Introduction
BERA is an electrophysiological test procedure which studies the electrical potential generated at various levels of auditory system starting from cochlea to cortex.1
There are a few pure tone and impedance audiometric tests designed to differentiate between cochlear and retrocochlear hearing loss, BERA is most accurate and sensitive for diagnosis of lesions in VIII nerve and auditory pathway in brainstem, especially in adults. BERA is a non-invasive and the most cost-effective method for diagnosing retrocochlear lesion.2
Approximately 1 of every 1000 children is born deaf. Early diagnosis of hearing impairment is important as the rehabilitative procedure can be started early which help speech and language development. It is impossible to perform pure tone audiometric tests on children but BERA provides rapid and efficient way to screen for deafness.
These tests can be divided into behavioural tests and objective tests. Behavioural tests are those, which require patient cooperation in regarding to a given stimulus. Objective tests do not require patient cooperation and provide recordable data in response to an acoustical stimulus.3 Brainstem evoked response audiometry (BERA) is most specific and sensitive test for brain stem dysfunction. It is most important objective method for evaluating peripheral auditory system in neonates, infants, sedated and comatose patients and other person who doesn’t understand the language.4
Due to the objective nature of the test auditory evoked potentials like ABR were introduced in screening children for hearing loss worldwide.5 This technique has difficulties in the determination of the participating frequency ranges because the test collects responses from the whole basement membrane with a stimulus tone of short duration. As a result, the ABR method has little frequency specificity. In addition, ABR tests conducted with click stimuli are of limited use in identifying threshold levels at low-frequency ranges.6 The ABR test is also has limitations in identifying characteristics of severe hearing loss over 90 dB HL because this range is beyond its detection limit.6
BERA is an objective study for assessing hearing loss on patients with inconsistent responses on pure tone audiogram. BERA helps to assist with detection of lesions like vestibular schwanommas, multiple sclerosis, stroke, trauma etc. BERA is a non invasive technique, easily recordable, not affected by sedation, anesthesia or age; hence the present study.
Materials and Methods
This study entitled “Brainstem evoked response audiometry (BERA) and its applications in ENT” was conducted in department of ENT, Vijayanagara institute of medical sciences, Bellary during June 2019 to December 2020.
Source of data
The patients attending the department of ENT and also patients referred from other departments of combined hospitals of MCH VIMS, Bellary form the subjects for our study in whom PTA or BERA can be done and are willing, during June 2019 to December 2020.
The evaluation is done in following stages
A written informed consent is taken from all patients included in the study. A detailed history-taking, thorough clinical examination done for these patients. The data collected is being entered into a specially designed case record form.
Pure tone audiometry (PTA)
The average hearing threshold is calculated by taking average of hearing threshold at 500, 1000, 2000 Hz.
BERA apparatus
Machine used for recording BERA was RMS EMG EP MARK-II machine manufactured by RMS RECORDERS and MEDICARE SYSTEM, Chandigarh. It is a computerized machine with facilities like- artifact rejection and common mode rejection
The room
The test was carried out in pre-cooled (temperature 21 degree centigrade) sound treated room. The electrical interference was kept minimal by spacing away the test room transformers, lifts etc. the room was spacious 10 feet by 10 feet with couch to lie down for patient.
Pre Test preparation
Each test carried out with prior appointment. Patient was subjected to ENT and pediatric examination prior to test. Patient was instructed to clean scalp with shampoo and not apply oil. Children given sedation syrup tricloryl as per dose recommended by pediatrician.
Preparation of patient
Patient was made to lie down on couch with head supported by pillow. Skin was prepared with surgical spirit. Electrode gel (Ten 20 conductive gel) was applied. Gel is non staining, non irritant to skin, sodium chloride free, water soluble.
Electrode placement
Silver electrodes were used and applied in following fashion:
Electric impedance is always kept less than 3K Ohms and difference between electrodes was not more than 1K Ohms.
The machine setting
Acoustically shielded TDH 32 earphones were used to cut down acoustic interference. Stimulus was given in the form of clicks at a rate of 11.3 per second. Each click duration was kept between 150 to 3000 Hz. Analysis time was 10 ms, 2000 responses were averaged.
In pediatric age group
The test was started after baby is asleep. The first stimulus was given at 125 dBnHL level (maximum intensity available) and decreased by 10 dBnHL for next run if wave V present. Both ears were tested separately. At each intensity run efforts were made to identify wave V. it was confirmed by re-run. Presence of peak V was taken as ability to hear. Each patient was categorized into normal, mild, moderate and severe hearing loss.
