|Year : 2016 | Volume
| Issue : 4 | Page : 196-202
Impact of controlling hypothyroidism on auditory dysfunction
Naema Ismail1, Kandeel Hanaa2, Reda Behairy1, Asmaa Shoaeb3
1 Audiology Unit, Department of ENT, Al-Azhar University, Cairo, Egypt
2 Department of Endocrinology, Faculty of Medicine, Al-Azhar University, Cairo, Egypt
3 Department of Audiology, El Menshawy Hospital, Tanta, Egypt
|Date of Submission||12-Dec-2016|
|Date of Acceptance||20-Mar-2017|
|Date of Web Publication||23-Jun-2017|
Lecturer of Audiology, ENT Department, Al Azhar University for girls
Source of Support: None, Conflict of Interest: None
Background Hypothyroidism is defined as deficient thyroidal hormone production, and may be congenital or acquired.
Aim The aim of the study was to determine the presence of auditory disorder in a group of Egyptian women with hypothyroidism and to detect the effect of medical treatment of hypothyroidism on auditory function.
Patients and methods Forty hypothyroid women, their ages ranging from 30 to 60 years, were divided into two groups: group 1 (recently diagnosed group), which consisted of 20 drug-naive patients (this group was studied before and after treatment in the form of thyroid hormone replacement); and group 2, which consisted of 20 chronic patients out of medical control. All patients were submitted to history, full clinical examination, pure tone audiometry (PTA), immittancemetry, and auditory brainstem response.
Results Sensorineural hearing loss was found among the hypothyroid patients of bilateral mild to moderate hearing loss. Statistically insignificant improvement of PTA threshold was present in the recently diagnosed group after treatment. There was a statistically significant improvement in absolute latencies of waves III and V and interpeak latencies of I–III and I–V in the recently hypothyroid post-treatment group. There were insignificant correlations between the levels of free thyroxin 4 and thyroid-stimulating hormone and auditory changes in hypothyroid patients. There was a statistically significant (positive) correlation between thyroid peroxides antibody and PTA threshold at 250, 500, 4000, and 8000 Hz for all studied groups. However, there was a statistically insignificant (positive) correlation between thyroid peroxides antibody and changes in auditory brainstem response.
Conclusion The auditory changes in hypothyroid patients is reversible and may improve after treatment with thyroid replacement hormones (l-thyroxine).
Keywords: auditory brainstem response, hypothyroidism, pure tone audiometry
|How to cite this article:|
Ismail N, Hanaa K, Behairy R, Shoaeb A. Impact of controlling hypothyroidism on auditory dysfunction. Al-Azhar Assiut Med J 2016;14:196-202
|How to cite this URL:|
Ismail N, Hanaa K, Behairy R, Shoaeb A. Impact of controlling hypothyroidism on auditory dysfunction. Al-Azhar Assiut Med J [serial online] 2016 [cited 2020 Mar 31];14:196-202. Available from: http://www.azmj.eg.net/text.asp?2016/14/4/196/208933
| Introduction and rationale|| |
One of the most important dysfunctions of the thyroid gland is hypothyroidism in which the production of thyroid hormones is impaired, thus resulting in generalized reduction in metabolism of all systems. Hypothyroidism affects 2% of adult women and only 0.2% of men .
Hearing loss may be one of the most common otorhinolaryngological manifestation of acquired hypothyroidism. Auditory symptoms may happen alone or in association with vertigo and tinnitus . Meanwhile, hearing loss was reported with hypothyroidism and its pathology is not clearly understood yet. There are studies that have failed to detect a definitive relationship between hypothyroidism and hearing loss . In addition, the results of audiological evaluation of patients with hypothyroidism under treatment with l-thyroxine (LT) are conflicting. Thus, this study was designed to determine the presence of auditory disorder in a group of hypothyroid Egyptian women patients and to detect the effect of medical treatment of the hypothyroidism on auditory function.
