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Introctuction Hearing sounds that do not originate in the world outside the body is an experience that probably every human has at one time or another in life. The sounds heard range from popping and clicking to intermittent roaring and buzzing to continuous pure tones. In their diversity, these experiences have two things in common: they all originate, in one way or another, from inside the head, and they are all known as tinnitus. Tinnitus can accompany a wide array of serious and minor disorders of the ear and of the body in general. As shall be seen, some causes are reasonably well under- stood, but most are not. Effective palliative treatment has been established for some forms of tinnitus, but for most, effectiveness of treatment continues to be unpre- dictable. The following section provides an overview of the tin- nitus problem and of the various topics that are discussed in detail in subsequent sections. OVERVIEW OF THE REPORT Tinnitus can be defined as the conscious experience of a sound that originates in the head of its owner. In some cases tinnitus exists because there is actually a source of acoustic energy located somewhere in the head and neck area--a contracting muscle, a clicking jaw, a defective vein or artery, etc.--that can also be heard by a second party, with or without the aid of special devices. How- ever, the majority of tinnitus cases have no detectable acoustic basis, but instead arise from anomalies in one or more of the elements of the neural chain that consti- tutes the auditory nervous system. It is important to 1
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2 emphasize at the outset that tinnitus is itself not a dis- ease, but a symptom that is common to many maladies that afflict many different structures within and without the auditory system. A frequently drawn analogy is to fever and headache--symptoms that accompany many different dis- orders. Like those two symptoms, tinnitus can range in severity from mild and easily overlooked to severe and debilitating. Existing estimates of the prevalence of tinnitus are all flawed in one way or another, but all are in accord over its ubiquity. A recent British survey indicates that about 1 percent of the general population has severe, occasionally debilitating tinnitus; were this percentage an accurate estimate of prevalence in the United States, there would be about 2.5 million Americans afflicted with severe tinnitus. At the other extreme, it may be that nearly everyone experiences a mild form of tinnitus at one time or another in life and thus that mild episodes of tinnitus are "normal" in the sense that an occasional backache or pimple is normal. The majority of tinnitus cases are probably never re- ported as medical or auditory problems, but are simply accepted as normal phenomena or as occasional minor irri- tants. For some people, however, tinnitus can become as totally debilitating as any serious systemic disorder. It can be severe enough to turn an otherwise healthy, well-adjusted person into someone unable to work or so- cialize. Anecdotes persist about people committing, or threatening to commit, suicide because of severe tinnitus and of others begging to have their offending ear surgi- cally destroyed in the hope of escaping a relentless tin- nitus. Every experienced hearing specialist has seen less severe, but nevertheless serious, cases. Given the multiple origins of tinnitus, it should be expected that no single treatment for tinnitus is likely to be found. Also, it should be no surprise that many forms of treatment have been attempted over the years. Unfortunately, few of these have had much success until recently. Indeed, until lately, hearing specialists have had little to offer tinnitus sufferers in the way of re- lief, and far and away the most common "treatment" even for severe tinnitus has been the statement that lots of other people have the problem, that there is nothing much that can be done about it, and that the patient will simply have to learn to live with it. This grim situ- ation has brightened considerably, however, and the prospects now appear good that the symptom of severe
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tinnitus will eventually be alleviated for a substantial fraction of its sufferers. The two most promising areas of advancement in the treatment of tinnitus involve drugs and masking. In the past few years, several drugs have been iden- tified as potent agents against several of the common forms of tinnitus. These include lidocaine, carbamaze- pine, and sodium amylobarbitone. So far each has draw- backs of one sort or another that prevent its immediate widespread use, but related drugs are being developed and studied. Many tinnitus sufferers independently discover that sounds from the external world can cover up or mask their tinnitus. Such people realize relief in relatively noisy environments or from background sounds such as the inter- station noise on a radio. Hearing specialists have known about the effectiveness of masking against tinnitus for decades, but not until recently was it offered in a systematic way as a palliative for tinnitus. In the mid-1970s a group of hearing specialists at the University of Oregon Medical School developed a device for generating a masking sound that could be mounted in a standard