Noise exposure is the most common cause of tinnitus. Noise induced permanent tinnitus (NIPT) can derive from occupational noise exposure, leisure noise or acoustic trauma. In general NIPT is high - pitched and tonal. The most common observed frequency of tinnitus on pitch matching is the same as the worst frequency for hearing. The sensation level of NIPT is usually low and sometimes negative. There is no correlation of significance between the discomfort caused by NIPT and audiometric findings. In occupational NIPT the interval between the start of noisy work and the appearance of tinnitus is long (many years) but with leisure noise and acoustic trauma the interval between exposure and tinnitus is frequently very short (immediate). It is a problem that the incidence of musically induced tinnitus is increasingly more common. It is also a much greater handicap for a young individual to suffer from tinnitus than from a small high tone hearing loss. Much more attention needs to be given to improve these matters. The treatment of NIPT is not different from tinnitus treatment in general.
Keywords: Leisure noise, occupational noise, tinnitus, pop/rock music
|How to cite this article:|
Axelsson A, Prasher D. Tinnitus induced by occupational and leisure noise. Noise Health 2000;2:47-54
| Introduction|| |
The relationship between noise exposure and noise-induced hearing loss (NIHL) on the one hand and tinnitus on the other, has been addressed in a number of articles. A review of these studies was presented a few years ago (Axelsson & Barrenas, 1991). A reason to examine the state of these things now is the change that has occurred in the industrial noise environment as well as in leisure activities.
The relationship between occupational noise and tinnitus can be assessed in different ways:
* The noise etiology in tinnitus patients.
* Noise-induced permanent tinnitus (NIPT) in relation to different types of noise and sound levels.
* NIPT in relation to NIHL and the extent of hearing loss.
The etiology for tinnitus can in most cases only be established on the basis of the history. It is fairly unusual for tinnitus to start suddenly with a clear relationship to a specific traumatic incident; in fact it is usually slow and insidious. This of course makes any attempt to establish a clear relationship difficult and in general the etiology is based on the occupational history, any other disease with possible connection to tinnitus, audiometric results and other tests including laboratory ones. So it can be held that the etiology is mostly a "best guess". In all investigations there is a predominance of cases under the headline "uncertain etiology". In our studies based on patients presenting to a tinnitus clinic it was found that noise exposure and NIHL were by far the most common cause of tinnitus (Axelsson & Barrenas, 1991). If acute "acoustic trauma" was included at least 1-in-3 cases were caused by noise.
There are obviously many different types of noise in the occupational environment: pure tones, narrow-band noise, broad-band noise, impulsive noise, continuous or intermittent, lowor high-pitched etc. and a large number of combinations.
There are very few investigations on the influence on hearing or tinnitus of these different physical properties of noise. The reason is the existence of a variety of noise parameters over time and the large individual variations of exposure not only due to differences in the work environment but also biological differences between individuals. Generally, it is considered that impulsive sound is more damaging to hearing than continuous noise and that pure tones are more harmful than composite sounds. Also, high-pitched sounds are probably more harmful than low-frequency sounds. Even less is known concerning the relationship between the physical properties of noise and a subsequent NIPT, but it seems reasonable to assume that factors that damage the sense of hearing also may elicit tinnitus more commonly.
A few investigators have examined specific populations exposed to occupational noise. The incidence of tinnitus in these different populations has varied much and it is probable that there are also a number of differences in the method of testing, definitions of hearing loss and tinnitus. The incidence of NIPT in these noise exposed populations is presented in [Table - 1].
As can be seen the size of the populations varies much and so does the prevalence of NIPT. There is some suggestion that the incidence of NIPT is higher amongst claimants than it is in others. It seems reasonable to suggest that between 20 and 40 % of the occupationally noise exposed workers "suffer" from NIPT.
In a study that we have performed on over 400 tinnitus patients in audiological practice we found that 33 % of the patients had previously been exposed to occupational noise (Axelsson & Barrenas, 1991).
Overall, there has been a surprisingly large variation in the incidence of NIPT in the literature and the reason for this is not clear. It also indicates that there is a need for more investigations in this respect.
