 27 descriptions of clinical cases of chronic myeloid leukemia associated with sudden hearing loss. The authors presented a case study of a patient with hyperleukocytosis owing to chronic myeloid leukemia and bilateral sudden deafness. Three patients with aplastic anemia that developed unilateral sudden deafness were described by OHINATA et al (1994). These patients manifested, in addition to erythrocytopenia, thrombocytopenia that, according to some authors, would probably trigger intracochlear hemorrhage.

III/C -Neurological and neurovascular diseases

Sudden deafness has been described as an initial symptom in patients with multiple sclerosis. DRULOVIC et al (1994) reported two cases. The authors came to the diagnosis of multiple sclerosis by the association with the results of auditory brainstem audiometry and magnetic resonance imaging. They emphasized the importance of these exams in the diagnosis of sudden deafness.

There are a number of reports of affections in the region of vertebral and basilar artery in patients with sudden deafness. SCHMIZ et al (2000) reported a case of a patient that was initially diagnosed as having idiopathic sudden deafness, without any other neurological sign in the initial stage. Owing to the presence of severe labyrinthic symptoms, he was submitted to angioresonance that demonstrated basilar artery thrombosis. This patient was submitted to early anti-coagulant treatment with heparin, presenting gradual improvement of the condition. ARAI, ISHIDA (2000) described the case of a patient with bilateral sudden deafness associated with vertigo, with no cerebellar or brainstem signs. Reassessed with angio-MRI, the radiologist detected occlusion of right vertebral artery.

III/D -Vestibular Schwannoma

The association of vestibular schwannoma and sudden deafness is widely studied and reported in the medical literature.

OGAWA et al (1991) reviewed 132 patients with surgically confirmed vestibular schwannoma and they reported 29 patients (22%) who had history of sudden deafness. YANAGIHARA, ASAI (1993) described a series of 111 patients operated of vestibular schwannoma in which 21 patients (18.9%) had sudden deafness. In the 21 tumors found, nine were considered small, five were medium-sized and seven were large tumors. A total of 284 patients with vestibular schwannoma were described by MOFFAT et al (1994). Out of the total, 34 patients (12%) presented clinical picture of sudden deafness. The authors commented that the average duration of symptoms in these patients was 8 months, being shorter than in patients without sudden deafness. They did not observe significant difference in the groups with vestibular schwannoma with and without sudden deafness concerning size of tumor.

Magnetic resonance imaging has taken on the significant role of assessing patients with sudden deafness. WEBER et al (1997) assessed 16 patients with sudden deafness through MRI with gadolinium as contrast. Three patients presented relevant affections in the test. One of the three patients whose previous clinical treatment led to total recovery of hearing, demonstrated the presence of a 0.5cm vestibular schwannoma through MRI. The authors concluded that it is essential that a MRI with gadolinium be performed in all patients with sudden deafness of idiopathic origin. This assessment should be conducted some time during the clinical treatment, regardless of the obtained results. The use of MRI for the diagnosis of sudden deafness was studied in Brazil by BITTAR et al (1999) when they submitted 20 patients with diagnosis of sudden deafness to the test. In five patients (25%), there were significant findings in the MRI. In one out of 5 patients there was the presence of vestibular schwannoma. The authors concluded that MRI with gadolinium contrast should be performed in all patients with sudden deafness.

IV - Etiopathogenesis

Even though it is one of the most studied and analyzed topics, etiopathogenesis of sudden deafness is still controversial and undefined. Vascular and viral principles are the two most frequently reported hypotheses. Autoimmune disease and labyrinthic membrane rupture are hypotheses that have also been widely studied.

IV/A -Vascular hypothesis

PERLMAN et al (1959) were among the first authors to show the sensitivity of the cochlea to anoxia. They conducted experiments in which they occluded the labyrinthic artery and observed that: a 60-second occlusion was enough to cause a decrease in cochlear potentials, which were completely recovered once the occlusion was below 8 minutes, but the potentials were completely vanished if the occlusion time was greater than 60 minutes.

Vascularization of the inner ear is of terminal type. Any obstruction of blood flow, be it complete or partial, has immediate repercussion on the oxidative mechanism of the inner ear. The obstruction will lead to hypoxia or cell anoxia that leads to reduced production of ATP (adenosine-triphosphate), intracellular acidosis and accumulation of free radicals. These three processes change the cell enzyme mechanism leading to necrosis and cell death (MOSNIER et al, 1997).