hearing aid chassis. This tinnitus masker was later combined with a hearing aid in the same chassis, and this combination was called a tinnitus instrument. For about 5 years, tinnitus maskers and instruments have been prescribed and distributed to tinnitus patients com- ing to the Oregon tinnitus clinic. The primary question posed to CHABA Working Group 89 was to evaluate the efficacy and safety of tinnitus maskers/instruments. Nearly all the available information on efficacy comes from follow-up questionnaire data collected, collated, and published by the Oregon group. Their series of re- ports contains some inconsistencies and some (perhaps understandable) exaggerations, but overall the outcomes are encouraging. It is important to remember in what follows that the Oregon group surely does not see a ran- dom selection of tinnitus sufferers, but rather, those severely enough afflicted to be motivated to travel to the clinic (and affluent enough to be able to). That is, the patients in the Oregon sample probably include some of the most severely afflicted tinnitus sufferers in the country, and the various success rates should be interpreted accordingly. There are a number of reasonable ways to calculate estimates of success from the Oregon data; the basic issue is what number is most appropriate for use as the
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4 denominator of the success ratio. About 25 percent of the people who appear at the Oregon clinic are sent away without a recommendation to try a masker, hearing aid, or instrument, and this number has been essentially constant over the years. If these people are included in the de- nominator when calculating a success ratio, the estimates obtained are very conservative ones. Less conservative estimates are obtained by excluding this 25 percent of the people from the denominator on the grounds that they were not regarded to be good candidates for masking and thus should not be "counted against" the success of the treatment. Still less conservative estimates involve excluding both this 25 percent and those people who were given a recommendation for one of the three devices- - masker, aid, or instrument--but who did not purchase one after the trial period. Depending upon which of these increasingly less conservative denominators is used, be- tween about 42 percent and 83 percent of the respondents to the Oregon clinic's questionnaire report either total or partial relief from their tinnitus through use of the recommended devices. Considering the presumed degree of tinnitus severity in this sample, such success rates are certainly encouraging. Masking of tinnitus is not a panacea, but from these statistics, and from the absence of other, equally effective treatments, masking must now be regarded as the treatment of first choice. m e primary reason for caution regarding this conclusion is that at present essentially all of the data on efficacy originate from a single source. The safety of tinnitus maskers/instruments is more difficult to evaluate at this time than is their efficacy There are several reasons for this. First of all, there is essentially no information available about the sound- pressure levels (SPL) experienced by typical wearers of tinnitus maskers/instruments, nor about the temporal pat- terns of these exposures. Such information is crucial, of course, if safety is to be evaluated by consulting standard damage/risk criteria or exposure guidelines. Most tinnitus maskers/instruments have maximum outputs of 85-95 dBA, and some are rated as high as 105-110 dBA. The most widely used U.S. exposure guideline permits ex- posure to 90 dBA for only 8 hours per day when the exPo- sures occur 5 days per week. Emus, nearly all currently available maskers/instruments are capable of exceeding common damage/risk criteria and therefore have the poten- tial to produce hearing loss.
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5 mere exists a serious question, however, of whether tinnitus maskers/instruments should be regulated on the basis of their presumed, or even demonstrated, risk to hearing. The issue is that for many thousands of people tinnitus is a severe, debilitating condition, and it can be argued that the risk, or even the inevitability, of some additional hearing loss caused by a masker/instrument is a price worth paying for the relief from the tinnitus. An obvious parallel exists with hearing aids. Evidence is accumulating that the levels and durations experienced by many wearers of hearing aids may eventually cause addi- tional hearing loss, yet few hearing professionals regard that risk (or inevitability) to be serious enough to war- rant restricting the availability or use of hearing aids, nor presumably would hearing-impaired people be willing to forfeit their aids on these grounds. Similarly, cer- tain drugs carry long-term risks (or inevitabilities) that do not rule out their use when they are all~that is available for treatment of a serious malady. It appears that for the moment the best policy to follow in regard to the safety of tinnitus maskers/ instruments is to make users explicitly aware of the virtues for hearing conservation of low masker levels and of intermittent patterns of exposure. Until more is known about the levels and durations of exposure experienced by typical users of tinnitus maskers/instruments, more re- strictive