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Auditory and vestibular disorders
Korean Journal of Audiology 2011;15(1):8-13.
Clinical and Audiologic Characteristics of Acute Low-Tone Sensorineural Hearing Loss: Therapeutic Response and Prognosis.
Hyeog Gi Choi, Kyoung Ho Park, Jae Hyun Seo, Dong Kee Kim, Sang Won Yeo, Shi Nae Park
Department of Otolaryngology-Head & Neck Surgery, The Catholic University of Korea College of Medicine, Seoul, Korea. snparkmd@catholic.ac.kr
Abstract
OBJECTIVES: This study was designed to observe the clinical and audiologic characteristics of patients diagnosed as low tone hearing loss (LHL) and to evaluate the treatment response and prognosis. SUBJECTS AND METHODS: A retrospective chart review of 61 patients who were diagnosed with LHL was performed. Result of various audiologic studies and therapeutic responses of medication have been evaluated. Data were statistically analyzed with variables such as age, sex, interval between onset and treatment, initial hearing levels, findings of electrocochleargraphy, and initial concomitant symptoms according to their treatment response.
RESULTS
Frequent chief complaints of LHL were tinnitus and earfullness. Tinnitus was usually matched at lower frequencies. Treatment with low-dose steroids, diuretics, and betahistine produced a high response rate of 79.4%. Complete response occurred in 49 of the 68 ears (72.1%) and partial response occurred in five of the 68 ears (7.4%). Fourteen of the 68 ears (20.6%) were in the non-responder group. Patients treated within 7 days after the onset of symptoms all showed complete response. Statistically significant prognostic factors affecting treatment response were age and intervals between onset and treatment (p<0.05).
CONCLUSION
Patients with acutely onset tinnitus or ear fullness should be carefully evaluated and promptly treated under the diagnosis of LHL.
Keywords: Low-tone hearing loss;Sensorineural;Prognosis

Address for correspondence : Shi-Nae Park, MD, PhD, Department of Otolaryngology-Head & Neck Surgery, The Catholic University of Korea College of Medicine, 505 Banpo-dong, Seocho-gu, Seoul 137-701, Korea
Tel : +82-2-2258-6215, Fax : +82-2-595-1354, E-mail : snparkmd@catholic.ac.kr

Introduction


Patients who complain of acute onset low-tone hearing loss (LHL) are relatively commonly encountered in daily clinical practice. They may frequently complain of diverse symptoms such as tinnitus, earfullness, autophony, and hearing impairment. The pure tone audiogram of these patients reveals sensorineuronal hearing loss restricted to the low frequency range. Abe presented the first detailed clinical review of patients with acute LHL.1) Studies of the pathophysiologic characteristics of acute LHL using the glycerol test and electrocochleogram led to the hypothesis that LHL might be caused by endolymphatic hydrops.2,3) Another hypothesis posited that the possible pathogenesis of LHL might be endolymphatic hydrops underlying autonomic imbalance and insufficient blood circulation.4 But a definite pathophysiology of LHL has not yet been established. Even though LHL might be associated with sudden deafness (SD) or Meniere's disease (MD), it also could be an entirely different clinical disease entity. To understand the disease entity of LHL more precisely and to stimulate further interest of this little known disease, we investigated the clinical and audiologic characteristics of 61 patients diagnosed with LHL and evaluated the responses to treatments that included low-dose steroids, hydrochlorothiazide, betahistine mesylate, ginko biloba extract, and nicergoline. Literature review concerning LHL is presented as well.

