Study of auditory brainstem evoked response at varying frequencies in subclinical hypothyroid subjects
Indira Jha1, Kabir Alam1, Kaushal K Keshari1, Niska Sinha2, Tarun Kumar1
1 Department of Physiology, IGIMS, Patna, Bihar, India
2 Department of Psychiatry, IGIMS, Patna, Bihar, India
|Date of Submission||07-Dec-2022|
|Date of Acceptance||10-Feb-2023|
|Date of Web Publication||20-Jul-2023|
Dr. Niska Sinha
Department of Psychiatry, IGIMS, Patna - 800 014, Bihar
Source of Support: None, Conflict of Interest: None
Background: Hearing deterioration in hypothyroid subject was documented by Kemp. Cristiane et al. reported delayed waves latency in subclinical hypothyroid subjects. Recording of auditory brain stem evoked response in subclinical hypothyroid subjects at 80 dB and varying frequencies has been done.
Materials and Methods: Case control study. Group 1, N = 30 control subjects, free T3, free T4, thyroid stimulating hormone (TSH) within normal range. Group 2, N = 30 subclinical hypothyroid subjects, TSH was between 4.6-8 microIU/L. Student Unpaired t test was done. Those on epileptic, neuroleptics, depression, psychosis drugs, inflammatory, proliferative, traumatic ear disorder, smokers, on tobacco, COVID-19 positive subjects, altered sensorium, drug abuse, diabetes mellitus, neuropathy, hypertension, cardiac arrhythmia, family history of hearing disorder, and furosemide drug were excluded. Auditory brainstem evoked response (ABER) done.
Results: Mean ± SD of Brainstem evoked response auditory (BERA) waves III, V, interpeak latencies at 80 dB, 2, 4,6 KHz reported delay and significant in subclinical hypothyroid group as compared to control.
Conclusion: BERA study at 6 KHz and 80 dB detects central neuropathy earlier in subclinical hypothyroid patients.
Keywords: Brainstem auditory evoked potential, hearing impairment, subclinical hypothyroid, thyroid stimulating hormone
|How to cite this article:|
Jha I, Alam K, Keshari KK, Sinha N, Kumar T. Study of auditory brainstem evoked response at varying frequencies in subclinical hypothyroid subjects. Adv Biomed Res 2023;12:182
|How to cite this URL:|
Jha I, Alam K, Keshari KK, Sinha N, Kumar T. Study of auditory brainstem evoked response at varying frequencies in subclinical hypothyroid subjects. Adv Biomed Res [serial online] 2023 [cited 2023 Sep 28];12:182. Available from: https://www.advbiores.net/text.asp?2023/12/1/182/382073
| Introduction|| |
Hearing deterioration in hypothyroid subjects was documented by Kemp. Audiometrically, it was first documented by Hilger. Ozata et al. did not find any alteration in auditory brainstem evoked response in subclinical hypothyroid subjects. The hearing deterioration may be sensorineural, conductive, or both. The subclinical hypothyroidism has mild increase in TSH (4.6-8.0 mIU/mL) along with free T4 within normal range. These findings may be accompanied by mood swings, fatigue, and weight gain.
Brainstem auditory evoked potential (BAEP) is a non-invasive electrophysiological test which records the auditory pathway potentials from the ear to the brainstem. It detects deterioration of auditory pathway early. This study plans to record auditory brainstem evoked response (ABER) in subclinical hypothyroid subjects at varying frequencies of 2 KHz, 4 KHz, 6 KHz, and 80 dB. Relation of BAEP with antibodies of thyroid and central neuropathy has been done.
| Material and Methods|| |
Institutional Ethical Committee approval procedure was taken. Every participant gave the consent. A case control study started in December 2021 till November 2022 in the Dept of Physiology, IGIMS, Patna.
Subclinical hypothyroid subjects between 20 and 50 years of either sex were selected in the Department of Medicine IGIMS, Patna.
Group 1, N = 30 subjects with TSH less than 4.6 microIU/L and the age between 20 and 50 years were enrolled as control group.