One of the vascular pathophysiological mechanisms frequently described is increase in blood viscosity. Hyperviscosity causes reduction in capillary blood flow that ends up reducing oxygen transportation leading to tissue hypoxia. Studies of blood and plasma viscosity conducted in groups of patients with sudden deafness compared to the viscosity of normal control groups demonstrated significantly higher values for those subjects with sudden deafness (OHINATA et al, 1994).

Another vascular pathophysiological mechanism related with sudden deafness is the occurrence of thrombosis and embolism that cause cochlear ischemia. The migration of emboli to the labyrinthic artery was discussed and commented by PLASSE et al (1981) upon the report of seven cases of unilateral sudden deafness that occurred after the conduction of open heart surgery. Many studies have suggested the existence of cochlear vascular spasms, both isolated or associated with other vascular events to justify the origin of sudden deafness in some patients. This theory would also justify auditory recovery, which many patients experience as a result of the reversion of the probable vascular spasm that had occurred. COX et al (1997) advocated the hypothesis of vascular spasms to justify the occurrence of sudden deafness in three patients followed up by them and in other 20 patients described in the world literature. In all these patients, sudden deafness had occurred immediately after the conduction of non-otological or non-cardiovascular surgeries under general anesthesia.

The conduction of neurovascular diagnostic procedures in patients with sudden deafness was recommended by GUIRAL et al (1997). The tests normally conducted are transcranial color Eco Doppler to measure the blood flow in the territory of the labyrinthic artery and Angio-MRI. They stated that even though the diagnostic methods are very sophisticated, they are not very invasive. In a series of 13 patients with sudden deafness submitted to these tests, they found affections in 4 patients who had significant impairment of vertebral-basilar artery flow and they also showed stenosis or block of the labyrinthic artery.

IV/B -Viral hypothesis

The hypothesis of a viral process as the triggering element of sudden deafness is well accepted and discussed in the world literature. Chickenpox, rubella and herpes viruses are well known as causes of sudden deafness and sensorineural loss of sudden onset. The idea that subclinical forms of viral infections are the origin of sudden deafness is quite tempting (MOSNIER et al, 1997).

VAN DISHOECK, BIERMAN (1957) reported that one third to one fourth of the patients that present sudden deafness were affected by upper airways infections in the month before sudden deafness occurred. Conversely, other studies tried to demonstrate that the incidence of symptoms of upper airways before sudden deafness is similar when compared to groups of patients of sudden deafness in the general population (SIMMONS, 1973).

Viral serology studies in populations of patients with sudden deafness have demonstrated very contradicting results concerning the possibility of viral impairment of these patients. The correlation between sudden deafness and asymptomatic chicken pox was studied by OKAMOTO et al (1994). These authors also conducted studies with IgM antibodies that signaled a recent infection by chickenpox in 130 patients with sudden deafness. They were positive in nine patients (6.9%). They concluded that the asymptomatic infection by chickenpox seemed to be directly related with some cases of sudden deafness. YOSHIDA et al (1996) studied a group of 33 patients with sudden deafness and another control group of 11 normal subjects submitted to serology for titration of the following infectious agents: chicken pox, adenovirus, rubella, measles, herpes simples, varicella zoster; rhinosyncytial; cytomegalovirus and mycoplasma pneumoniae. They concluded that titration did not present any significant difference between the control group and those with sudden deafness.

PITKARANTA, JULKUNEN (1998) conducted a study with 20 patients with sudden deafness and 12 control subjects. In the two groups they measured the levels of existing proteins in leukocytes, named MXA, which is considered an efficient marker of systemic viral infections. They demonstrated there were no significant differences between the levels of this protein in the compared groups. They concluded that "the findings suggested that sudden deafness was not habitually associated with systemic viral infection".

IV/C - Autoimmune hypothesis

In recent years, there has been new evidence that autoimmune impairment of the inner ear could account for some cases of sudden deafness.