Subjects and Methods

Study design, treatment, and criteria
This study was designed as a retrospective chart review of 61 patients who visited our tertiary hospital between July 2001 and July 2006. It has been approved by the institutional review board of Seoul St. Mary's hospital (KC09RISI0287). They were diagnosed as LHL according to the following diagnostic criteria adopted from an established definition 5: 1) hearing loss is purely sensorineural in nature with normal tympanogram (type A); 2) average hearing threshold at the three low frequencies (125, 250 and 500 Hz) is 30 dB or more, and the average hearing threshold at the three higher frequencies (2,4, and 8 KHZ) is 20 dB or less; and, 3) the patient has no known etiologic factors that may cause low-tone sensorineuronal hearing loss as detected by routine clinical and radiologic examinations. The patients received their medical treatments at an outpatient clinic. Treatments consisted of prednisolone (SOLONDO
®, Yuhan Medica, Gunpo, Korea; 30 mg/day for 7 days) and the other drugs; hydrochlorothiazide (Dichlozid®, Yuhan Medica; 50 mg/day), betahistine mesylate (Meniace®, Dong Koo Pharmaceutical. Seoul, Korea; 30 mg/day), and microcirculation enhancers including ginko biloba extract (GINEXIN-F®, SK Chemical Life Science, Gyeonggi-Do, Korea; 160 mg/day) and nicergoline (Sermion®, Il Dong Pharmaceutical, Ansung, Korea; 30 mg/day).
Combination therapy were continued for seven days and then switched into the medication without prednisolone with the regular follow up of their hearing at 1-2 week interval until they showed improvement of hearing. The patients whose hearings were improved within three months were placed into the responder group and the others whose hearings did not show any improvement within three months were placed into the non-responder group. The responder group was subdivided into complete responder group who had normalization of hearing and partial responder group who showed 10 dB or more improvement at the three lower frequencies but did not reach normal hearing level at the end of treatment. To analyze the treatment response according to time interval between onset of disease and treatment, we grouped the patients as group 1 who received the treatment within 7 days of the onset of disease; group 2, whose time interval between onset and treatment were between 7 days and 1 month and; group 3 who had received the treatment more than 1month after the onset of disease. 

Audiologic study
Pure-tone air- and bone-conduction thresholds were measured at octave frequencies between 125 and 8,000 Hz in a soundproof chamber. Audiometry was performed at the time of first examination, and followed up at the first week, second week and 1 month. Long-term follow-up was done at 1–3 month intervals. Other audiologic studies including tympanogram, speech audiometry, tinnitogram, and electrocochleargraphy (ECoG) were initially performed.

Statistical analysis 
   Data were statistically analyzed with variables such as age, sex, interval between onset and treatment, initial hearing levels, findings of ECoG, and initial concomitant symptoms between groups. Significance was determined using t-test, Chi square test, and correlation analysis. The SPSS version 15.0 software was used for analyses. A level of significance 0 .05 was indicative of significance. 

Results

A total of 61 LHL patients were evaluated. Their ages ranged from 18-83 years with a mean age of 43.2±15.2 years. Follow-up period was 3-12 months. The patients were mainly female (n=43). The peak age of incidence was in the twenties for female and thirties for male (Fig. 1). The affected ear was the right ear in 32 cases, left ear in 28 cases and bilateral in four cases, for a total of 68 ears. One patient had multiple recurrences (four times) after treatment. Two patients were diagnosed with MD during the follow-up period. The time interval between the onset of ear symptoms and diagnosis ranged from 1-360 days. Four patients visited our clinic quite late after the onset of their symptoms which made the diagnosis range so wide, but the average time interval between onset of ear symptoms and our diagnosis of LHL in this study was 32.0 days. An interval of ≤1 month was observed in 79.1% of the cases and ≥1 month or more in 20.9 % of the cases. Frequent chief complaints were tinnitus (41.2%) and earfullness (39.7%), followed by autophony (10.3%) and hearing impairment (8.8%) (Fig. 2). Tinnitus was usually matched at lower frequencies (Table 1). Initial mean air conduction hearing levels of the patients with LHL were 44.1±6.0 dB at 125 Hz, 46±6.0 dB at 250 Hz, and 35.9±6.8 dB at 500 Hz (Fig. 3). The results of other audiologic studies such as speech discrimination score, ECoG, and tinnitogram are shown in Table 1. Only one patient showed an increment in the summating potential/action potential (SP/AP) ratio of ECoG (>0.4); the patient met the criteria of MD and was subsequently diagnosed with MD during the follow up period, 7 months after initial symptom of hearing loss.
Treatment with low-dose steroids, diuretics, and betahistine showed the relatively high response rate (79.4%, 54 of 68 ears)(Table 2). Complete responders comprised 49 of the 68 ears (72.1 %). Partial responders constituted five of 68 ears (7.4%). Fourteen of 68 ears cases (20.6%) were allocated to the non-responder group. Clinical factors affecting the results of therapeutic response were investigated between the responders and non-responders (Table 3). Statistically significant prognostic factors affecting therapeutic response to LHL were age and time interval between onset and treatment (p<0.05). Age showed a positive correlation with the state of final hearing loss at each frequency (125, 250, and 500 Hz, r=0.43, 0.33, and 0.27 respectively, p<0.05) and the time interval between onset and treatment was positively correlated with the state of final hearing loss at 125 and 250 Hz (r= 0.51 and r=0.43, p<0.05)(Table 4). Group 1, 2 and 3 showed 100%, 72.3% and 53.3% response rate respectively, which was significantly different prognosis according to time interval between onset of disease and treatment (p<0.01, Table 5).