| Patients and methods|| |
This study included 40 hypothyroid women, their ages ranging from 30 to 60 years, selected from the endocrine clinic of Al-Zahraa University Hospital. They were divided into two groups. Group 1, which included 20 drug-naive recently diagnosed hypothyroid patients (40 ears), was studied before treatment and restudied again when the patients became euthyroid by medical treatment in the form of thyroid hormone replacement (LT) for about 3 months. Group 2 included 20 chronic hypothyroid patients (40 ears) out of medical control because of poor compliance to medication, with the duration of their diagnosis ranging from 1 to 5 years. Ethical committee of El-Azhar University approved of protocol.
Following were the exclusion criteria: hypothyroidism due to iodine deficiency or thyroidectomy, history of otological diseases and ototoxic drugs, acoustic trauma and head trauma, ear surgery and perforated tympanic membrane, and history of hereditary hearing loss. Verbal and written consent was taken from all participants before starting the study.
All patients were submitted to the following: full medical history and clinical examination including anthropometric measurements as body weight, height, and waist circumference. BMI was calculated as weight in kilograms divided by squared height in meters (kg/m2). According to BMI, the participants were divided into normal and overweight groups (BMI<25 kg/m2) and the obese group (BMI>25 kg/m2) . Laboratory investigation was in the form of thyroid profile free thyroxin 4(FT4; normal range: 0.8–2.0 ng/dl), thyroid-stimulating hormone (TSH; normal range: 0.35–4.94 μIU/ml), and thyroid peroxidase antibody (TPO AB; normal range: <5.61 IU/ml). Full audiological history, otological examination, pure tone audiometry (PTA), speech audiometry using a pure tone audiometer (Ac40, Interacoustic, Denmark), immittancemetry using Miaco44 (German), and auditory brainstem response (ABR) (neurological assessment) using a Biologic Navigator PRO (German): three electrodes were used as follows: one frontal (Fz) electrode and another two electrodes were placed on the left and right mastoids. Click acoustic stimuli at rarefaction phase were delivered monaurally through an insert phone. Stimulus intensity of 90 dBnHL was used with repetition rate 21.1/s, whereas analysis time was 10.66 ms. Response sweeps of 1024 were used and band pass was filtered within 100–1500 Hz). Two traces were collected to ensure reproducibility. The response was identified by the presence of waves I, III, and V. The absolute latencies of waves I, III, and V and interpeak latencies were calculated in right and left ears.
The collected data were organized, tabulated, and statistically analyzed using statistical package for the social science (SPSS, version 16, Chigeco IL, USA). For qualitative data, comparison between two groups and more was done using the χ2-test. Post-hoc test was calculated for significant values after analysis of variance to determine which comparisons contributed to the significant values.
| Results|| |
A statistically significant difference was found in waves III and V latencies and I–III and I–V interpeak latencies among the studied groups at low repetition rate (LRR) ([Table 5]).
|Table 5 Comparison between the studied groups regarding mean±SD of body mass index and laboratory results (free thyroxin 4, thyroid-stimulating hormone, and thyroid peroxidase antibody)|
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A statistically significant difference was found between the studied groups as regards BMI ([Table 7]).
|Table 7 Correlation between body mass index and laboratory results (free thyroxin 4 and thyroid peroxidase antibody) and low repetition rate (absolute and interpeak latencies) of auditory brainstem response waves in recently diagnosed hypothyroid pretreatment group|
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Statistically significant (positive) correlation was found between TPO AB and PTA threshold at 250, 500, 4000, and 8000 Hz; there was statistically insignificant (positive) correlation between BMI, TSH, and PTA threshold; moreover, there was statistically insignificant (negative) correlation between FT4 and PTA threshold in the recently diagnosed hypothyroid pretreatment group ([Table 6]).