policies are premature, and even when more is known, such policies may be judged inappropriate. In summary, after years of neglect, tinnitus is rapidly coming to be a topic of active interest to clinicians, physiologists, psychoacousticians, and other hearing spe- cialists. Much is left to be learned, but it is clear that tinnitus is now an established, legitimate research area; it is not dust another buzz word. In the rest of this report, the issues briefly men- tioned here are examined in more detail, and the evidence on which current beliefs about tinnitus are based is presented and evaluated. A DEFINITION OF TINNITUS As is true for so many phenomena, a concise yet precise definition of tinnitus is difficult to achieve. As noted, one distinguishing feature of tinnitus is that the origin of the perceived sound is inside the head. In some cases there is an actual sound source--a vibrating body--under
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6 lying the perception. Some examples are vascular anoma- lies, muscular contractions, clicking jaws, and even trapped insects. Obviously, the existence of such sound sources raises the potential for their being detected by others, with or without the aid of amplifying devices. Indeed, some truly remarkable cases have been reported. Glanville et al. (1971) discussed a case of a young child having a high-pitched tinnitus that could be heard at a distance of 4 feet. The child's father and one of its two siblings had similar, but less dramatic, emissions, and, interestingly, the father was unable to hear his own emission. Huizing and Spoor (1973) also reported on a patient whose ear emitted a high-pitched tone that was audible to a 1 but herself. She, and the father mentioned previously, had circumscribed hearing losses in the ~- tral region of their emissions. Thus, technically speak ~ no , newer naa c~nnzcus, since they could not hear their own sounds. Other examples of intense emissions have been noted (see Zurek, 1981), one in a dog (Decker and Fritsch, 1982) and one in a cat (CIBA Foundation, 1981:133). A long-standing distinction in the tinnitus literature is between those instances of tinnitus that have a vibra- tory origin and can be heard by others, as well as by the patient, and those instances in which the tinnitus is audible only to the patient, presumably because the site of origin is inside the nervous system and there is no vibratory concomitant. Various dichotomies have been proposed for these two forms of tinnitus: for example, vibratory/nonvibratory (Fowler, 1939, 1941), objective/ subjective, extrinsic/intrinsic (Atkinson, 1947), pseudo/ true (Jones and Knudsen, 1928). me intent behind the distinction, of course, is to partition instances of tin- nitus into two broad categories as an initial aid to diagnosis and treatment. Problems with all of these dichotomies have recently been spotlighted by the development of new procedures for monitoring acoustic activity in the outer ear canal (Kemp, 1978). The facts are discussed at length in the section " m e Objective/Subjective Issues in Chapter 2; all that need be noted here is that with these new techniques, weak acoustic activity has been found to underlie some instances of tinnitus that previously had been categorized as subjective or nonvibratory. The point is that there are a number of factors that can affect the ability of a person to detect a sound, and failure by a clinician to do so cannot reasonably be taken as evidence for the nonexistence of the sound. So, while these various di
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7 chotomies are well intentioned, application of the cri- teria has been, and surely will continue to be, much more difficult than was initially apparent. Even more refined procedures may eventually reveal acoustic concomitants of other forms of tinnitus, thereby moving them from the sub- jective to the objective category, and conceivably, non- acoustic but nevertheless objective measures of some forms of tinnitus may be developed that will further muddy the distinction between objective and subjective forms of the malady. To the extent that treatment and scientific in- sight are dependent upon such categorizations, there is a need for a new appreciation of the shortcomings of the objective/subjective, vibratory/nonvibratory, and other dichotomies. While these distinctions are sometimes used in this report, our commitment throughout has been to the view that objective measures may eventually be developed for many, if not all, forms of tinnitus. It should be noted that a recent major publication on tinnitus (CIBA Foundation, 1981:Appendix I) explicitly proposes to exclude from the definition of tinnitus those cases previously classified as objective. While the objective/subjective distinction may have become muddy in recent times and may deserve to be dropped (see " m e Objective/Subjective Issue" in Chapter 2), there is no apparent justification for disregarding history and tradi Lion by excluding from the definition of tinnitus those ahead noises" that happen to have an acoustic concomitant In this report, then, the term tinnitus is used to describe the conscious experience of a sound that origi- nates in the head, either acoustically or physiologically. For inclusion in the definition, no criterion of severity, loudness, annoyance, or other characteristic of the tin- nitus need be met. A distinction not made by this defini- tion, but which will eventually have to be drawn, is be- tween the elementary sensory experiences of the tinnitus sufferer and the organized perceptual experiences of the hallucinating mental patient. PREVALENCE OF TINNITUS - It is apparently widely believed that mild, occasional tinnitus is experienced by nearly everyone at some time or another and that these brief episodes are not neces- sarily associated with, or precursors to, auditory path- ology. Given this belief, it is peculiar that most formal