Some investigators have addressed the question of a relationship between the amount of hearing loss and NIPT. In a previous study we found that there was a good correlation between the pure tone threshold at the worst testing frequency and the pitch of NIPT (Axelsson & Sandh, 1985). Since NIHL is predominantly affecting the high frequencies at 2 - 8 kHz this is also where the tinnitus pitch is most frequently found at pitch matching.
At loudness matching the sensation level of tinnitus (tinnitus loudness match - pure tone threshold) is mostly low and the most common sensation level is + 5dB. Interestingly, we found that the sensation level was sometimes negative which means that the indicated tinnitus loudness was lower than the pure tone threshold. We believe that this shows that it is difficult for the patient not only to truly indicate the hearing level but also the tinnitus loudness level.
In a comparative study of the degree of severity of tinnitus and the audiometric findings we have found that tinnitus was worse with more pronounced hearing loss [Figure - 1]. In this study all cases of tinnitus, regardless of etiology, were included, but the most common etiology of tinnitus was noise exposure and NIHL.
We have tried to investigate the interval between the start of exposure to occupational noise and the appearance of tinnitus (Axelsson & Barrenas, 1991). With all reservations for the large differences in the physical properties of noise in different professions and also the difficulties in assessing the time of onset of tinnitus, we found large differences between the workers in different professions [Table - 2].
In the occupational environment there has been a pronounced change concerning noise lately, at least in the developed countries. A number of positive improvements can be listed:
* An improved awareness of the noise problems
* An increased appreciation of preserved hearing
* A more quiet work environment
* Better hearing conservation programs
* Improved technical noise abatement
* Improved ear protectors
* Improved use of ear protection
* Regular and repeated industrial audiometry
* Early identification of NIHL
* A considerable increased public information on these matters
As a result of this, there is reason to assume that hearing is better preserved these days and as a consequence the incidence of NIPT is decreasing. However, there are no follow-up studies available which have examined the sound levels in industry or the incidence of NIHL in noise exposed occupational populations in a regular manner over time. In spite of this we believe that noise exposure has diminished in industry with a subsequent decrease in NIHL and NIPT.
This has resulted in a shift of the etiology of NIHL and NIPT from occupational noise to environments with recreational noise exposure. With the increasing interest in noisy recreational activities this etiology of NIPT has become increasingly more common. However, so far there are no studies available giving solid figures in these matters.
- NIHL is the most common cause of tinnitus.
- The literature shows a very wide range of tinnitus due to NIHL.
- NIPT on average appeared 23 years after start of noisy work.
- NIPT onset was slow except for acute acoustic trauma.
- Tinnitus was correlated more with hearing threshold than with age.
- Tinnitus severity generally increased with worsening hearing.
- Tinnitus was most often tonal and high pitched.
- Tinnitus pitch was most frequently localised at the worst hearing frequency (at the bottom of the noise notch).
- Tinnitus sensation level (tinnitus loudness - hearing threshold) was mostly small and sometimes negative.
- Tinnitus quality was more often tonal than noise.
- Tinnitus was most often bilateral but much more common in the left than in the right ear.
Tinnitus induced by leisure noise
At the same time that occupational noise exposure probably has decreased, the situation with noisy leisure activities is probably going in the other direction. With more and more leisure time there has been an increase in recreational activities of which many imply noise exposure. Children are exposed to noisy toys and games and the market is "developing" rapidly (Axelsson & Jerson, 1985). The attitudes of the manufacturers of such toys is generally not to consider the possible risk of damaging the sensitive hearing organ.
At adult age there is an ever-increasing number of new noisy activities many of them in connection with music (Axelsson et al., 1981; Axelsson, 1996). The interest in hunting and target practice has always been high amongst males and the attitude to personal ear protection has been poor.
The most marked difference from the industrial environment is the lack of responsible action during recreational activities. It is up to each individual to protect himself. Therefore knowledge about risks, sound levels, early symptoms etc are extremely important.