In adults
The test was started after the patient was lying still on couch and comfortable. First PTA thresholds for clicks were determined and better ear was tested. Then stimulus presented was
At 60 dB sensational level, whenever it was possible to give 60dB SL in both ears.
Otherwise when there was disparity in thresholds, the threshold for clicks for worse ear was found out using masking. Then considering the maximum limit of intensity available the sensational level was calculated and the test was carried out on both ears at this particular sensational level. Each ear was tested separately and masking was used in worse ear whenever required.
From BERA waveform thus obtained following calculations were made
Inter aural latency difference in I-V inter peak interval
I-V Inter peak interval
Inter aural difference in wave V latency
Absolute latency of wave V
Selective loss of late waves
Grossly degraded wave form morphology
Guidelines used to identify wave V are:
Appears after latency of 5 milliseconds (mean 5 7±0 25 ms
With decrease stimulus intensity its latency increases
Can be reproduced following re-run
Absence of peak in neutral run
We used normative values determined by Gupta and vishwakarma in Indian setup. 7, 8
The report of test was given in the format shown in proforma. Statistical test and Mc.Namara’s test was applied whenever applicable.
Results and Observations
The observations recorded in the study are described under following headings:
Pediatric age group
In our study pediatric age group ranged from 8 months to 168 months (14 years), mean age 66.61 months with standard deviation of 48.16 months. Most of the children were in the age group of 6 to 10 years.
In our study, in pediatric age group the number of male patients were 22 (61.1%) & female patients 14 (38.9%) with a male: female ratio of 3:2
The most common presenting complaint in our study in the pediatric age group was bilateral hard of hearing since birth.
Perinatal history
In our study maximum pediatric patients (36.1%) had normal perinatal history, apart from which post-meningitis (27.8%) was the most common perinatal history.
Absolute latency of V (ms)
The absolute latency of wave V was normal in 26 patients (72.2%) and abnormal in 10 patients (27.8%) in our study among the pediatric age group. The mean absolute latency of wave V is 5.76±0.39 ms in left and 5.75±0.41 ms in right ear.
Interaural difference in wave v latency (ms)
In our study the interaural difference in wave V latency was normal in most patients (83.3%) & abnormal in 16.7% in the pediatric age group.The mean interaural difference in wave V latency is 0.02±0.03 ms.
Interpeak latency I-V (ms) right ear
The interpeak latency I-V for the right ear was abnormal in 19 patients (52.8%) & normal in 17 patients (47.2%) in the pediatric age group in our study. The mean interpeak latency I-V for the right ear is 4±0.01 ms.
Interpeak latency I-V (ms) Left ear
The interpeak latency I-V for the left ear was abnormal in 19 patients (52.8%) & normal in 17 patients (47.2%) in the pediatric age group in our study. The mean the mean interpeak latency I-V for the left ear is 4±0.01 ms.
Interaural latency difference IN I-V Interpeak interval
In our study in the pediatric age group the interaural latency difference in I-V interpeak interval was abnormal in 19 patients (52.8%) & normal in 17 patients (47.2%). The mean interaural latency difference in I-V interpeak interval was 0.0094±0.0075.
Grossly degraded wave
In our study in the pediatric age group normal wave was seen in 16 patients (44.4%), only wave V was present in 13 patients (36.1%), wave V & III in 1 patient (2.8%) & no wave could be identified in 6 patients (16.7%).
Interpretation
Table 0
|
Interpretation |
Frequency |
Percent |
|
No wave identified |
6 |
16.7% |
|
Normal wave with normal latencies |
15 |
41.7% |
|
Only wave III and V identified |
1 |
2.8% |
|
Only wave v identifiedat 120 dB |
14 |
38.9% |
|
Total |
36 |
100.0% |
In our study in pediatric age group, 15 cases (41.7%) was interpreted normal wave with normal latencies after analysing all the values. Only wave V identified in 14 cases (38.9%) in children with profound hearing
Conclusion
Table 0
In our study in pediatric age group, 15 cases(41.7%) had normal hearing on screening, 13 cases(36.1%) had profound hearing loss without any risk factors, 6 cases(16.7%) had hearing loss due to meningitis complications, 2 cases(5.6%) had hearing loss due to neonatal jaundice.
Inference
Children with risk factors are 1.65 at more risk of developing hearing loss when compared to normal children; but statistically not significant.
Adults
In our study the mean adult age was 57.50 years with a standard deviation of 14.36, most patients belonged to age group >60years.In our study, in the adult age group the numbers of male patients were 8 (57.1%) & female patients were 6 (42.9%) with male predominance.