Group 2, N = 30 subclinical hypothyroid patients with TSH between 4.6 and 8 microIU/L and age between 20 and 50 years were enrolled as cases. Subjects with increase TSH, Free T3, and Free T4 within normal range were selected. TSH, Free T3, T4 level, antibodies against thyroglobulin, and thyroid peroxidase were detected by Electrochemiluminescence assay.
It was hypothesized that ABER waves latency and interpeak intervals would be prolonged in subjects of subclinical hypothyroidism. Size of sample calculated by AI-therapy statistics BETA the large effect size taken was (0.8). The alpha value considered was 0.05. Power considered here was 80% for one tailed hypothesis. Subjects needed were 52 (26 in each group).
The patients taking drugs for psychosis, depression, epilepsies, and neuroleptics are excluded. Smokers, COVID-19 positive subjects, altered sensorium, and drug abuse were excluded. Patients with diabetes mellitus, chronic illness, family history of deafness, intake of ototoxic drugs, occupational history of loud noise, and ear disease or infection were excluded. For hearing loss Rennie's and Webbers tests were done.
Weight of body is measured in kilograms with the help of portable weighing machine. Height of body measured in centimeters. Subjects stood with their head, heels, and buttocks against a wall. Height was measured by an object placed on subject's head on a tape measure fixed to wall. BMI calculated as weight of body in kilogram divided by the body height in square meters (kg/m2).
On the electrodes recesses the standard adhesive paste applied for better conduction. Electrodes adhered to mastoid surfaces. The headphone kept in position. Filter set at 100Hz–3000Hz. Each ear stimulus was of short duration. Impedance kept low. BERA waves recorded at 80 dB and 2, 4, 6 KHz frequency. Two readings were recorded to confirm the reproducibility of BERA waves and interpeak latencies.
GRAPHPAD QUICKCALCS online student unpaired t test calculated the result. Mean and standard deviation of the parameters like BERA waves and interpeak latencies were compared between control and subclinical hypothyroid groups. The statistical significance was at P value < 0.05. Statistical highly significant was at P value < 0.001.
| Results|| |
ABER waves were compared between control and subclinical hypothyroid group 2 subjects.
Mean waves I, III, V and inter-peak I-III, III-V, I-V latency of group 1 at 80 dB, 2 KHz reported 1.60 ± 0.20, 3.52 ± 0.15, 5.43 ± 0.17, 1.78 ± 0.23, 1.93 ± 0.23, 3.78 ± 0.34, and group 2 reported 1.62 ± 0.21, 3.65 ± 0.15, 5.60 ± 0.31, 2.00 ± 0.26, 2.04 ± 0.18, 3.98 ± 0.41(ms), respectively. Mean of subclinical hypothyroid group reported statistical significant (P value < 0.05) except wave I reported non-significance (P value > 0.05). Wave III and I-III interpeak reported high significance (P value < 0.001) [Table 1] and [Figure 1].
|Table 1: Absolute latencies and inter peak latencies comparison in control group and subclinical hypothyroid group patients at 2 KHz and 80 dB|
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|Figure 1: Graphs at 2, 4, 6 KHz and 80 dBs in subclinical hypothyroid and control group|
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Mean of wave I, III, V and inter-peak I-III, III-V, I-V latency of group 1 at 80 dB, 4 KHz reported 1.62 ± 0.21, 3.53 ± 0.17, 5.44 ± 0.25, 1.81 ± 0.17, 1.94 ± 0.28, 3.80 ± 0.38 while group 2 reported 1.71 ± 0.2, 3.66 ± 0.2, 5.71 ± 0.37, 2.01 ± 0.27, 2.07 ± 0.21, 4.07 ± 0.37 (ms), respectively. Mean reported statistical high significance (P value < 0.001) in subclinical group except wave I reported non-significance (P value > 0.05), wave III-V significant in subclinical (P value < 0.05) [Table 2] and [Figure 1].
|Table 2: Absolute latencies and inter peak latencies comparison in control and subclinical hypothyroid group patients at 4 KHz and 80 dB|
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Mean of wave I, III, V and inter-peak I-III, III-V, I-V latency of group 1 at 80 dB, 6 KHz reported 1.62 ± 0.21, 3.54 ± 0.17, 5.45 ± 0.25, 1.82 ± 0.17, 1.96 ± 0.28, 3.81 ± 0.38 and group 2 reported 1.71 ± 0.2, 3.69 ± 0.2, 5.72 ± 0.37, 2.05 ± 0.27, 2.09 ± 0.21, 4.10 ± 0.37 (ms), respectively. Mean were statistically high significant (P value < 0.001) in subclinical group except wave I which was not significant (P-value > 0.05), wave III-V was significant (P value < 0.05) [Table 3] and [Figure 1].
|Table 3: Relationship between auditory brainstem evoked potential in subclinical hypothyroid group at 80 dB and 6 KHz|
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| Discussion|| |
ABER recorded and comparison done between subclinical hypothyroid and control group.
Wave I latency was reported non-significant. So, 8th nerve transmission till cochlear nucleus was normal. At 2 KHz, delay in absolute latency of wave III and wave V were highly significant and significant in subclinical hypothyroid group, respectively. Sangeeta et al. supported it. Ozata et al. did not support it. At 4 KHz delay in absolute latency of waves III and V and interpeak latency of wave I-III and I-V reported high significance, interpeak III-V reported significant delay in subclinical group. Cristiane et al. reported similar result. At 6 KHz delay in absolute latency of waves III, V and interpeak latency I-III, III-V and I-V reported high significance (P <.001) in subclinical hypothyroid group. Cristiane et al. supported it.
The percentage of subclinical hypothyroid subjects at 2 KHz, 4 KHz, and 6 KHz with delayed absolute latency of BERA waves III and V and all interpeak latency were 66.66% (20/30), 70% (21/30), and 80% (24/30), respectively. Increase in frequency of stimulus from 2 KHz, 4 KHz to 6 KHz led to recording of delayed BAEP easily. This is supported by Gupta V et al. In acquired hypothyroid patients, sensorineural hearing loss at higher frequency has been reported without affecting lower frequencies. Significant delay in the absolute latency (AL) of BERA waves III, V, and interpeak latency has been found in subclinical hypothyroid group. It targets auditory pathway at brainstem and midbrain. At 6 KHz, highly significant BERA waves reported in subclinical hypothyroid as compared to control by chi square test [Table 4]. They had normal tuning fork tests and no hearing related complaint. So, subclinical involvement as well as severity can be detected early by BERA test at 6 KHz.
|Table 4: Delayed auditory brainstem evoked potential in subclinical hypothyroid patients and control group at 6 KHz and 80 dB|
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The central nervous system (CNS) is deteriorated in subclinical hypothyroidism. Subclinical hypothyroidism leads to overt hypothyroidism. The most important cause of hypothyroidism is autoimmunity. Elevated levels of antibodies against thyroid peroxidase and thyroglobulin were reported in 60% subclinical hypothyroid subjects. Pathophysiology in hypothyroidism may be degeneration of cochlear hair cells which deteriorates potentials of cochlea. It affects protein synthesis, myelin production, and action of enzymes. T4 acts as a neurotransmitter in CNS. Hypothyroidism leads to lipid peroxidation, which generates free radical and causes tissue damage. Hashimoto's disease is the most common etiology of primary hypothyroidism where antibodies destroy thyroid gland or lymphocytes attack gland. Subjects with elevated serum TSH concentration with normal serum free thyroxine confirms hypothyroidism of subclinical type.
| Conclusion|| |
BERA investigation at higher frequency, i.e., 6 KHz and 80 dB detects central neuropathy earlier in patients of subclinical hypothyroid having no hearing complaint. Earlier detection of hearing pathway defect and intervention with thyroxine treatment may prevent disease progression and morbidity in subclinical hypothyroid patients.
Financial support and sponsorship
All the expenses borne by Principal Investigator Dr.Indira Jha.
Sponsorship - Nil.
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4]