Pure-tone audiometry and auditory brainstem responses in noise-induced deafness

Pure-Tone Audiometry and Auditory Brainstem Responses in Noise-Induced Deafness Ismail Noorhassim,

MD, Kimitaka

Kaga, MD, and Kousuke Nishimura

Purpose: The objective of this study is to find the relationship between pure-tone audiometry results and the auditory brainstem response wave abnormalities. Subjects and Methods: The pure-tone audiometry (PTA) and auditory brainstem responses (ABRs) from 22 patients (44 ears) with diagnosed noise-induced permanent hearing loss were studied. Three indices of PTAwere average thresholds of 0.5 kHz/, /l kHz, and 2 kHz (PTAl); 2 kHz and 4 kHz (PTA2); and 4 kHz (PTA3) were subdivided into 3 thresholds of hearing. Their relationships with ABR results were analysed. The patterns of PTAfrom various groups of ABR wave patterns were studied. Results: In this study, the abnormal ABR wave patterns were detected in 72.7% of the ears. The ears with prolonged ABR wave latency, absent early waves, prolong interpeak wave I-V latency was 20.5%, 18.2%, and 21 .l%, respectively. Normal ABRs were recorded in 27.3% of the ears despite marked thresholds elevation of the PTA at high frequencies. Other relationships between PTA results and ABR wave results were discussed. Conclusion: There were relationships between severity of noise-induced hearing loss indicated by PTA and the patterns of ABR wave abnormalities among workers with noise-induced permanent hearing loss. Copyright 0 1996 by W.B. Saunders Company.

The noise-induced hearing loss (NIHL) is one of the more common occupational diseases.’ Workers who are chronically exposed to noise levels greater than 85 dB(A) have a high risk of developing NIHL.2 Because this disease is compensable in many countries, including Malaysia, Japan, and United States of America, an objective investigation, eg ABR test, is sometimes needed to ensure that the workers’ claims are genuine. A study done by Suzuki et al has shown a good correlation between pure-tone audiometry (PTA) threshold and the auditory brainstem response (ABR) thresholds. The ABR thresholds are always higher than PTA thresholds by as much as 20 dB.3 Another study by Jerger and Mauldin has predicted that the average PTA thresholds of 1 kHz, 2 kHz, and 4 kHz of the subjects would be 40% lower than the ABR threshold. Many studies have reported the relationships between PTA and ABR waves patterns of sensorineural hearing loss. However, very few reports have examined the relationship between PTA and ABR for workers with noiseinduced permanent hearing loss. A study by G Almadori et al5 on 108 ears of NIHL patients has reported the latency values American

Journal

of Otolaryngology,

of wave I, wave III, and wave V, as well as interpeak wave intervals of III-I. V-I and V-I were within normal limits. They reported 10 ears (9.2%) with no wave I, 2 cases with both waves I and III absent, and 5 cases (4.6%) with an abscence of ABR waves. However, no clear relationships between the mean threshold of 1 kHz, 2 kHz, and 4 kHz of PTA and abnormal ABR waves were noted in the study. Attias and ProtF studied 31 workers who were working in noisy environment. They found that after having exposed to noise for more than 14 months, the ABR wave latency and interpeak wave intervals were prolonged between 0.2 ms to 0.3 ms and 0.1 ms to 0.5 ms, respectively, compared with results of ABR waves before they were exposed to the noise. From

the

Department

of

Community

Health,

Medical

Faculty, National University of Malaysia, Kuala Lumpur, Malaysia; the Department of Otolaryngology, University Tokyo Faculty of Medicine, Tokyo, Japan; and the President of Nishimula Hospital, Tokyo, Japan. Address reprint requests to lsmail Noorhassim, MD, De-

partment of Community

Health, Medical Faculty, National

University of Malaysia, Jalan Raja Muda, 50300 Kuala Lumpur, Malaysia. This study was sponsored in part by Japan Society Promotion of Sciences. Copyright 0 1996 by W.B. Saunders Company 0196-0709/96/l 701-0006$5.00/0

Vol 17, No 1 (January-February),

1996:

pp 31-35

31

32

NOORHASSIM,

The objective of this study is to find the relationship between threshold levels and the pattern of PTA results and ABR wave results from workers with permanent NIHL. SUBJECTS

AND METHODS

The subjects in this series were comprised of 22 men who worked in noisy environments, where the noise level was above 90 dB(A). There were 4 workers who were exposed to noise for 10 years or less; 7 workers who were exposed to noise between 11 and 20 years; and 11 workers who were exposed

AND

NISHIMURA

latency, prolonged interpeak wave I-V interval, early ABRs waves absent, and all ABRs waves absent (Fig 1). Three indices were computed from PTA. They were: PTA1 with the average threshold of 0.5 kHz, 1 kHz, and 2 kHz; PTA2 with the average threshold of 2 kHz and 4 kHz; and PTA3 with the threshold at 4 kHz. Each of the indices was subdivided into different levels of thresholds. The number of ears with abnormal ABR waves for the different threshold levels of PTA indices were analysed. The data were analysed using personal computer and descriptive analyses of studied variables will be reported in this article.