In our study in the adult patients the most common presenting complaint was hard of hearing present in all patients(100%), 2 cases(14.3%) had associated tinnitus and one case(7.1%) had associated tinnitus and giddiness.
PTA right ear
In our study in the adult patients PTA right ear showed moderately severe hearing loss in most (42.9%) patients followed by severe hearing loss (35.7%).The mean pure tone audiometry value on right side is 63.91±14.62 dB.
PTA left ear
In our study in the adult patients PTA left ear showed moderately severe hearing loss in most (42.9%) patients followed by moderate hearing loss (28.6%).The mean pure tone audiometry value on left side is 54.40±13.72 dB.
Absolute latency of V right ear (ms)
The absolute latency of wave V in the right ear was normal in 12 patients (85.7%) and abnormal in 2 patients (14.3%) in our study among the adult age group. The mean absolute latency of wave V in the right ear was 5.57±0.13 ms.
Absolute latency of V (ms) left ear
The absolute latency of wave V in the left ear was normal in 13 patients (92.9%) and abnormal in 1 patient (7.1%) in our study among the adult age group. The mean absolute latency of wave V in the left ear was 5.69±0.12 ms.
Interaural difference in wave V LATENCY (ms)
In our study the interaural difference in wave V latency was normal in most patients (78.6%) & abnormal in 21.4% in the adult age group. The mean interaural difference in wave V latency was 0.0182±0.0060 ms.
Interpeak latency I-V (ms) Right ear
The interpeak latency I-V for the right ear was normal in 12 patients (85.7%) & abnormal in 2 patients (14.3%) in the adult age group in our study. The mean interpeak latency I-V for the right ear was 4.0017±0.0103 ms.
Interpeak latency I-V (ms) left ear
The interpeak latency I-V for the left ear was normal in 13 patients (92.9%) & abnormal in 1 patient (7.1%) in the adult age group in our study. The mean interpeak latency I-V for the left ear was 4.02±0.0598 ms.
Interaural latency difference in I-V Interpeak interval
In our study in the adult age group interaural latency difference in I-V interpeak interval was normal in 11 patients (78.6%) & abnormal in 3 patients (21.4%).The mean interaural latency difference in I-V interpeak interval was 0.0091±0.0054 ms.
Conclusion
Table 0
Discussion
In our study in adults maximum patients had different severity of hearing loss 10 cases (70.1%), 2 cases had suspected retrocochlear pathology with history of hearing loss and tinnitus and absent waves apart from wave I suggesting lesion in auditory pathway. One case had above features plus giddiness suspicious of brainstem lesion/retrocochlear pathology. One case had normal hearing who had hearing loss on PTA with inconsistent responses suggesting of normal hearing/malingering.
In our study in pediatric age group 15 cases (41.7%) were found to have normal hearing, 13 cases(36.1%) had profound hearing loss since birth, 6 case (16.7%) had hearing loss post meningitis, 2 cases (5.6%) had hearing loss secondary to neonatal jaundice episode.
When compared to children who had risk factors with normal perinatal history children, Children with risk factors are 1.65 at more risk of developing hearing loss when compared to normal children; In a study conducted by Savić L, Milosević D.9 89 children evaluated and following risk factors was present: positive family anamnesis (deafness/severe hearing impairment) in 11 cases (12.3%). The other risk factors were found in 25(28.1%): preterm infants 12 (48%), hypoxia and asphyxia 6(24%), usage of the ototoxic drugs 3(12%), hyperbilirubinaemia 2 (8%), exsanguinotransfusion 1(4%), hydrocephalus 1(4%).
In our study hearing threshold was calculated by averaging hearing threshold at frequencies at 0.5, 1, 2 kHz. PTA could be done in our study on 14 patients and most had inconsistent responses for which BERA was done to measure the threshold objectively. Mean PTA threshold (in dB) in right ear was 63.91±14.62; in left ear 54.40±13.72. The degree of hearing loss according to WHO classification seen in our study are: right ear: mild 1 case (7.1%), moderate 2 cases (14.3%), moderate to severe 6 cases (42.9%), severe 5 cases (35.7%). Left ear: mild 3 cases (21.4%), moderate 4 cases (14.3%), moderate to severe 6 cases (42.9%) and severe 1 case (7.1%). Mean PTA threshold (in dB) in right ear was 63.91±14.62; in left ear 54.40±13.72. This is comparable to study conducted by Ghasias.10 mild hearing loss in 36 ears (60%), moderate 7 ears(11.6%), moderate to severe loss 6 ears (10%) and severe deafness in 11 ears (18.3%)
Absolute latency of wave V
In our study identification of wave V and measuring its absolute latency is a major criteria in diagnoses. It was measured separately for pediatric and adult group. In pediatric group the mean values (in ms) in right ear 5.75±0.41 and left ear 5.76±0.39. The values obtained on analyzing found normal in 10 cases (27.8%) and abnormal in 26 cases (72.2%).