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8 attempts to estimate tinnitus prevalence do not effec- tively discriminate such instances of tinnitus from its severe, annoying, and protracted forms, nor do they dis- criminate between the tinnitus of normal-hearing and hearing-impaired subjects. The ambiguity of past ques- tionnaires and interview questions surely is a signifi . . . . . . cant source ot variability in prevalence statistics. Nevertheless, over the years, the following prevalence statistics have been reported: 1. About 32 percent of all U.S. adults report having had tinnitus at one time or another, and about 6.4 per- cent of that same population characterizes the tinnitus as severe or debilitating (National Center for Health Statistics, 1968). 2. About 85 percent of 2,000 consecutive patients seen by an otologist complained of tinnitus (Fowler, 1944). 3. About 83 percent of 500 consecutive patients with acoustic neuromas had tinnitus (House and Brackmann, 1981). 4. About 79 percent of 190 patients with otosclerosis had tinnitus (Glasgold and Altmann, 1966). 5. About 75 percent of all cases of deafness report tinnitus (Heller, 1955). 6. About 13 percent of school children with audio- metrically normal hearing report having tinnitus, at least on occasion (Nodar, 1972). 7. About one-half of a sample of deaf children had tinnitus (Graham, 1980). 8. Tinnitus prevalence increases with age up to about age 70 and declines thereafter (Reed, 1960). A recent British survey (Institute of Hearing Research, 1981) has attempted to use less ambiguous questions than those used in the past in order to better discriminate be- tween chronic, problem tinnitus and occasional, ~normal" tinnitus. Of course, the information obtained may not generalize perfectly to the U.S. population. Neverthe- ~ess, preliminary analyses indicate that about 17 percent ~ ~ . . . . of the British population sampled had problem tinnitus, that about 1 percent had tinnitus that produced severe annoyance, and that about 0.5 percent had tinnitus that resulted in an inability to lead a normal life. About equal percentages (9-10 percent) reported tinnitus with and without apparent hearing impairment, fewer reported unilateral tinnitus than tinnitus in both ears or "in the
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9 head," prevalence increased with age, and there was little sex difference in prevalence rate. (Note that if the 0.5-1 percent value does apply to the present U.S. popu- lation, it would mean that approximately 1.2-2.3 million people have severe or debilitating tinnitus.) Some authors have attempted to estimate tinnitus Preva lence In various subgroups or nearing-impaired people. These attempts are typically plagued by small sample size and other sampling problems. Nevertheless, Heller and Bergman (1953) studied 100 consecutive patients at a Vet- erans Administration audiology clinic and found that 73 percent had tinnitus. m e preponderance of these (39/100) were diagnosed as perceptive deafness, with conductive deafness (13/100) and otosclerosis (8/100) being the two next most common categories. Reed (1960) reported that in a sample of 200 patients referred for severe tinnitus, 38 percent were diagnosed as suffering Primarily from presbyousis, 16 percent primarily trom acoustic trauma, 12 percent primarily from Meniere's Disease, 10 percent from idiopathic symptoms, and the remaining 24 percent from a variety of other maladies. J. T. Graham (1965) distilled some data from Heller showing that tinnitus is reported by 71 Percent of those whose hearing impairment . . _ . . , ~ was diagnosed as perceptive, by en percent or those alag- nosed as conductive, by 88 percent of those diagnosed as combined, and by 85 percent of those diagnosed as oto- sclerotic. One unexpected fact has been found in some surveys of tinnitus. It appears that monaural tinnitus is about 1.5 times more likely to occur in the left ear than in the right (Hazel!, 1981b; Institute of Hearing Research, 1981). Verification should precede attempts at explana- tion (see CIBA Foundation, 1981:31). While the various official attempts to estimate tin- nitus prevalence are subject to various procedural criti- cisms, the resulting estimates do imply two things: that the magnitude of the tinnitus problem has not been appre- ciated and that effective treatment of tinnitus has not been available. Whenever there is an ignored, afflicted population of this size, the potential for abuse by char- latans and misguided healers is great, as is the risk of exaggerating the effectiveness of any new treatment. Caution and critical restraint must be exercised when evaluating new or modified treatments, and that has been the attempt throughout the preparation of this report.
Representative terms from entire chapter: