J Huazhong Univ Sci Technol[Med Sci] DOI 10.1007/s11596-017-1726-8 37(2):264-270,2017 J Huazhong Univ Sci Technol[Med Sci] 37(2):2017
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Assessment of Balance and Vestibular Functions in Patients with Idiopathic Sudden Sensorineural Hearing Loss* Jia LIU (刘 佳)†, Ren-hong ZHOU (周任红)†, Bo LIU (刘 波), Yang-ming LENG (冷扬名), Jing-jing LIU (刘晶晶), Dong-dong LIU (刘东冬), Su-lin ZHANG (张甦琳)#, Wei-jia KONG (孔维佳)# Department of Otolaryngology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022,China © Huazhong University of Science and Technology and Springer-Verlag Berlin Heidelberg 2017
Summary: This study investigated the relationship among the severity of hearing impairment, vestibular function and balance function in patients with idiopathic sudden sensorineural hearing loss (ISSNHL). A total of 35 ISSNHL patients (including 21 patients with vertigo) were enrolled. All of the patients underwent audiometry, sensory organization test (SOT), caloric test, cervical vestibular-evoked myogenic potential (cVEMP) test and ocular vestibular-evoked myogenic potential (oVEMP) test. Significant relationship was found between vertigo and hearing loss grade (P=0.009), and between SOT VEST grade and hearing loss grade (P=0.001). The abnormal rate of oVEMP test was the highest, followed by the abnormal rates of caloric and cVEMP tests, not only in patients with vertigo but also in those without vertigo. The vestibular end organs were more susceptible to damage in patients with vertigo (compared with patients without vertigo). Significant relationship was found between presence of vertigo and SOT VEST grade (P=0.010). We demonstrated that vestibular end organs may be impaired not only in patients with vertigo but also in patients without vertigo. The cochlear and vestibular impairment could be more serious in patients with vertigo than in those without vertigo. Vertigo does not necessarily bear a causal relationship with the impairment of the vestibular end organs. SOT VEST grade could be used to reflect the presence of vertigo state in the ISSNHL patients. Apart from audiometry, the function of peripheral vestibular end organs and balance function should be evaluated to comprehensively understand ISSNHL. Better assessment of the condition will help us in clinical diagnosis, treatment and prognosis evaluation of ISSNHL. Key words: idiopathic sudden sensorineural hearing loss; sensory organization test; cervical vestibular-evoked myogenic potential; ocular vestibular-evoked myogenic potential
Idiopathic sudden sensorineural hearing loss (ISSNHL) is clinically defined as sensorineural hearing loss of sudden onset with unknown origin[1]. Consensus on the pathogenesis of sudden deafness has not yet been reached. The most commonly cited theories for the etiology of idiopathic sudden hearing loss are viral infection, ischaemia, autoimmune reaction and inner ear – membrane rupture[2 6]. Despite its dominant cochlear symptoms, ISSNHL may affect the vestibular partition, clinically resulting in vertigo or tinnitus. A vestibular test battery has been developed to comprehensively evaluate vestibular impairment. The test battery involves, among others, caloric Jia LIU, E-mail:
[email protected]; Ren-hong ZHOU, E-mail:
[email protected] † The two authors contributed equally to this work. # Corresponding authors, Wei-jia KONG, E-mail:
[email protected]; Su-lin ZHANG, E-mail:
[email protected] * This project was supported by grants from the National Twelfth Five-Year Science and Technology Support Program of China (No. 2012BAI12B02), and the National Eleventh Five-Year Science and Technology Support Program of China (No. 2007BAI18B13).