In order to determine the possible participation of autoimmune factors in sudden deafness, GARCIA-BERROCAL et al (1997) assessed a group of 22 subjects with sudden deafness and a control group of 14 normal subjects. They applied tests to identify the subpopulations of lymphocytes in the peripheral blood of patients with sudden deafness, before and after treatment with corticoids. They observed the occurrence of significant reduction of the number of lymphocytes CD4+ and CD8+ in the group with sudden deafness. These patients were then submitted to treatment with corticoids. In cases in which there was good hearing recovery, they observed tendency to normalization of lymphocytes; in cases in which there was poor auditory recovery, there was no trend of lymphocyte normalization. The authors concluded that "such abnormalities in the subpopulation of lymphocytes in patients with sudden deafness suggested the existence of autoimmune processes in the inner ear as a possible etiopathogenic factor of the affection".

In order to test the activation of sudden deafness complement, NORDANG et al (1998) analyzed 25 patients with sudden deafness. The results demonstrated significantly increased levels of component C3 of complement in relation to the control group. The authors concluded that the high levels of complement component C3 in these patients with sudden deafness indicated an activation of the initial portion of the complement cascade, which would imply the existence of inflammatory factors in these patients. The authors recommended the routine investigation of component C3 complement in patients with sudden deafness in order to identify which patients would be more benefited from antiinflammatory drug use.

HELLER et al (1998) conducted immunoserology tests in 55 patients with sudden deafness. Phospholipid antibodies were demonstrated in 49% of the patients. Serotoninic and gangliosidic antibodies were found in 53% of the patients. The authors commented that these three antibodies are habitually found in patients with fibromyalgia and chronic fatigue. They recommended that the patients with sudden deafness be questioned about symptoms related to these diseases. If symptoms are present, antibody test for phospholipids, serotonin and gangliosides should be ordered, since inner ear impairment can be related to autoimmune syndromes of fibromyalgia and chronic fatigue.

IV/C -Membrane rupture hypothesis

The hypothesis of rupture of the membranes of the inner ear was advocated and demonstrated by different authors to justify the etiopathogenesis of many cases of sudden deafness.

SIMMONS (1968 and 1979) proposed a theory of double rupture of the membranous labyrinth membranes. The author suggested that the rupture of the labyrinthic window would cause sudden loss of perilymph through the inner ear to the middle ear causing major decompensation of pressure between endolymph and perilymph compartments, leading to rupture of Reissner's membrane. The second rupture would cause a mix of perilymph and endolymph, considerably hindering cochlear physiology, which would cause a picture of hearing loss. The healing of these membranes, if present, would lead to stabilization of cochlear structures, with consequent auditory recovery.

Right after the description by SIMMONS (1968), many reports of patients with sudden deafness and perilymphatic fistula were published in the medical literature with descriptions of patients with sudden deafness and barotrauma. GUSSEN (1981) reported the case of a patient with unilateral sudden deafness after a plane trip; years later, when the patient died, it was possible to study her temporal bone and demonstrate the rupture of Reissner's membrane.

V- Prognostic factors

Different factors are analyzed in the literature as parameters for the prognosis of sudden deafness recovery. The main prognostic factors were studied by SIMMONS (1973) in a retrospective study of 89 patients. These authors observed a series of parameters that served as the basis to define the prognosis of final auditory recovery in a patient with sudden deafness:

1. Time from the onset of sudden deafness and the definition of the diagnosis (beginning of treatment) - in all cases good auditory recovery, diagnosis and treatment was defined in the first 14 days;

2. Type of pure tone audiometry curve - hearing loss in low frequencies recovered better than high frequencies hearing losses;

3. Severity of initial deafness - considering the auditory thresholds in pure tone audiometry, the mean of frequencies 500, 1000 and 2000 Hz, it is observed that the higher the initial thresholds the worse the auditory recovery;

4. Erythrocyte sedimentation rate - patients that presented high rates had worse auditory recovery;

5. Presence of severe dizziness - this symptom was related to worse auditory recovery;

6. Vestibular test showing vestibular loss in caloric tests - they are also associated with worse auditory recovery.

FORMIGONI et al (1994), in Brazil, conducted a study with 150 patients with sudden deafness whose purpose was to assess the predictive factors of final auditory prognosis. They concluded that the factors of good prognosis were: early treatment (up to 10 days) and age below 40 years. The poor prognosis factors were: severe hearing loss in the baseline assessment (greater than 45 dB) and presence of vertigo associated with deafness. They also stated that the type of audiometry curve in the baseline did not show correlation with the final auditory result.

Otoacoustic emissions were more recently applied as a prognostic tests for recovery of sudden deafness. SAKASHITA et al (1991) asked sudden deafness patients to undergo otoacoustic emissions tests at the baseline. The authors reported that even though the threshold of the mean of frequencies 500, 1000, 2000 and 4000 Hz of the patients with sudden deafness was greater than 35dB, otoacoustic emissions were not detected in half of the patients. In cases of sudden deafness with otoacoustic emissions present, the final auditory result was significantly better than in other patients, regardless of the severity of the baseline hearing loss.

VI- Treatment

There are a number of treatment propositions for sudden deafness in the world medical literature.

The controversy arises from the validity of treatment. Some authors are categorical to state that there is no evidence of any type of treatment for sudden deafness that causes better results than these obtained from the natural progression of the condition (BYL, 1984).

GUYOT, THIELEN (2000) analyzed 59 patients with sudden deafness in the period between 1983 and 1997. The patients deliberately refused to be submitted to the proposed treatment. The authors commented that the final audiological results of the 59 patients were similar to those obtained by different forms of treatment. The authors concluded that sudden deafness did not require treatment.

LOUHRAN (2000) sent a questionnaire to 100 Otorhinolaryngologists in different regions of England. The questionnaire asked about the management of patients with sudden deafness. The author received 76 responses. Most of the studied ENT physicians (89%) answered that they treated their patients with sudden deafness even though there was great variability of treatment approaches described by the physicians.

VI/A- Corticoids

WILSON et al (1980) described a double blind study in which 33 patients with sudden deafness were treated only with oral corticoids, whereas 34 patients with sudden deafness were treated with placebo as the only form of treatment. Post-treatment audiometric controls were conducted at week 4 and three months after beginning of treatment. The authors concluded that the groups of patients treated with corticoids had better statistically significant results than the group of placebo in moderate hearing loss. In sudden deafness with severe hearing loss, there was no statistically significant difference in recovery of hearing in both studied groups.

Corticoids are probably the most widely used drugs, either isolated or associated with other forms of therapy for the treatment of sudden deafness. The wide range of corticoids used is based on the antiinflammatory properties of these drugs. There is, therefore, a rationale for the use of this drug if based on the viral or autoimmune etiopathogenic hypotheses (MOSNIER et al, 1997).

VI/B- Vasodilators

Carbogen, which consists of a mixture of 95% oxygen and 5% carbonic gas has been advocated as the treatment for sudden deafness in many different studies. NAGAHARA et al (1983) demonstrated in an experimental model significant increase in partial pressure of oxygen in the perilymph during the inhalation of carbogen. According to these authors, carbogen has a marked vasodilating effect in cochlear circulation by direct action and through the sympathetic system. FISCH (1983) advocated the treatment of sudden deafness with carbogen inhalation and demonstrated superior results with this type of treatment when compared to other therapeutic regimens that use other vasodilators.

Another survey with vasodilators used in treating sudden deafness cases was conducted by MOSNIER et al (1997). These authors initially reported carbogen as a powerful cochlear vasodilator. Next, MOSNIER et al (1997) referred to two groups of vasodilators that were considered relevant in cases of sudden deafness. The first group was formed by drugs that had alpha-blocking action, named neurotrophic, with action over the sympathetic fibers. These drugs would act over the blood vessels with spasm, promoting dilation and favoring blood flow in the ischemic region. The second group of vasodilating drugs pointed out by the authors were calcium antagonists. These drugs prevent vasoconstriction caused by vasoactive substances to promote stabilization of vascular cell membranes.

VI/C- Dextran 40

Dextran 40 is a macromolecule whose action in microcirculation promotes an increment in blood flow to reduce pilling up of red blood cells in blood capillary system.

POSER et al (1992) described a group of 80 patients with sudden deafness treated for 10 days with daily infusions of Dextran 40, associated with vasodilator Naftidrofuryl. The authors reported significant improvement in hearing levels with this treatment regimen.

FORMIGONI et al (1998), in Brazil, presented a group of 48 patients with sudden deafness treated with daily infusions of Dextran 4- and nicotinic acid + papaverin + vitamin A. The authors reported that 60.41% of the patients submitted to this therapeutic regimen presented relevant audiometric improvement at the end of treatment.