20 years or more. Mean and standard deviation of exposure were 21 2 12.7 years.

RESULTS

The patients’ age distributions were: 2 patients aged less than 50 years old, 5 patients aged between 50 to 59 years old, 11 patients aged 60 to 69 years old, and 4 patients aged 70 years old or more. The mean and standard deviation of age were 62.1 ? 9.9 years. The patients attended the otolaryngology clinic for assessment of NIHL. They were referred by their former factory doctors. No outer and middle ear problems were detected in these patients during the examination. The air conduction and bone conduction test of PTA were performed on all the patients. The test were carried out in a sound attenuated room. The audiometer were calibrated, and the threshold level of hearing for the frequencies of 125, 250, 500, 1000, 2000, 4000, 6000 and 8000 Hz were tested. The PTA results showed that all the subjects had having permanent NIHL disease. The ABR test was conducted in an electrically shielded, sound-attenuated room. Each patient was tested in a supine position, and the subject usually slept in the dimly lit test room. Data were recorded with silver disc electrodes from the forehead refer-

Abnormal

ABR Waves

Of the 44 ABR results that were analysed, 32 ears (72.7%) were found to be abnormal. The I

II

JJI

IV

v

A

B

enced to the test ear mastoid. The electrode at the opposite ear was grounded. The auditory stimuli were clicks (one cycle of a 3 kHz sine wave) produced by a signal generator (Dana Japan DA502) and delivered through TDH 39 earphones. Clicks were delivered at a rate of 10 clicks per second. The instensity of the stimuli were given from a hearing level (HL) of 90 dB up to 100 dB. Each ear was tested seperately. Two replicated waves were recorded for each ear to ensure the reliability of the test. Data of ABRs were differentially amplified through high-pass filter at 100 Hz and low-pass filter of 2 kHz. The amplified data were averaged and displayed by an on-line computer and graphically recorded with an X-Y plotter. The ABR wave latency and interpeak wave interval were considered to be abnormal when any of the waves were longer than 1.7, 2.9, 3.9, 5.1, 6.1, 2.5, 4.5, and 2.0 ms for wave I, II, III, IV, V, I-III, I-V and III-V respectively.7 Waves II and IV were not analysed in this study because they did not appear consistently in normal ABR waves. The types of ABR waves include: normal, prolonged ABR wave

KAGA,

C

D

7E CF

Fig 1. Types of ABR wave abnormalities. (A) Normal ABR waves; (B) Prolonged ABR wave latency; (C) Prolonged interpeak waves I-V interval; (D and E) Absence of early ABR waves; (F) All ABR waves absent.

PTA AND

ABR

IN NOISE-INDUCED

TABLE 1.

Ears

with Abnormal

DEAFNESS

33

ABR Waves ABR

Ears

(N = 44)

Prolonged waves Absent waves

I No. (%)

III No. (%)

I & III No. (%)

V No. (%)

I-V No. (%)

III-V No. (%)

8 (18.2) 8 (18.2)

15 (34.1) -

NA 3 (6.8)

8 (18.2) -

10 (22.7) -

12 (27.3) -

*Most of the ears have more than Abbreviation: NA, not applicable.

1 abnormal

ABRs

waves.

abnormality of ABRs were as follows: 8 ears (18.2%) with prolonged wave I latency, 8 ears (18.2%) with the absent wave I, and 10 ears (2.7%) with prolonged interpeak waves I-V interval. A total absence of ABR waves was not detected in any of the ears (Table I). Most of the ears had more than one ABR wave abnormality, eg 60% of those ears with prolonged interpeak wave I-V interval, also have prolonged interpeak waves III-V. In addition, 12 ears (27.3%) were found to be normal despite an elevated threshold of the PTA at high frequencies. The Relationship ABR Patterns