test, cervical vestibular-evoked myogenic potential (cVEMP), ocular vestibular-evoked myogenic potential (oVEMP), video head impulse test (vHIT) and rotation chair. In this test battery, the caloric test is most frequently used for the functional assessment of horizontal semicircular canal, since its irrigation to the ears produces a unilateral stimulation of the peripheral vestibular organ[7]. VEMPs, measured by putting electromyographic (EMG) electrodes either over the tensed sternocleidomastoid (SCM) muscles for the cVEMP or over the tensed muscles beneath the eyes for the oVEMP, are short-latency potentials evoked by bone-conducted vibration (BCV), air-conducted sound (ACS) or galvanic stimulation[8]. cVEMP can assess the sacculo-collic reflex and can be easily recorded in the cervical muscles[9]. As a measure of the crossed vestibulo-ocular reflex, oVEMP can be recorded from extraocular muscles[10, 11]. cVEMP is widely employed for the functional assessment of saccular and inferior vestibular nerve, while oVEMP is used clinically to evaluate utricular function and superior vestibular nerve function[8, 12]. Vestibular disorder tends to bring about balance problems. The human balance system is a complicated system that involves integration of information from visual, vestibular and somatosensory systems[13]. The sensory organisation test (SOT) is used clinically to
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evaluate postural balance function under stimulations of sensory system[14]. SOT involves quantitative and objective assessment of not only the different sensory and motor components in the body balance system but also the integration and adaptive mechanisms in the central nervous system[15]. Iwasaki et al, by using cVEMP and caloric tests, examined the lesion site of vestibular end organs in ISSNHL with vertigo and suggested that the saccule was involved more frequently than the horizontal semicircular canal[16]. Korres et al investigated patients with ISSNHL and found a significant correlation between abnormal cVEMP or caloric test results and profound hearing loss[17]. Fujimoto et al studied the extent of vestibular lesions using cVEMP, oVEMP and caloric tests, and found that the vestibular end organs closest to the cochlea tended to be more susceptible in ISSNHL patients with vertigo[18]. Niu et al, by using cVEMP, oVEMP and caloric tests, demonstrated that the presence of vertigo or abnormal caloric test results were associ ated with profound hearing loss in ISSNHL patients[19]. A number of recent studies, by using neuroimaging, suggested that brain structure was gradually impaired after the deterioration of ISSNHL[20–22]. The onset of ISSNHL caused maladaptive cortical reorganization in the ipsilateral auditory cortex and appreciable decrease in the area of contralateral auditory cortex within the acute period[20–22]. Balance function involves assessment of not only visual, vestibular and somatosensory sensation, but also the integration in the central nervous system[15]. So far, no studies examined the balance function in ISSNHL patient with or without vertigo. In this study, we used audiometry, vestibular func-tion tests (cVEMP, oVEMP and caloric tests) and bal-ance test (SOT) in combination, with an attempt to find the relationship among the severity of hearing impair-ment, vestibular function and balance function. 1 PARTICIPANTS AND METHODS 1.1 Participants Participants were subjected to audiometric, vestibular and balance function tests at the Department of Otolaryngology, Union Hospital, Tongji Medical College of Huazhong University of Science and Technology, Wuhan, China. Between April and November 2016, the records of 35 consecutive patients with unilateral ISSNHL were reviewed retrospectively. Patients were eligible for enrollment if they had been diagnosed with ISSNHL against the criteria proposed by Stachler et al in 2012[1]. The participants (including 26 females and 9 males, 21 with vertigo and 14 without vertigo) were aged between 15–67 years (mean age: 41.9±13.8 years). The course of disease lasted from 1 to 30 days (mean course: 12.6±10.1 days). Participants were included if the results of audiometric, caloric, cVEMP and oVEMP tests were normal on the contralateral side, which could eliminate the influence of advanced age. Exclusion criteria included: (1) Candidates were diagnosed with benign paroxysmal positional vertigo (BPPV) by Dix-Hallpike test and Roll test; (2) Candidates had multiple attacks of hearing loss
265 and vertigo, such as Meniere's disease or migraine; (3) Central nervous system or retrocochlear lesions, such as acoustic neuroma, were revealed by auditory brain-stem response and MRI; (4) Candidates had previous history of brain trauma, otitis media or tinnitus; (5) Candidates had previous history of otological, ophthalmological, orthopedic, musculoskeletal and neurological disorders. This study was conducted in strict accordance with the tenets of the Declaration of Helsinki and approved by the Ethics Committee of Wuhan Union Hospital of Tongji Medical College of Huazhong University of Science and Technology, Wuhan, China. Written informed consents were obtained from all participants. 1.2 Audiometry Audiometry instrument used was Madsen Electronics Orbiter 922 Version 2 Clinical Audiometer (Otometrics A/S, Taastrup, Denmark). According to the guideline of diagnosis and treatment of sudden deafness (2015), the audiographic results were categorized as low-frequency hearing loss, high-frequency hearing loss, flat-type hearing loss and profound hearing loss in terms of the frequency and degree of hearing loss[23]. For low-frequency hearing loss, pure tone average (PTA) was calculated as the average hearing thresholds at 250, 500 and 1000 Hz; for high-frequency hearing loss, PTA was computerized as the average hearing thresholds at 2000, 4000 and 8000 Hz; for flat-type hearing loss and profound hearing loss, PTA was expressed as the average hearing thresholds at 125, 250, 500, 1000, 2000, 4000 and 8000 Hz. If the hearing threshold at a certain frequency was off the scale, the threshold of the frequency was estimated to be the maximum sound level generated by the audiometer plus 10 dB HL. According to the hearing loss classification of World Health Organization (WHO) standard in 1997, hearing loss was graded in terms of PTA as follows: grade 1, mild and moderate (< 60 dB HL); grade 2, severe (61–80 dB HL); grade 3, profound (≥80 dB HL). 1.3 Caloric Test The caloric test was employed to evaluate the lateral semicircular canal function and identify the presence and side of a peripheral vestibular disorder[7]. We used videonystagmography (VNG) (VisualEyesTM VNG, Micromedical Technologies Inc., USA) to record horizontal eye movements during the caloric test. Before the test, the spontaneous nystagmus was recorded. The caloric test was performed by an air caloric irrigator system (Air Fx from Micromedical Technologies Inc., USA). The temperature of the warm and cool air was 50°C and 24°C, respectively. The unilateral weakness (UW) was used to quantify the difference between the caloric responses of the two ears and was calculated by Jongkees’ formula[24]. An abnormal caloric result was defined as a |UW%| greater than 25%[25]. 1.4 cVEMP cVEMP can be employed for evaluating saccular and/or inferior vestibular pathway[8, 12, 26]. Participants were asked to sit on a chair and rotate their head to the contralateral side to activate SCM muscles. The EMG signals were recorded by the Eclipse system (from Interacoustics A/S, Middelfart, Denmark). An active electrode was placed on the upper third of the ipsilateral
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conditions are listed in table 1[33, 34]. The equilibrium score under each condition was calculated by averaging the scores of three consecutive trials. The subject’s ability to use input from the vestibular system (VEST ratio) to keep balance was calculated by dividing the score in condition 5 by the score in condition 1[32]. If VEST ratio >0.57, SOT VEST grade was defined as normal and if VEST ratio <0.577, SOT VEST grade was seen as abnormal[32]. 1.7 Data Analysis Data were statistically analyzed by SPSS software package (version 24.0 for Windows; SPSS Inc., USA). Chi-square test was used to identify the possible relationships among different variables, and a P<0.05 was considered to indicate a statistically significant difference.
SCM muscles, a ground electrode was put on the forehead, and a reference electrode was on the sternoclavicular junction[9]. Stimuli were produced by a customized VEMP software package (OtoAccess, from Interacoustics A/S, Middelfart, Denmark). We utilized ACS tone bursts (500 Hz, 5 ms) as stimuli presented monaurally at the level of 100 dB nHL through earphones. Each tracing session included 100 stimuli at least on average. When each run was finished, the peaks of p13 and n23 were labeled. cVEMP responses were seen as abnormal if: (1) The amplitude asymmetry ratio (AR) was more than the mean of normal range±2×standard deviation (SD) (the AR was greater than 36% in our hospital); (2) The peak-to-peak cVEMP amplitude was absent or reduced; (3) cVEMP threshold shift was out of the range between the mean of normal range±2×SD (delayed response)[27]. 1.5 oVEMP oVEMP can be used for assessing utricular and/or superior vestibular pathway[8, 12]. oVEMP test was performed by the same system used for recording cVEMP. Signals obtained under the eye contralateral to the stimulated ear were recorded and assessed. During the test, participants sat on a chair and were instructed to stare up at a red spot fixed on the wall at midline in front of them[28, 29]. The stare forced the participants to elevate and maintain their gaze up to approximately 30° above the horizontal plane during each session of the test[30]. An active electrode was positioned on the contralateral inferior oblique muscles, a ground electrode was applied on the forehead, and a reference electrode was placed on the chin[31]. The stimuli in oVEMP were the same as those in cVEMP. When each run was finalized, the peaks of p10 and n15 were labeled. oVEMP responses were considered to be abnormal if: (1) Biphasic waveform of oVEMP was absent after at least 50 responses; (2) AR was greater than the mean of normal range±2×SD (the AR was greater than 40% in our hospital)[27]. 1.6 SOT SOT was used to assess the continuous balance performance during a sequence under six different sensory task conditions[32]. Participants stood on a SMART Equitest platform (NeuroCom International Inc., Clackamas, USA) and were asked to stand upright and maintain balance when the test was going on. Six test
2 RESULTS 2.1 Relationship between Hearing Loss and Vestibular or Balance Function Chi-square test was used to identify the possible relationships between hearing loss and the following factors: age, gender, the presence of vertigo or spontaneous nystagmus, caloric test results, cVEMP, oVEMP or SOT VEST grade. Significant relationship was found between vertigo and hearing loss grade (P=0.009), and found between SOT VEST grade and hearing loss grade (P=0.001). In addition, significant difference in presence of vertigo was found between patients with grade 1 hearing loss and those with grade 3 hearing loss (P=0.009). This result suggested that the hearing loss was worse in ISSNHL patients with vertigo than in those without. In patients with grade 1 hearing loss, 4 patients (28.6%) had vertigo; in patients with grade 2 hearing loss, 4 (80%) had vertigo; in patients with grade 3 hearing loss, 13 (81.3%) had vertigo. These results suggested that the majority of the ISSNHL patients with vertigo had severe and profound hearing loss. Furthermore, significant difference in SOT VEST grade was revealed between patients with grade 1 hearing loss and those with grade 2 hearing loss (P=0.006), and between patients with grade 1 hearing loss and those with grade 3 hearing loss (P=0.007). Those results suggested that the patients with mild and moderate hearing loss tended to have normal SOT VEST grade.
Table 1 Six sensory conditions in SOT Condition 2 Condition 3 Condition 4
Inputs
Condition 1
Condition 5
Condition 6
Visual input
9
×
Disturbed
9
×
Disturbed
Somatosensory input
9
9
9
Disturbed
Disturbed
Disturbed
Vestibular input
9
9
9
9
9
9
9: Input was applied; ×: No input was applied; Disturbed: Input was disturbed.
2.2 Vestibular Function in Patients with or without Vertigo The abnormal rates of oVEMP, caloric and cVEMP tests in patients with and without vertigo are shown in table 2 and in fig. 1. Vestibular impairment of various degrees in patients with or without vertigo is shown in table 3 and fig. 2. The results showed that the abnormal
rate of oVEMP test was the highest, followed by the abnormal rates of caloric and cVEMP tests, not only in patients with vertigo but also in patients without vertigo. Compared with patients without vertigo, the vestibular end organs were more susceptible to damage in patients with vertigo. When vestibular impairment was measured in terms of the number of the abnormal results, most of
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the patients with vertigo were in groups that had two or three abnormal results. On the other hand, most of the patients without vertigo were in relatively mild damage groups. Vestibular end organs might be impaired in ISSNHL patients with and without vertigo. 2.3 Balance Function in Patients with or without Vertigo Chi-square test was employed to identify the possible relationships between the presence of vertigo and the following factors: the presence of spontaneous nystagmus, caloric test results, cVEMP, oVEMP or SOT VEST grade. Significant relationship was found between presence of vertigo and SOT VEST grade (P=0.010).
Vertigo
Fig. 1 The abnormal rates of oVEMP, caloric and cVEMP tests in patients with and without vertigo
Table 2 The abnormal rates of oVEMP, caloric and cVEMP tests in patients with and without vertigo oVEMP Caloric cVEMP
With (n=21)
76.2%
66.7%
57.1%
Without (n=14)
42.9%
35.7%
35.7%
Vertigo
Table 3 Vestibular impairment of various degrees in patients with or without vertigo Grade 1 Grade 2 Grade 3 Grade 4
Vertigo (n=21)
19.0%
4.8%
33.3%
42.9%
Without (n=14)
42.9%
14.3%
28.5%
14.3%
Grade 1: three normal results; Grade 2: one abnormal result; Grade 3: two abnormal results; Grade 4: three abnormal results Table 4 Vestibular impairment of various degrees in patients with abnormal SOT VEST grade Spontaneous nystagmus Grade 1 Grade 2 Grade 3 Grade 4 Without (n=8)
25%
12.5%
25%
37.5%
With (n=6)
16.7%
0
16.7%
66.7%
Total (n=14)
21.4%
7.2%
21.4%
50%
Grade 1: three normal results; Grade 2: one abnormal result; Grade 3: two abnormal results; Grade 4: three abnormal results
shown in table 4 and fig. 3.
Fig. 2 Vestibular impairment of various degrees in patients with or without vertigo Grade 1: three normal results; Grade 2: one abnormal result; Grade 3: two abnormal results; Grade 4: three abnormal results
The presence of vertigo was taken as the golden standard for the calculation of the sensitivity and specificity of SOT VEST grade. The sensitivity of SOT VEST grade was 57.1%, and the specificity of SOT VEST grade was 85.7%. Vestibular impairment of various degrees in patients with abnormal SOT VEST grade is
Fig. 3 Vestibular impairment of various degrees in patients with abnormal SOT VEST grade Grade 1: three normal results; Grade 2: one abnormal result; Grade 3: two abnormal results; Grade 4: three abnormal results
3 DISCUSSION Accurate evaluation of ISSNHL with or without vertigo may help us better understand the etiology of the disease. In this study, we demonstrated that SOT VEST
268 grade could be used to reflect the presence of vertigo state in the ISSNHL patients. Vestibular end organs may be impaired not only in patients with vertigo but also in patients without vertigo. The cochlear and vestibular impairment could be more serious in patients with vertigo than in those without vertigo. In fact, vertigo, as a common symptom of ISSNHL, does not necessarily bear a causal relationship with the impairment of the vestibular end organs. Compared with the patients without vertigo, the hearing loss was worse in patients with vertigo, most of patients with vertigo (81%) suffering from severe and profound hearing loss. Our study showed that the cochlear impairment was worse in patients with vertigo than in those without vertigo. The results were consistent with previously reported findings. Noury and Katsarkas reported that vertigo in sudden deafness was more common in patients with profound hearing loss[35]. Another study involving 1313 cases of sudden deafness and a research by Cho and Choi also reported similar results[36, 37]. PTA in our study was calculated in terms of audiographic results. At present, it is generally believed that low-frequency hearing loss is caused by the damage of the apical cochlear turn and high-frequency hearing loss is brought about by the basal cochlear turn damage[38]. In addition, the basal cochlear turn anatomically could be more proximal to the vestibular end organs than the apical cochlear turn[39]. Therefore, the patients with high-frequency hearing loss tend to suffer from more vertigo attacks. However, other studies showed the otherwise, suggesting that low-frequency hearing loss is associated with endolymphatic hydrops, which is similar to a pathological feature of Meniere’s disease at the early stage, and the patients with a low frequency hearing loss may have more vertigo episodes[40–42]. In view of the two diametrically opposite hypotheses, we did not classify the patients with vestibular and balance disorders in terms of audiographic results. Moreover, we found that the patients with mild and moderate hearing loss tended to have normal SOT VEST grades, indicating that patients with severer cochlear impairment tended to develop balance disorder. The finding suggests that clinicians should pay more attention to the balance function of the ISSNHL patients. The abnormal rate of oVEMP test was the highest, followed by the abnormal rates of caloric and cVEMP tests, not only in patients with vertigo but also in those without vertigo, indicating that utricle and horizontal semicircular canal might be more prone to damage than saccule. Goebel et al suggested that the bony canal of the superior vestibular nerve is longer than the singular nerve canal[43]. Additionally, the superior vestibular nerve and arteriole go through a relatively narrower passage than the singular nerve[43]. From an anatomic point of view, this renders the superior division of the vestibular nerve more susceptible to entrapment and possible ischemic labyrinthine changes[43]. This might explain the vulnerability of utricle and horizontal semicircular canal that connect superior vestibular nerve. Inagaki et al found, by anatomical analysis of temporal bone, one SSNHL patient with vertigo had deposits in the utriculus[44]. Manzari et al suggested that the impairment of utricle alone was also able to induce spontaneous nys-
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tagmus in the ISSNHL patients with vertigo[45]. All of the aforementioned studies suggested that utricle is more susceptible to damage in the ISSNHL patients. However, Fujimoto et al suggested that saccule might be more easily damaged than utricle and horizontal semicircular canal[18]. In addition, Schuknecht and Donovan found hair cells of the organs of Cort in saccule were more easily damaged when they studied temporal bone pathologies of patients with ISSNHL[46]. Compared with the study by Fujimoto et al, which only included the ISSNHL patients with vertigo, our study included ISSNHL patients without vertigo. Besides, caloric test (They used ice water, while we employed cold and hot air), cVEMP (Their patients took supine position and ours took sitting position), oVEMP (Their subjects took supine position with BCV, and our patients took sitting position with ACS), the course and treatment of the disease, the test methods, and determination of results were different in both studies, which may account for the discrepancies between the two studies. Compared with patients without vertigo, patients with vertigo were more likely to