VI/D- Normovolemic hemodilution

Normovolemic hemodilution in the treatment for sudden deafness that has been designed and advocated by DAUMAN et al (1983). The authors described the technique as follows: patient is lying down under heart monitoring, approximately 10% of total blood volume is removed through a peripheral vein of the arm; simultaneously, a perfusion of the same volume of Dextran is made on the other arm. The authors referred that after hemodilution hematocrit was between 30 to 35%. As a result of hematocrit decrease, there is reduced blood viscosity and, as a consequence, increase in blood flow, especially in the brain region. The final result is increment in blood oxygenation. DAUMAN et al (1983) conducted a comparative study of different forms of treatment in 36 patients with sudden deafness. The authors concluded that normovolemic hemodilution had results similar to other forms of treatment and should be highlighted since it is a quick, simple and apparently free from complication method.

VI/E- Hyperbaric oxygen therapy

Hyperbaric oxygen therapy is also used in the treatment of sudden deafness. It promotes increase in level of blood oxygen. Even though there is low blood flow, there is further supply of oxygen to the tissues, including at cochlear level.

MURAKAWA et al (2000) conducted a 10-year survey with 522 patients with sudden deafness treated with hyperbaric oxygenation. Oxygen was administered at 2.5 atmosphere pressure during 80 minutes a day, in 10 to 15-minute sessions. The authors reported that 161 patients, out of 522, were referred from other centers after initial attempt of treatment failed. The results obtained showed that 19.7% of the cases had complete recovery; 34.9% had partial improvement; 45.4% did not reach satisfactory results. The authors referred that 40% of the patients had already been treated with other regimens but with no significant results and presented improvement with hyperbaric oxygen therapy. The authors concluded that this therapy should be ideally conducted within the first 14 days since onset of sudden deafness. Another conclusion of the authors was that even when patients had not responded satisfactorily to previous treatment approaches, hyperbaric oxygen therapy had provided relevant benefits to an impressive number of cases.

VI/F- Amidotrizoate

MORIMITSU, USHISAKO (1988) described treatment of sudden deafness with intravenous use of amidotrizoate (Hypaque ), a drug used as angiographic contrast. The authors started to study in 1973 when they were conducting a vertebral angiogram in a patient with sudden deafness and observed auditory recovery after use of amidotrizoate. From then on, 47 patients with sudden deafness were treated exclusively with the drug. The medication was administered at 20ml intravenous doses in daily applications, for a variable period of days, up to stabilization of the hearing recovery process. The authors described complete recovery in 43% of the cases, partial recovery in 21% and no recovery in 36% of the cases.

VI/G- Ginkgo biloba

HOFFMANN et al (1994) described a group of 80 patients with sudden deafness treated with Ginkgo biloba EGB 761 extract, a vasoregulating drug that promotes increment of blood flow. The purpose of the study was to compare the auditory results of a group of patients treated with Ginkgo biloba with another one treated with naftidrofuryl, a vasodilating drug. The statistical analysis of audiometric recovery with the two methods showed similar results in both forms of treatment proposed. The authors commented that they did not detect any form of side effect in the patients treated with Ginkgo biloba, whereas in the group with naftidrofuryl there were some side effects resulting from drug use. In view of the results, the authors recommended treatment of sudden deafness with Ginkgo biloba EGB 761.

VI/H- Pentoxiphylline

LEUNIG et al (1995) presented a retrospective study with 118 patients with sudden deafness treated with venous infusions of hydroxyethyl associated with pentoxiphylline. The authors commented that hydroxyethyl is an alternative drug to Dextran, which in association with pentoxiphylline promotes a rheological synergic action, leading to increment in microvascular perfusion. The authors reported that in 118 patients treated with this therapeutic regimen, auditory improvement was reached in 75% of the cases.

VI/I- H.E.L.P. Therapy

WALCH et al (1996) presented a new form of sudden deafness therapy under the acronym H.E.L.P. (Heparin-Induced Extracorporeal LDL Precipitation). HELP therapy is a system through which extracorporeal circulation selectively eliminates plasma fibrinogen, LDL (low-density lipoprotein); cholesterol; triglycerides; lipoproteins. The result of this plasma filtering is reduction of the described macromolecules, leading to reduction of plasma viscosity and increment of blood flow in microcirculation. The authors reported that this form of therapy was used in patients with sudden deafness that after two weeks of treatment with vasodilators and corticoids had not presented auditory improvement. This protocol of treatment was applied in 5 patients that after therapy with HELP presented evident improvement of hearing, as reported by the authors.