Discussion

Low frequency sudden sensorineural hearing loss is a commonly encountered finding in otology practice. Although there have been many studies regarding the pathophysiology of LHL, the exact mechanism of LHL has remained elusive, and no international consensus on the general treatment of LHL has been reached. Some similarities of LHL to SD or MD such as an abrupt onset of hearing loss, accompanying ear fullness and tinnitus are apparent during course of the diseases, but the lack of vertigo and high recovery rate of hearing still differentiates LHL from SD or MD. However, diagnostic or therapeutic guidelines and consensus on this disease entity has not been established.6,7,8,9,10)
Clinical features of LHL include a predominance of female sufferers; peak incidence during the fourth decade of life; high incidence of tinnitus, earfullness, and/or autophony; and suspicion of bilateral involvement.8) In our study, patients with LHL were predominantly female preponderance and the peak age of incidence was in the twenties for females and in the thirties for males. But, bilateral involvement was observed only in four cases. Interestingly, the symptoms of LHL varied widely, and the chief complaint was not always hearing impairment. One study reported that over half of the patients had tinnitus, which often took the form of a low-pitched, motor-like tone.4) A sensation of earfullness and autophony is also frequently observed.4) Another study reported that the patient's complaints include ear fullness (89%), tinnitus (80%), autophony (63%), hearing loss (58%), and hyperacusis (43%).3) In our study, the frequent chief complaints were tinnitus and earfullness; tinnitus was usually at lower frequencies, consistent with a previous report.4) The feeling of earfullness occurs frequently in patients with acute LHL. For example, earfullness has been a cited initial symptom in 61.0% of patients with MD,11) 63.5% with acute low-tone sensorineural hearing loss,4) and 40.2% with sudden deafness.12) At present, the mechanism resulting in earfullness is unknown, and even the relationship between earfullness and the audiogram has yet to be elucidated. An association of earfullness and the low-frequency region was described, where hearing loss is relatively mild, and which disappear after the hearing threshold stabilized.13) These authors hypothesized that earfullness might originate from some functional factor rather than an organic lesion of the cochlea. In our study, since the two most frequently reported symptoms were earfullness and tinnitus, we suggest that the patients with acute onset earfullness and tinnitus should be carefully and promptly evaluated for their hearing loss at lower frequencies, and properly treated thereafter.
Many otolaryngologists have tried to explain the pathophysiology of LHL with the results of audiologic examinations.2,3,8,14) In addition to these, the glycerol test, vestibular evoked myogenic potentials, and the orthostatic test have been used to discover the pathophysiology and etiology of LHL.4,9) Especially, ECoG and the glycerol test are useful test tools for some study groups.3,5,14,15) In one of these studies, the SP/AP ratio was abnormally increased in 63% of LHL patients.3) In another study, the mean SP/AP ratio in LHL patients was 0.35±0.13 and the mean detection threshold of the cochlear microphonics was 32.0±9.4 dB normal hearing level, prompting the suggestion that the pathogenesis of LHL might arise from an endolymphatic hydrops with little or no impairment of hair cells that resembled early-stage MD.8) Presently, we did not observe the same findings of elevated SP/AP ratio in ECoG as in previous studies. Only one patient among 18 patients who has been checked ECoG during the symptomatic period displayed an elevated ECoG finding. Even though our follow-up period may not have been long enough to show the progression of LHL to MD, the observation of ECoG findings within normal range at the initial stage of LHL lead us to seek other possible pathomechanisms of LHL beyond endolymphatic hydrops. Only one of our patients who showed abnormal ECoG finding subsequently progressed to MD within a short period following LHL onset. Our results indicate that LHL might be a different disease entity from MD. However, we must not rule out the possible progression of LHL to MD once there is an abnormally elevated SP/AP ratio.