develop damage of vestibular end organs. When the degree of vestibular impairment was measured in terms of the number of the abnormal results, we found that most of the patients with vertigo were in groups that yielded two or three abnormal results, while most of the patients without vertigo were in relatively mild damage groups. The foregoing results indicated that the degree of vestibular impairment was much severer in patients with vertigo than in those without vertigo. As discussed before, the cochlear impairment was much worse in patients with vertigo. The cochlea is topographically close to the vestibule, so the vestibular impairment would be much worse in patients with vertigo. In addition, Korres et al exhibited that the severity of cochlear damage tends to positively correlate with the extent of the inner ear lesion (cochlear lesion, otolithic organ lesion and horizontal semicircular lesion)[17], which was coincident with our result. Nonetheless, Inagaki et al reported that the vestibular system experienced identical changes in sudden deafness patients with and without vertigo[44]. And there existed no remarkable difference in the density of vestibular hair cells between patients with vertigo and those without vertigo[44]. So far, no consensus has been reached on the relationship between the presence of vertigo and the severity of vestibular impairment. Vestibular end organs might be impaired both in ISSNHL patients with and without vertigo. Vertigo is not a disease entity, but, rather, a symptom caused by multiple pathologies. The most commonly cited etiology of ISSNHL is viral infection or ischaemia[2–4]. Viral infection or viral reactivation within the inner ear, and lack of collateral blood supply can cause cochlear inflammation and/or damage to critical inner ear structures. And this could explain why cochlea and vestibule are usually impaired simultaneously. However, some ISSNHL patients are without peripheral vestibular impairment. Khetarpal investigated the histopathologic characteristics of the temporal bone in sudden deafness patients with and without vertigo, and didn’t find any vestibular impairment[47]. So he hypothesized that vertigo in ISSNHL was caused by transmission of biochemical changes in inner
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ear fluid from the cochlea to the vestibular end organs[47]. This biochemical changes might result from the autoimmune reaction or inner ear membrane rupture near the vestibule. In addition, we did not examine the function of vertical semicircular canals in this study, so the function of vertical semicircular canals in patients remains unknown. Furthermore, Khetarpal found no direct relationship between the presence of vertigo and damage of vestibular end organs[47]. Inagaki et al also found that there was no remarkable difference in the density of vestibular hair cells between patients with vertigo and those without vertigo[44]. These findings indicated that some of the ISSNHL patients without vertigo might have vestibular impairment and heed should be paid to the vestibular and balance function in ISSNHL patients with and without vertigo. The balance function test showed that the specificity of SOT VEST grade for ISSNHL patients with vertigo was quite high (85.7%). ISSNHL patients with vertigo tended to have abnormal SOT results. This finding was consistent with the severe vestibular dysfunction found in ISSNHL patients with vertigo. When we classified the patients with abnormal SOT VEST grade in terms of severity of vestibular impairment, most patients, with and without spontaneous nystagmus, had three abnormal test results. This result also confirmed that the sensitivity of SOT VEST grade was not high (57.1%), and SOT VEST grade could only detect the patients with severe vestibular impairment. This study showed that, for some ISSNHL patients without vertigo, their vestibular end organs were not impaired, but the balance function was abnormal, suggesting that the balance disorder might be a sub-clinical condition and balance function entails an integration of visual, vestibular and somatosensory systems. Study by Halmagyi et al suggested that for the vestibular lesion affecting only one isolated region of the inner ear, the absence of adequate input from this region and the presence of intact input from other end organs may impact on the overall integration of all vestibular sensory information and may generate an internal mismatch of sensory input in central vestibular pathways and this sensory mismatch may induce the balance disorder[48]. The balance function changes with progression of disease, and its prognosis and rehabilitation which may vary with different patients needs to be further studied. One limitation of the study was that we didn’t examine the function of vertical semicircular canals. Large population, multi-setting, controlled studies with long-term follow-up will be warranted. To sum up, besides audiometry, the function of peripheral vestibular end organs and balance function should be evaluated to comprehensively understand ISSNHL. Better assessment of the condition will help us in clinical diagnosis, treatment and prognosis evaluation of ISSNHL. Conflict of Interest Statement The authors declare that they have no conflicts of interest. Acknowledgments We are indebted to all the staff in Department of Otolaryngology, Wuhan Union Hospital of Tongji Medical College of
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