The severity of NIPT in relation to different activities
We have developed a severity grading of tinnitus based on 10 questions (Coles et al., 1992). The questions are presented in [Table - 3] and we use an arbitrary point scale. The maximum severity is 44 points. The distribution of severity in a clinical tinnitus material shows a fairly even distribution between 15 and 40 points. The average in our tinnitus clinic was 26 points.
In clinical practice we use a questionnaire concerning noise exposure during childhood, military service, occupational noise and recreational hunting and target practice. The results are shown in [Table - 4],[Table - 5],[Table - 6]
Regarding the difficulties for adult people to remember the amount of exposure to noise during childhood we adopted a simple quantification as seen in [Table - 4]. Most respondents considered that they were exposed to an average amount of noise and there was no correlation to the severity grading of tinnitus.
For military noise exposure [Table - 5] there was predominance of average or less than average noise exposure. Provided that the population had at all been exposed to noise there was no correlation between tinnitus severity and the amount of exposure but those not exposed at all rated a less severe tinnitus.
For recreational shooting the severity of tinnitus was regarded worse both for those practising hunting and target shooting than for those who did not [Table - 6].
When we examined the severity of NIPT in relation to occupational noise exposure, those who not worked in noise reported a severity grading of 22 points, less than the average for our tinnitus patients. For those who had worked in noise there was no difference if they had been exposed "seldom", "often" or "always" and the severity of tinnitus was rated 28 - 29 points.
In summary there seems to be a more severe tinnitus for those who have been exposed to noise in military service and those who have used weapons during leisure time. It can be assumed that this also shows that tinnitus is more severe for those exposed to impulsive noise.
Tinnitus induced by music exposure
Over the last 25 years there has been a large number of publications concerning the possible harmful influence of loud modern music on hearing. Some authors have found hearing losses (Babisch & Ising, 1989) but others have not been able to do so (Axelsson & Lindgren, 1977). Generally, the problem has been widely exaggerated and it is not uncommon to hear statements like: "We are leaving a deaf generation behind". Now, we have studies with a follow-up of 20 - 25 years, which are not able to demonstrate an increased prevalence of hearing loss in young individuals from exposure to loud music (Axelsson et al., 1993; Hetu & Fortin, 1995; Hoffmann, 1997).
Interestingly, in contrast to the large number of publications concerned with hearing loss and music, there are hardly any publications addressing the possible occurrence of tinnitus after music exposure. Furthermore, a small high tone hearing loss is hardly noticed whilst a NIPT, present day and night has a much more distressing effect on the affected individual.
While NIPT from occupational noise is decreasing in clinical practice it is more and more common that young patients report tinnitus acquired from exposure at pop/rock concerts or after visiting a disco (Bradley et al., 1987; Babisch et al., 1988; Ising et al., 1988). This of course, is alarming and actions should be taken rapidly in order to improve matters. Clearly, the thought for a young individual to realise that he/she will have to live a whole life with tinnitus is a severe psychological trauma.
On the other hand there are no studies available trying to address the question of how frequently tinnitus occurs after musical exposure (Hetu & Fortin, 1995). As is wellknown there is also a very high number of exposures of this kind each year all over the world and hopefully the risk of acquiring tinnitus is small.
There are no special risk criteria for recreational noisy activities including music. The risk of hearing loss depends upon sound level, exposure time, type of sound and individual biological variations in sensitivity. Provided that there is no occupational noise exposure, it is probably "safe" for most individuals to attend a disco with a typical 97 - 100 dBA musical "noise" once a week for a couple of hours for many years with little risk of acquiring a hearing loss. However, the appearance of NIPT is much more erratic and most of the affected individuals cannot explain why a particular rock concert or disco visit elicited the tinnitus in general without concomitant hearing loss.
It is quite obvious that many more studies need to be done to assess the problem of musically induced NIPT.
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Institute of Laryngology and Otology, University College of London, 330 Gray’s Inn Road, London WC1X 8EE
Source of Support: None, Conflict of Interest: None
[Figure - 1]
[Table - 1], [Table - 2], [Table - 3], [Table - 4], [Table - 5], [Table - 6]