Since there is no international consensus on the treatment of LHL, various regimens and diverse modalities have been reported for the therapeutic strategies of LHL. One study reported that more than 70% of examined female patients and 80% of the male patients showed complete or partial hearing recovery when treated with vitamin B12 and adenosine triphosphate disodium, with only a few patients taking prednisolone at various dosages.4) Prednisolone forms the basis of an accepted regimen consisting of 40 mg/d on days 1-3; 30 mg/d on days 4-6; 20 mg/d on days 7-9; and 10 mg/d on days 10-12).3) Diuretics or vasodilators can also be used.3) In a study that examined the treatment outcome of intratympanic dexamethasone and hyaluronidase injection for 18 LHL patients whose hearing ability was still impaired after completion of the intravenous steroid therapy, 14 patients showed a significant improvement in hearing.16) Intratympanic dexamethasone injection therapy with oral prednisolone in LHL produces good recovery and marked improvement of motor-like tinnitus.14) Use of high-dose steroid therapy can cure some patients who have failed to recover using low-dose application of steroids. Collectively, the data supported the view that etiology of LHL involves an immune response.17) Only one regimen involving 70% Isosorbide (90 mL) administered orally every day has been reported to benefit LHL patients.9) Approximately 80% of LHL patients can be expected to experience complete or partial recovery,2,3,9,16) which is clearly a better result than is expected with SD or MD. We treated our LHL patients with a combination therapy of low-dose steroids, diuretics, betahistine and microcirculating enhancers, since possible mechanisms of LHL include endolymphatic hydrops and insufficient blood circulation. The same therapeutic regimen in our study enabled the analysis of prognostic factors for this combination therapy, which may help clarify the scientific clinical guidelines for the treatment of LHL. In this study, overall response rate of the combination treatment was as high as 80%, with no side effects or adverse effects. Limitation of this study is lacking proper control group, but, analysis of therapeutic efficacy of combination therapy here in our study will be an important basic data for the future study in the patients with LHL. Presently, we evaluated prognostic factors affecting treatment response in patients with LHL which were age and onset-treatment intervals. The treatment results were much better in younger patients and in patients with shorter intervals between onset and treatment. Our observations support the view that patients with acute tinnitus and earfullness should be considered as LHL patients and with LHL, early combination treatment being more effective than delayed treatment. 

Conclusion

Although LHL frequently shows somewhat similar clinical and audiologic characteristics to mild form of sudden deafness or early stage MD, it is thought to be a different entity with better medical treatments response and prognosis compare to SD or MD. For the patients with acute ear fullness and tinnitus, LHL should always be considered. Its early diagnosis and prompt treatment might be the one approach guideline for this less known disease entity. Further studies on pathogenesis of LHL are needed to build up the consensus on the disease entity and on the standard treatment modality. 


REFERENCES
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