|Table 6 Correlation between body mass index and laboratory results (thyroid-stimulating hormone, free thyroxin 4 and thyroid peroxidase antibody) and pure tone audiometry threshold in recently diagnosed hypothyroid pretreatment group|
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Statistically insignificant (positive) correlation was found between BMI, TSH, and TPO AB and LRR (absolute and interpeak latencies) of ABR waves; there was statistically insignificant (negative) correlation between FT4 and LRR (absolute and interpeak latencies) of ABR waves in the recently diagnosed hypothyroid pretreatment group.
| Discussion|| |
Hypothyroidism is defined as a decrease in serum concentration of thyroid hormone that leads to increased secretion of TSH, resulting in elevated serum TSH concentrations. Hypothyroidism may be congenital or acquired. Acquired hypothyroidism is divided into primary, secondary, and tertiary hypothyroidism .
The current study included 40 women patients (20 of them recently diagnosed drug-naive hypothyroid women, with a mean age of 41.90±6.55 years, compared with 20 chronic hypothyroid patients out of medical control, with a mean age of 40.55±8.01 years. As regards age, there was no statistically significant difference between them (P>0.05).
This explains that the two groups were age matched to avoid the effect of senility on auditory function, and this also explains that hypothyroidism is more common in middle age than in old age and more common in females (2%) than in males (0.2%). This result was in agreement with the results obtained by Pearce et al.  and Karakus et al. .
In the current study, 75% of the recently diagnosed drug-naive group had positive TPO AB, which decreased to 60% after treatment. In chronic hypothyroid patients, there was 60% positive TPO AB. These results could be explained by the fact that autoimmune thyroiditis is a common cause of hypothyroidism. In addition, anti-TPO ABs are specific to Hashimoto’s thyroiditis, which is the commonest cause of autoimmune hypothyroidism. These results were in agreement with Trbojevic and Djurica 
In the current study, regarding PTA threshold, there was elevated PTA threshold in the recently diagnosed pretreatment hypothyroid group compared with recently diagnosed post-treatment and chronic hypothyroid groups, with no statistically significant differences ([Table 1]). This meant that there was an improvement in PTA threshold in recently diagnosed hypothyroid patients after return to euthyroid state by medical treatment (LT).
|Table 1 Comparison between the studied groups regarding mean±SD of pure tone audiometry threshold|
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The elevation in PTA threshold in recently diagnosed pretreatment and chronic hypothyroid groups could be explained by decreasing levels of thyroid hormone, mostly leading to decrease in cell energy production, that is, microcirculation, metabolism, and oxygenation of the inner ear structures . The improvement in hearing within the post-treatment group means that hypothyroidism has a temporary and reversible impact on hearing.
These results were in agreement with Zekiye et al.  who reported that physiological changes that occur in the inner ear in hypothyroidism might be reversible by treatment. These are also in agreement with Santos et al.  and Aggarwal et al.  who found high audiometric thresholds at all frequencies in hypothyroid female patients than in the control group. They also reported hearing improvement after thyroxin treatment. In the present study, studying the degree of hearing loss in hypothyroid patients revealed statistically significant differences among the studied groups as regards degree of hearing sensitivity ([Table 2]).
|Table 2 Comparison between the studied groups regarding degree of hearing sensitivity|
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This result was in agreement with the studies by Karakus et al. , Zekiye et al. , and Thornton and Jarvis  who found mild and moderate sensorineural hearing loss in their patients, and after an adequate substitution therapy with thyroid hormone, a definite improvement in hearing loss was found. The findings of the current study were in contrast to the study by Mra and Wax  who did not report any changes in hearing threshold in a group of hypothyroid patients by using PTA measurement. This could be explained by their small sample size. Moreover, both male and female patients were included in their study.
In the current study, regarding ABR, there was a statistically significant prolongation in absolute latencies of waves III and V and interpeak latencies of I–III and I–V in the recently diagnosed hypothyroid pretreatment group and in the chronic hypothyroid group compared with the recently diagnosed hypothyroid post-treatment group ([Table 3]). This indicates improvement of ABR wave latencies and interpeak latencies after thyroid hormone replacement therapy. This result could be explained by correction of thyroid hormone (FT4) level (1.50±0.22) in the recently hypothyroid post-treatment group, which leads to proper excitability of the peripheral and central auditory pathway, as explained by the results of Kowsalya et al. .
|Table 3 Comparison between all studied groups regarding mean±SD of absolute and interpeak latencies (ms) of auditory brainstem response waves at low repetition rate|
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These results were in agreement with Figueiredo et al.  who found a marked increase in absolute latencies of waves III and V, and interpeaks latencies I–III and I–V in hypothyroid patients. This was also in agreement with Santos et al.  who suggested that in hypothyroid state there may be some slow conduction at the periphery and with treatment; a significant improvement was shown in waves I and III.
The current study disagreed with Anand et al.  and Di Lorenzo et al. ; they observed an increase in wave V absolute latency and interpeaks latencies III–V and latencies I–V in patients with hypothyroidism, but these changes were maintained after hormonal replacement therapy. This result could be attributed to short duration of treatment and studying old age patients. Meanwhile, Ozata et al.  found no abnormalities in ABR in patients with hypothyroidism. This could be attributed to variation in recording procedure, sample size, and the extent of dysfunction.
In the current study, there was a highly statistically significant difference between the recently diagnosed pretreatment hypothyroid group and the recently diagnosed post-treatment hypothyroid group regarding BMI, as shown in
[Table 4] and [Table 5]. This means that there was an improvement in BMI after thyroid replacement therapy. BMI was statistically insignificantly (positive) correlated with PTA threshold at all frequencies ([Table 6]) and ABR parameters at LRR (absolute and interpeak latencies) ([Table 7]).
BMI was one of the risk factors to which hypothyroidism-related hearing loss was attributed in our study. This result was supported by the study carried out by Curhan et al.  who found that higher BMI and larger waist circumference were associated with increased risk for hearing loss. Mechanisms that may underlie the relation between obesity and hearing function include hypoxia and ischemic damage, oxidative stress, formation of reactive species, and resultant death of cochlear and spiral ganglion cells that leads to hearing loss.
The present study showed a highly statistically significant improvement in FT4 level and TSH after thyroxin replacement therapies, which reached normal levels in the recently diagnosed hypothyroid post-treatment group but not in the chronic group because of irregular use of treatment ([Table 5]).
FT4 level was insignificantly negatively correlated with PTA threshold and ABR parameters, whereas TSH level was insignificantly positively correlated with PTA threshold and ABR parameters ([Table 6] and [Table 7]). These results were in agreement with Ben-Tovim et al.  who reported that the changes seen in the PTA threshold and ABR are directly associated to the serum level of FT4. Meanwhile, Karakus et al.  could not find any statistically significant relation between the audiometric measurement and ABR results and an increase/decrease in FT4 or TSH levels.In the current study there was a statistically significant positive correlation between TPO AB and PTA threshold at 250, 500, 4000, and 8000 Hz for all studied groups ([Table 6]). Moreover, there was statistically insignificant positive correlation between TPO AB and LRR (absolute and interpeak latencies) of ABR waves of the study group ([Table 7]). This indicates that hypothyroidism is an autoimmune disease that leads to auditory system disorder by neuronal degeneration, endolymphatic edema, fibrous tissue proliferation, and atrophy of the organ of Corti .
| Conclusion|| |
Twenty-three percent of hypothyroid patients showed mild sensorineural hearing loss. The auditory changes in hypothyroid patients is reversible and may improve after treatment with thyroid replacement hormones (LT). Overall, 75% of the recently diagnosed drug-naive group had (positive) TPO AB, which decreased to 60% after treatment, indicating that autoimmune thyroiditis is a common cause of hypothyroidism.
Auditory evaluation and follow-up must be carried out whenever hypothyroidism is diagnosed. A combination of corticosteroid and hormonal replacement therapy should be considered for hypothyroid patients.
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Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]