In adult group mean value of absolute latency of wave V(in ms) in right ear was 5.67±0.13 and in left ea5.69±0.12. 12 cases (85.7%) were within normal limits on right and 2 cases were abnormal (14.3%). In left ear 13 cases (92.9%) were within normal limits and one case (7.1) had abnormal values. This was comparable with the study conducted by das, Manimay bandyopadhyay 11 on microcephalic children absolute latency of wave V(in ms) was 6.14±0.75 in test group and 5.1±0.25 in controls.
In a study done by Northern JL, Hayes D 12 Universal screening for infant hearing impairment, approximately 10% of all newborns are at risk for some type of developmental disability including hearing loss. Of these newborns at risk, 30% to 50% of every 1,000 have hearing impairments.
In adults 10 cases (70.1%) had hearing loss due to normal aging process, 2 cases (14.1%) had suspected retrocochlear pathology, one had suspected brainstem/retrocochlear lesion (7.1%) and one case (7.1%) was suspected malingering.
In our study in adults 2 cases had suspected retrocochlear pathology with history of hearing loss and tinnitus and absent waves apart from wave I suggesting lesion in auditory pathway. One case had above features plus giddiness suspicious of brainstem lesion/retrocochlear pathology. One case had normal hearing who had hearing loss on PTA with inconsistent responses suggesting of normal hearing/malingering.
Conclusion
In our study BERA was effective in identifying hearing loss thresholds by identifying wave V and its threshold and assessing auditory pathway in infants and children’s depending on the wave latencies. BERA along with Otoacoustic emissions can be used for newborn hearing screening.
BERA helps in predicting hearing loss where PTA shows inconsistent responses and also helps in identifying malingerers as BERA is an objective test.
BERA can be used to screen retrocochlear pathologies as seen in our study. Patients with hearing loss with tinnitus and giddiness screened and BERA performed had grossly degraded wave with identification of only wave I and absence of other waves and increased latencies and interaural difference in wave latencies suggests lesion in the auditory pathway. Depending on the absence of specific wave site of the lesion can also be made out. In our study 3 cases of retrocochlear pathology previously confirmed by MRI was taken and BERA was performed showing presence of only wave I and absence of remaining waves. BERA is screening test and should be confirmed by MRI.
Summary
This study was undertaken with the objective of evaluating the role of brainstem evoked response audiometry(BERA) and its applications in ENT in a setup like our hospital where screening of hearing in children, initial test to screen retocochlear pathologies, predict hearing thresholds can be done.
Fifty cases i.e. 100 ears were evaluated and BERA was performed on them after taking consent and after ENT examination. Values obtained were interpreted and results were given, statistics evaluation done and compared to other similar studies.
BERA is the accurate and reliable estimation of hearing levels in infants and young children and helps in early identification of hearing impairment and rehabilitative measures can be taken. In our study BERA was effective in identifying hearing loss thresholds and assessing auditory pathway in infants and children’s in whom behavioral methods and PTA evaluation is not possible and in children with significant perinatal history with risk of developing hearing loss. BERA is non invasive, easy to perform and interpret and cost effective screening test to assess hearing loss in infants and children which can be done in any OPD settings.
BERA is the accurate and reliable method for prediction of hearing loss in adults. It helps in predicting hearing loss where PTA shows inconsistent responses and also helps in identifying malingerers as BERA is an objective test.
BERA helps in evaluating cases of retrocochlear pathology/brainstem lesions. With history of hard of hearing with tinnitus/giddiness and SNHL on PTA, further evaluating with BERA, loss of waves or waves with increased latencies and interaural latency differences suggest retrocochlear pathologies. It is an effective screening test to diagnose retrocochlear pathologies which further has to be confirmed by MRI.
Though time consuming BERA is a non invasive, objective test in identifying hearing loss in infants and children, estimating hearing thresholds in uncooperative patients and as a screening test to diagnose retrocochlear pathologies and should be used as a part of routine audiometric test battery along with other tests to confirm and diagnose accurately.