C - DISCUSSION

Otorhinolaryngologists have known and studied sudden deafness for a long time. Despite the fact that the first reports were made by DE KLEYN in 1944, the controversies and main questions are still latent to present. Etiopathogenesis and treatment of sudden deafness are still probably the main questions to be answered.

A - Etiopathogenesis

The many studies about the probable etiopathogenesis of sudden deafness point towards different directions. The literature shows that there are four most widely accepted and debated etiopathogenic hypotheses.

The vascular impairment of the inner ear is normally considered with special emphasizes. Since the first studies by PERLMAN et al in 1959, who caused labyrinthic occlusion and observed the reflex of cochlear potentials, to the most recent studies by GUIRAL et al in 1997, using angio-MRI in patients with sudden deafness and vascular affections, in many of the patients it became evident the participation of vascular phenomenon in sudden deafness.

The etiopathogenic hypothesis of viral impairment of the inner ear also counts on many reports and studies in the literature. The correlation between chickenpox virus and sudden deafness, known by Otorhinolaryngologists, was studied and demonstrated in some patients by OKAMOTO et al in 1994. However, the main setback of the viral origin hypothesis is the impossibility to confirm the presence of significant viral plasma titration in populations of patients with sudden deafness when compared to the normal control populations (YOSHIDA et al, 1996; PITKARANTA, JULKUNEN, 1998).

The etiopathogenic hypothesis of rupture of membranous membrane, also known as the fistula theory, has been widely accepted in the world after the studies by SIMMONS in 1968. In past years, few studies suggested this hypothesis, which is no longer so widely accepted.

The etiopathogenic hypothesis most widely discussed in the literature in recent years is the autoimmune one. Autoimmune impairment of the inner ear has been known for many years now. As a result of the development of more sensitive diagnostic tools, many authors have demonstrated significant affections in patients with sudden deafness. The results demonstrate significant changes in the population with sudden deafness when compared to the normal control population. These authors are careful in their conclusions, but they always finish by suggesting the existence of autoimmune processes in the inner ear of patients with sudden deafness (NORDANG et al, 1998; HELLER et al, 1998).

The conclusion we can reach by studying the many different etiopathogenic hypotheses for sudden deafness is that it is certainly a multifactorial affection. The multiplicity of etiopathogenic mechanisms should be involved. For each case of sudden deafness, a specific etiopathogenesis is present, being that its confirmation will keep on being hardly achieved.

B - Treatment

Since etiopathogenic mechanisms of sudden deafness are so variedly and differently involved in each case, which would be the ideal treatment approach for sudden deafness patients? The controversial issues and the multiple treatment approaches present in the literature are evident confirmation of the doubts in the area. According to MOSNIER et al in 1997, most of the treatment approaches described have been directed against two of the main etiopathogenic factors: viral hypothesis and vascular hypothesis.

The wait and see management approach of sudden deafness proposed by GUYOT et al in 2000, after the observation of the final audiological diagnosis of treated patients was the same as those that refused treatment, find resistance from most Otorhinolaryngologists. These physicians probably feel uncomfortable simply not to treat a severe affection which is frequently irreversible. This situations was very well described by LOUHRAN in 2000, upon receiving affirmative responses that 89% of the physicians that had answered the questionnaire treated sudden deafness.

Corticoids, well presented by the studies of MOSNIER et al in 1997, are the most widely used drugs either isolated or associated with other forms of therapy. Its easy handling by Otorhinolaryngologists, associated with low cost and possibility of home care, makes it a simple and practical prescription. They will certainly keep on being the most advocated drugs for the treatment of sudden deafness.

