The Relationship between the Characteristics of Tinnitus and the Hearing Curative Effect of Sudden Deafness

Sudden deafness refers to sensorineural hearing loss which occurs suddenly within 72 h and has unknown cause [Editorial Committee of the Chinese Journal of Otolaryngology, Head and Neck Surgery, 2015]. Tinnitus is the most common complication of sudden deafness, especially the only or primary complaint of mild to moderate hearing loss patients. According to previous literature reports, 70–90% of sudden deafness patients have tinnitus [Mamak et al., 2005; Schreiber et al., 2010; Michiba et al., 2013; Lee et al., 2015]. Many patients sometimes do not pay attention to the hearing impairment but will be forced to tinnitus trouble to medical treatment. The prognostic value of tinnitus in hearing effect has been controversial. There are many studies on tinnitus and tinnitus as a prognostic factor for sudden deafness [Hikita-Watanabe et al., 2010; Wen et al., 2014; Lee et al., 2015; Rah et al., 2015]. It has also been reported that tinnitus is a positive factor for hearing prognosis in sudden deafness [Hikita-Watanabe et al., 2010; Nogueira-Neto et al., 2016]. The absence of tinnitus may indicate severe cell damage or cell death; therefore, the presence of tinnitus may be a marker of impaired cellular activity [Lionello et al., 2015]. It was found that the tinnitus of patients with sudden deafness was very strange. In the past, the tinnitus of sudden deafness was assessed by questionnaires, such as tinnitus handicap inventory (THI) [Newman et al., 1996] and tinnitus functional index [Meikle et al., 2012]. This paper that we are now publishing reviewed the data of 285 cases of sudden deafness and analyzed the relationship between the characteristics of tinnitus and the hearing effect, so as to provide some ideas for clinical examination of tinnitus diagnosis and prognosis evaluation of sudden deafness.

This retrospective research was carried out at E.N.T. Department of Tongde Hospital, Zhejiang Province according to the principles of the Declaration of Helsinki. Approval for the study was given by the Ethics Committee of Tongde Hospital, Zhejiang Province, and the approval No. is ZTDKSZ (2022) No. 083.

Participants were referred to E.N.T. Department of Tongde Hospital, Zhejiang Province from March 2018 to March 2021. Patients with sudden deafness were diagnosed according to Diagnosis basis and treatment guidelines for sudden deafness [Editorial Committee of the Chinese Journal of Otolaryngology, Head and Neck Surgery, 2015]. Tinnitus excludes objective tinnitus such as middle ear effusion or pus flow, external auditory meatus pus activity, or chronic old tinnitus due to non-sudden hearing loss. Patients with sudden deafness who did not have the pure tone audiometry data and tinnitus matching data before and after treatment were excluded. The patients were treated according to the 2015 edition guidelines. All patients were given glucocorticoids (methylprednisolone 40 mg/day was injected intravenously for 5 days), improved microcirculation drugs (e.g., ginkgo biloba extract), reduced fibrinogen drugs (e.g., bactrase), antioxidants (e.g., lipoic acid), combined with hyperbaric oxygen, traditional Chinese medicine, and physiotherapy.

The patients were divided into two groups: (1) no tinnitus was found at morbidity and (2) no tinnitus was found before, and tinnitus was found at diagnosis. 285 cases (330 ears) were selected, including 177 ears without tinnitus and 153 ears with tinnitus. Among them, 120 males and 165 females aged 14–87 years. Among them, 137 cases were left tinnitus, 103 cases were right tinnitus, and 45 cases were bilateral tinnitus.

Pure tone audiometry is conducted in standard soundproof room using an Otometrics Astera audiometer, and seven octave frequencies of 125 Hz–8,000 Hz are routinely tested, and half octave frequency (such as 750 Hz, 1,500 Hz, 3,000 Hz, 6,000 Hz) is added if necessary. The audiogram of patients with sudden deafness was collected at diagnosis and after treatment.

Tinnitus matching (psychoacoustic characteristics of tinnitus) includes tinnitus frequency matching and tinnitus loudness matching. The sound types were pure tone, rhyme, narrowband noise, and white noise (tinnitus patients matched with white noise were not included in the study because of frequency specificity lacking, the effects of different types of tinnitus sounds were not discussed in this paper).

Patients were asked to determine the tone that best matched their tinnitus. Each tone is presented at a sensory level of 10 dB SL. The two tones are presented alternately, allowing patients to point out which one is closest to the pitch of their tinnitus [Shekhawat et al., 2014]. The closest tinnitus frequency in 125 Hz, 250 Hz, 500 Hz, 750 Hz, 1,000 Hz, 1,500 Hz, 2,000 Hz, 3,000 Hz, 4,000 Hz, 6,000 Hz, 8,000 Hz was finally determined. Then patients were asked to look for the same loudness as tinnitus and finally to determine the closest tinnitus loudness sensory level (dB SL).

Tinnitus frequency was divided into three groups: (1) low frequency tinnitus: 125–500 Hz (2) intermediate frequency tinnitus: 750–2,000 Hz, and (3) high frequency tinnitus: 3,000–8,000 Hz [Zhong et al., 2015; Zhong et al., 2018]. Tinnitus loudness was divided into two groups: (1) 1–10 dB SL and (2) >10 dB SL.

Evaluation criteria [Editorial Committee of the Chinese Journal of Otolaryngology, Head and Neck Surgery, 2015] of hearing curative effective rate for sudden deafness were as follows:

1. Completely effective: the hearing of impaired frequency recovered to normal, or reached the level of healthy ears, or reached the level before the disease.

2. Obvious effective: the hearing of impaired frequency is improved by 30 dB.

3. Effective: the hearing of impaired frequency is improved by 15–30 dB on average.

4. Not effective: The average hearing improvement in impaired frequency is less than l5 dB.

The total effective rate is calculated by adding the completely effective rate, the obvious effective rate, and the effective rate.

The degree of hearing loss was classified into four groups using the PTA of the affected ear: mild (PTA of 15–39 dB), moderate (PTA of 40–59 dB), severe (PTA of 60–79 dB), and profound (PTA more than 80 dB). According to the frequency and degree of hearing loss involved, sudden deafness is divided into different shapes of the audiogram: high frequency descending type, low frequency descending type, flat descending type, and total deafness type [Editorial Committee of the Chinese Journal of Otolaryngology, Head and Neck Surgery, 2015].

IBM SPSS version 22 was used for all statistical analyses. Age data are presented as mean ± standard deviation, and t test is applied. Categorical variables were recorded with number of cases (n) and percentages (%). The χ² analysis was used to evaluate the significant difference between groups. In the post hoc analysis, the Bonferroni correction was performed for multiple comparisons. A p value <0.05 was considered significant.

The total effective rate of the hearing efficacy in this study was 69.1% (228/330). Among 330 ears enrolled, there were 177 ears without tinnitus and 153 ears with tinnitus. Table 1 shows that prognostic factors such as the age, the sex, the presence of vertigo in the moment of the sudden deafness, the degree of hearing loss, and the shape of the audiogram were not associated with the hearing efficacy in relation to the characteristics of the tinnitus. Table 2 shows there was no significant difference (p > 0.05) between the hearing efficacy of sudden deafness with tinnitus and without tinnitus.

Table 3 shows that low frequency tinnitus accounts for 53.6% (82/153), intermediate frequency tinnitus accounts for 7.2% (11/153), and high frequency tinnitus accounts for 39.2% (60/153). The total effective rate of sudden deafness with high frequency tinnitus was the lowest, and there was significantly different with the group without tinnitus and also significantly different compare with low frequency tinnitus (p < 0.05).

Table 4 shows that tinnitus loudness of 1–10 dB SL accounts for 80.4% (123/153) and >10 dB SL accounts for 19.6% (30/153). There was no significant difference in hearing effective rate between the patients with different tinnitus loudness (p > 0.05). Table 5 shows that there was a significant difference between the distributions of tinnitus frequency in four different shapes of the audiogram.

In recent years, the incidence of sudden deafness in China has been increasing, and there have been many multivariate analyses on the clinical efficacy of sudden deafness patients [Zhang et al., 2015; Sun et al., 2018]. The influence of tinnitus on hearing effect of sudden deafness is different in different literatures. Most scholars think that tinnitus has no influence on prognosis of sudden deafness. Some scholars think that tinnitus has poor prognosis, others think tinnitus symptoms indicate that the function of inner ear hair cells is still alive and predict the possibility of hearing recovery is greater [Sun et al., 2018].

At present, the diagnosis criterion of tinnitus degree is the subjective grade of tinnitus (THI). The same degree of tinnitus may have different subjective feelings for different patients. Studies [Nogueira-Neto et al., 2016] on the degree of tinnitus (subjective grade of tinnitus) have shown that sudden deafness with tinnitus represents a certain degree of disorder that negatively affects the quality of life of patients. After treatment, the discomfort due to tinnitus assessed by THI was reduced. The severity of tinnitus assessed by THI was not proportional to the degree of hearing loss and was not a prognostic factor for hearing improvement. Therefore, the THI classification is not used to evaluate the curative effect of sudden deafness. However, there is no related study to evaluate the curative effect of sudden deafness by using the psychoacoustic characteristics such as tinnitus frequency and tinnitus loudness. This study retrospectively analyzed 285 patients with sudden deafness to study the relationship between tinnitus psychoacoustic characteristics and hearing curative effect, and further provide more scientific judgment for prognosis evaluation of sudden deafness.

There was no significant difference of prognostic factors between the sudden deafness patients with and without tinnitus (p > 0.05). For example, the age, the sex, the presence of vertigo in the moment of the sudden deafness, the degree of hearing loss, and the shape of the audiogram. There was no significant difference in the total effective rate between the sudden deafness patients with tinnitus and those without (p > 0.05), indicating that the presence or absence of tinnitus had no significant influence on the prognosis, which was the same as the results of most scholars. In this study, the hearing effect of sudden deafness in the group with high frequency tinnitus (35%) was the lowest, and there was significant difference (p < 0.05), respectively, with the group of no tinnitus (73.4%) and low frequency tinnitus (85.4%). These differences suggest that hearing efficacy (total effective rate) is associated with the frequency of accompanying tinnitus at onset. Generally speaking, sudden deafness with tinnitus does not mean poor hearing prognosis, especially with low and intermediate frequency tinnitus. However, sudden deafness with high frequency tinnitus has the worst efficacy; the total effective rate of the sudden deafness with high frequency tinnitus is significantly lower than the group without tinnitus and with low frequency tinnitus. The reason may be that, according to the homeostatic model of tinnitus, the spontaneous discharge high frequency sound is perceived by patients, and the cochlear bottom hair cell damage is usually ineffective. Consistent with previous studies that high frequency tinnitus is usually a legacy symptom after the end of treatment and gradually developed into chronic tinnitus, indicating no further improvement in hearing. Study [Tanet al., 2013] showed that patients with chronic tinnitus tended to experience high frequency hearing loss. The difference between acute and chronic tinnitus may explain the different audiometric patterns, therefore, high frequency tinnitus has worse hearing efficacy.

There was no significant difference in the total effective rate between the two groups with different tinnitus loudness (p > 0.05). The results showed that the loudness of tinnitus was not significantly associated with sudden deafness prognosis. This is consistent with previous studies, where tinnitus severity assessed by THI is not a prognostic factor for hearing improvement [Nogueira-Neto et al., 2016].

In many studies [Pan et al., 2009; Sereda et al., 2011; Lee et al., 2015; Cvorovic et al., 2021], there was no association between tinnitus frequency and the shape of the audiogram. This study found statistical differences in the distribution of tinnitus frequency in different shapes of the audiogram. Table 5 shows that the low frequency descending audiogram is more accompanied by low frequency tinnitus (83.1%), the high frequency descending audiogram is more accompanied by high frequency (75.6%), and the flat descending audiogram of low, medium, and high frequency tinnitus is (36.7%, 16.7%, 46.7%). The tinnitus frequency in patients with sudden deafness was consistent with the frequency of hearing loss [Li et al., 2015], which indicated that the tinnitus frequency in sudden deafness was often the frequency of hearing loss. The most likely causes of sudden deafness are virus infection and blood circulation disorder in inner ear, which eventually leads to the loss of hearing caused by the damage of cochlear hair cells. The mechanism of morbidity tinnitus is not clear at present, and the spontaneous discharge of cochlear hair cells caused by ischemia in the inner ear is one of the possible morbidity mechanisms of tinnitus. Further detailed study of tinnitus in sudden deafness may shed light on the mechanism of tinnitus and may lead to the development of effective treatment for tinnitus. Low frequency descending type sudden deafness mostly accompanied by low frequency tinnitus, pathological changes of low frequency descending type sudden deafness mainly located in the cochlear top, the blood supply of cochlear top is good, the membranous labyrinth hydrops are easy to recover after treatment, the curative effect of sudden deafness with low frequency tinnitus is no different than that of the group without tinnitus. High frequency descending type sudden deafness mostly accompanied by high frequency tinnitus, pathological changes of high frequency descending type sudden deafness mainly located in the cochlear floor, the treatment of hair cell damage, and ion channel obstacle are usually ineffective and difficult to recover, so the hearing effect of sudden deafness with high frequency tinnitus is the worst, the total effective rate is obviously lower than that of the group without tinnitus and low frequency tinnitus.

As this study is retrospective, the relationship between characteristics of tinnitus and the hearing curative effective rate of sudden deafness is exploratory, and its causality needs to be further confirmed by a prospective study. There were many limitations with the small number of cases in the group with intermediate frequency tinnitus and the strong subjectivity of tinnitus matching. More research directions, such as better treatment methods, tinnitus sound type affects the hearing efficacy of sudden deafness, need further large sample study to provide multiple approaches for evaluating the hearing prognosis of sudden deafness.

In conclusion, whether tinnitus is present or not and different tinnitus loudness, there is no significant difference in the hearing effect of patients with sudden deafness, but the hearing effect of different tinnitus frequencies is significantly different. Patients with low and medium frequency tinnitus (125∼2,000 Hz) and no tinnitus have better hearing efficacy, and those with high frequency tinnitus (3,000∼8,000 Hz) have worse hearing efficacy. Therefore, test the tinnitus characteristics of patients in the initial stage of sudden deafness has certain guiding significance for the evaluation of hearing prognosis.

This retrospective research was carried out at E.N.T. Department of Tongde Hospital, Zhejiang Province according to the principles of the Declaration of Helsinki. The study has been granted an exemption from requiring written informed consent and approved by the Ethics Committee of Tongde Hospital, Zhejiang Province, and the approval No. is ZTDKSZ (2022) No. 083.

The authors have no conflicts of interest.

There was no funding for this study.

Ting Zou: guarantor of integrity of the entire study; Ting Zou and Jin Xu: study concepts, design, literature research, manuscript preparation, and editing; Ting Zou, Hongyi Lu, and Mingqiang Yu: material preparation, data collection, and analysis. All authors read and approved the manuscript.

All data generated or analyzed during this study are included in this article. Further inquiries can be forwarded to the corresponding author.