Between

PTA Indices

each group was 62.5% in group I, 15.4% in group II, and 30% in group III. The data from these groups showed many normal ABRs despite the markedly abnormal audiogram results. The PTA3 was divided into 3 groups. Group 1 (less than 60 dB) was made up of 13 ears, group II (60-69 dB) with 19 ears, and group III (70 dB and above) with 12 ears. The abnormal ABR waves noted for this indicator was 46.2% in group I, 79.0% in group II, and 92.3% in group III. Even at very marked elevation of threshold of hearing at 4 kHz level, normal ABRs were observed in 54.4% in group I, 21% in group II, and 7.7% in group III. The mean and standard deviation for each PTAl, PTA2, and PTA3 were computed for all ears with normal, prolonged ABR wave latency, prolonged interpeak wave I-V interval, and early wave absence, respectively. The highest mean threshold from among the three indicators was found in the group with absent wave I (Table II).

and

The threshold of PTA1 was divided into 3 groups. Group I (less than 25 dB) was made up of 14 ears, group II (25-34 dB) with 21 ears, and group III (more than 34 dB) with 9 ears. The abnormal ABR waves found in each group was 57% in group I, 71.4% in group II, and 100% in group III. However, among those with hearing impairment (threshold level of 25 dB and above), 19.4% were found to be normal ABRs waves in group II. The threshold of PTA2 was also divided into 3 groups. Group I (less than 40 dB) was made up 8 ears, group II (40-59 dB) with 26 ears, and group III (more than 59 dB) with 10 ears. The abnormal ABR waves noted for each group was 37.5% in group I, 84.6% in group II, and 70% in group III. The normal ABR waves for TABLE 2.

The Mean

Waves*

Threshold

PTA Indices

for Various

ABR

The Relationships Between Patterns and PTA Patterns

The mean threshold for each frequency of PTA from each group of normal ABRs, prolonged ABRs waves latency, prolong interpeak wave V-I, and absent early waves were calculated seperately, and the audiogram for each group was plotted (Fig 2). The audiograms indicated that the group Waves ABR

Normal PTA1 PTA2 PTA3

(x 2 sd) Hz (x 2 sd) Hz (x 2 sd) Hz

23.1 44.1 54.2

2 11.4 + 14.8 + 12.6

the ABR

Prolonged Waves 27.8 55.1 66.3

-e 5.9 -c 9.6 2 9.2

Waves Prolonged I-V Internal 30.2 51.3 60.0

k 8.4 + 15.9 + 14.1

Absent Early Waves 49.0 72.8 65.6

t 21 .l t 15.0 t 20.3

NOORHASSIM,

34

with an absence of early waves has the most severe hearing loss, whereby all their hearing frequencies were affected by noise. At high frequencies, the hearing was severely affected. The group of ears with abnormal interpeak, waves I-V were less severely affected as shown by the audiogram, although all their frequencies (except 125 Hz and 500 Hz) were abnormal, For those ears with normal ABRs waves, their audiograms were the least affected by noise. DISCUSSION Many studies have shown that noise exposure can cause degeneration to the sensory cell, especially the outer cells in the cochlea.8 The degeneration of other sites was also reported, including the primary cochlear nerve endings and synapses, the secondary neurons of the posterior caudal part of the ventral cochlear nucleus, and the octopus cell area of the ventral cochlear nucleus was also reported.g Other animal studies have shown that noise can induce degeneration of the auditory pathway ascending to the superior olivary complex and inferior colliculus.lo In this series, various ABR wave pattern abnormalities were detected (Table 1). The prolonged ABR wave I latency and prolonged interpeak wave I-V interval were detected among the permanent NIHL patients. These abnormalities suggested the possibility of degeneration of both the peripheral end organs and central auditory pathways. This is pos-

is‘D ‘”2-540

j

60

80

0

125

250

500

1000

Frequency

2000

4000

8000

Hz

(Hz)

group of ears with various types of Fig 2. Audiogram normal ABRs; +-+, prolonged ABR wave results (-., ABR wave latency; *-*, prolonged interpeak waves I-V; W-m, early ABR waves absent).