Vasodilating drugs and therapies, many times associated with corticoids, are frequently referred in the literature. The use of carbogen, advocated by FISCH in 1983, found world acceptance after the study by NAGAHARA et al in 1983, which experimentally demonstrated the high impact of vasodilation in cochlear circulation. Different vasodilating drugs are referred by different authors in a great variety of studies. Similarly to corticoids, vasodilators are easy-to-use drugs and they are widely accepted in clinical practice. The rationale for vasodilating treatment is based not only on the vascular etiopathogenic hypothesis, but also on any other inner ear impairment by sudden deafness; once you improve blood flow in the cochlea, it is intended to have better metabolic conditions and regeneration capability.

The use of Dextran 40 in the treatment of sudden deafness is quite well known and used by different authors (FORMIGONI et al, 1998; POSER et al, 1992). The action mechanism of Dextran 40 is responsible for the increment in blood perfusion of cochlear microcirculation, improving tissue perfusion. This action would lead to benefits similar to the vasodilating therapies for the inner ear.

Normovolemic hemodilution in the treatment of sudden deafness was idealized and initially described by DAUMAN et al in 1983. The hemodynamic mechanism of this type of therapy is easy to understand and applicable in sudden deafness. The patient is submitted to monitored bleeding and thanks to simultaneous infusion of Dextran 40, the patient restores normal volemic volumes. Therefore, there is immediate and expressive reduction of hematocrit levels. With low hematocrit levels, blood viscosity decreases and, consequently, there is increase of blood flow in general. The greater blood flow in the cochlear microcirculation leads to improved perfusion and oxygenation of the cochlea. The results described by DAUMAN et al in 1983 were very promising. Based on these results, normovolemic dilution started to be used, especially in association with other treatments.

Hyperbaric oxygen therapy as treatment of sudden deafness is based on the promotion of increase in blood oxygen levels, including cochlear circulation. Based on these studies, hyperbaric oxygen therapy started to be used isolated or in association with other treatment approaches. An interesting application of hyperbaric oxygen therapy was described by MURAKAWA et al in 2000: the treatment of patients with sudden deafness already submitted to other forms of treatment but with no success. The authors argued that even in late stages, in which treatment in general is questioned, hyperbaric oxygen therapy could be relevant.

The treatment with Amidotrizoate (Hypaque ) described by Morimitsu, Ushisako (1988), owing to lack of convincing pathophysiological theory to justify its use, does not present other literature reports for the treatment of sudden deafness.

The use of Ginkgo biloba (Hoffmann, 1994) and pentoxiphylline (Leunig, 1995) has been recently proposed for the treatment of sudden deafness. Its use in management protocols, in association with other therapies, can be the route for more appropriate use of these drugs.

The latest news in management of sudden deafness is the therapy named HELP. Its action mechanism makes it logical and interesting. Maybe its use in selected cases, such as hyper-cholesterol patients, is the main advantage of this technique.

CLOSING REMARKS

Sudden deafness has been properly defined and conceptualized as sensorineural deafness of sudden onset and unknown etiology. The diagnosis seems to be easy, but it should be carefully investigated. A series of affections of well-defined etiologies can trigger sudden deafness. Upon simulating a picture of idiopathic deafness, they lack precise diagnosis and delay the appropriate treatment. The classical example is vestibular schwannoma, which triggers some sort of sudden deafness in 12 to 22% of the patients with the tumor. MRI or even angio-MRI are indispensable tests to support differential diagnosis of sudden deafness.

It is inevitable to be concerned about uncertainty in view of a case of sudden deafness as initial diagnosis. The severity of the situation and the frequent irreversibility of deafness justify the uncertainty of physician and patients. Since it has low incidence, few specialists are highly experienced in handling and managing the cases of sudden deafness. The uncertainty about etiopathogenesis and many treatment approaches available end up hindering decision-making. In most of the cases, outpatient treatment with corticoids and vasodilators is prescribed because it is easy to apply and of low cost. Therefore, we normally do not individualize each case within the probable situations and specific landmarks, which could lead to differentiated and more directed treatment to the most likely etiopathogenesis.

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1 Physician with the Service of Otorhinolaryngology, Hospital do Servidor Público Estadual, Sao Paulo.
2 Director, Service of Otorhinolaryngology, Hospital do Servidor Público Estadual, Sao Paulo.

Study conducted at the Service of Otorhinolaryngology, Hospital do Servidor Público Estadual, Sao Paulo.

Address correspondence to: Rua Jerônimo da Veiga, 164 conj. 9A - Sao Paulo - SP, CEP: 04536-000

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