KAGA,

AND

NISHIMURA

sible because all the patients in this group had history of chronic exposure (min Z! SD = 21 2 12.7 years) to high levels of noise. Furthermore, each audiogram from the subjects with the prolonged interpeak wave I-V has C5 dip pattern, and the group mean threshold audiogram (Fig 2) showed the presence of a notch at 4000 kHz. For the presbycusis, their audiograms are usually without C5 dip pattern. However, considering the age of the patients in this group (60 + 8.7 years), the possibility that the abnormality was caused by the combination of permanent NIHL and presbycusis could not be excluded. The PTA1 and its relation to ABR wave abnormality is studied in this review, because the PTA1 is widely used in the assessment of workers who suffer from NIHL. It is used to assess the level of hearing impairment and percentage of hearing handicap of the workers.ll Since 1971, the hearing threshold at 3000 Hz was included in the calculation of PTAl. At the PTA1 threshold level of less than 25 dB, 57% of the ears showed abnormal ABRs waves. According to the definition of hearing impairment, I1 hearing is considered not impaired at this level. Therefore by using the ABR, we will be able to detect workers with early hearing loss and early preventive measures can be instituted for these workers and their workplace. At PTAl, threshold of 35 dB and above, all the workers had abnormal ABR test results. The PTA2 average threshold of 2 kHz and 4 kHz was analysed because the click ABR is mostly generated by cochlea activity above 1000 Hz, especially at 2000 Hz to 40 000 Hz range.12 Of the abnormal ABRs, 85% were detected in this series when the PTA2 threshold was at 40 dB or above. The PTA3 was studied because Jerger and Mauldin’s study has shown that PTA3 has the best coefficient correlation (0.49) and the best slope regression equation (0.63) with ABRs threshold as compared to other 6 PTA indices studied.4 Our study has shown that almost all workers have abnormal ABR test results in a PTA3 threshold of 60 dB or more. From the mean threshold of PTAl, PTA2, and PTA3 for various group of ABR waves results (Table 2), it can be shown that the ears with normal ABR wave results have the lowest

PTA AND

ABR

IN NOISE-INDUCED

DEAFNESS

threshold level and the group with early ABR absence has the highest threshold level. These patterns could be explained by severity of the degeneration of auditory system. Normal ABR patterns can be caused by recruit phenomena at cochlear level. From Figure 2, we can predict the type of ABR wave patterns based on the PTA pattern and its severity. Based on that audiogram, it is most likely that the ABR wave abnormalities start with prolonged wave latency, prolonged interpeak wave intervals, and absent waves followed by complete absence of the ABR waves. We have seen that each group of abnormal ABR waves has different audiogram pattern (Fig 2). A firm conclusion about the relationship of ABR abnormalities and PTA patterns could be made with a bigger sample size.

ACKNOWLEDGMENT Dr Noorhassim was sponsored by Japan Society Promotion of Sciences (JSPS)to have his scientific study at Department of Otolaryngology, University of Tokyo, Faculty of Medicine, Tokyo, Japan. Dr Kimitaka Kaga, the professor and chairman of that department who supervised Dr Noorhassim, allowed him to use his patients’ records for the case review.

35

REFERENCES 1. McCunney RJ: Occupational exposure to noise, in Rom WN (ed): Environmental and Occupational Medicine, (ed 2), Boston, MA, Little, Brown, 1992, pp 11211132 2. Hearing impairment caused by noise, in WHO Expert: Early Detection of Occupational Diseases, Geneva, Switzerland, World Health Organization, 1986, pp 165169 3. Suzuki T, Kodera K, Kaga K: Auditory evoked brainstem response assessment in otolaryngology. Ann N Y Acad Sci 388:480-500,198Z 4. Jerger J, Mauldin L: Prediction of sensorineural hearing level from the brainstem evoked response. Arch Otolaryngol104:456-461,1978 5. Almadori G, Ottaviani F, Paludetti G, et al: Auditory brainstem responses in noise-induced permanent hearing loss. Audiology 27:36-41, 1988 6. Attias J, Pratt H: Auditory evoked potentials and audiological follow up of subjects developing noiseinduced permanent threshold shift. Audiology 23:498508,1984 7. Kaga K, Shindo M, Tanaka Y: Auditory brainstem responses and nonsense monosyllable perception testing finding for patient with nerve and brainstem lesions. Laryngoscope 96:1272-1278,1986 8. Lim DJ, Dunn DE: Anatomic correlates of noise induced hearing loss. Otolaryngol Clin North Am 12:493513,1979 9. Teopold HM: Degenerations in the ventral cochlear nucleus of the guinea pig after impulse noise exposure. Arch Otorhinolaryngol209:247-266.1975 10. Morest DK, Bohne A: Noise-induced degeneration in the brain and representation of inner and outer hair cells. Hear Res 9:145-151, 1983 11. Catlin FI: Guide for evaluation of hearing handicap. Otolaryngol Clin North Am 12:656-663,1979 12. Hall III JW: Peripheral auditory assessment, in Hall III JW: Handbook of Auditory Evoked Responses. Boston, MA, Allyn & Bacon 1992, pp 349-384