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The symptom referred to as tinnitus represents one of the most elusive mysteries facing hearing health care professionals. Even the pronounciation of the word tinnitus (tin' i tis or tin i' tis) remains unresolved. What is undeniable, however, is that this unwanted auditory symptom affects over 40 million Americans in a variety of ways [19]. In this chapter, some of the facts and myths surrounding tinnitus and its management will be reviewed.
DESCRIPTION
Tinnitus, from the Latin word tinniere (to ring), refers to any auditory perception not produced by an external stimulus. Commonly, tinnitus is described as a hissing, roaring, ringing, or whooshing. It can be tonal, ranging from high pitch to low pitch, multi-tonal, or noise-like (having no tonal quality). There is no absolute correlation between the perceptual quality of the tinnitus and the etiology responsible for this symptom, although some believe that certain pathologies, such as Meniere's Disease, is characterized by a low pitched roaring type tinnitus while other pathologies, such as noise induced sensorineural hearing loss, is more commonly typified by a high pitched tonal or hiss-like perception. Tinnitus may be constant, pulsed, or intermittent. Auditory hallucinations, which may be psychological or may have a true neurologic foundation, are not the same as the tinnitus discussed in this chapter.
Tinnitus may begin suddenly, or may arise insidiously. It is more prevelant in males, perhaps due to occupational patterns of noise exposure. There currently is no way to predict whether tinnitus severity will progress in a given patient, though most, but not all, report that there tends to be some degree of acclimation over time.
Tinnitus can be located in the ear, or ears, (tinnitus aurium) or in the head (tinnitus cranii). It may be perceived bilaterally or unilaterally. Meikle [20] has maintained a detailed tinnitus registry for the past decade for the American Tinnitus Association and found that 60% of the reported cases indicated their tinnitus was bilateral, 30% unilateral, and 10% stated the tinnitus was in their heads. Early reports of the loudness of tinnitus produced a great deal of confusion among professionals who were trying to associate the reported annoyance of the symptom with its apparent low intensity.
Vernon [37] reported that most patients matched their perceived tinnitus at 0-5 dB Sensation Level. This apparently low level did not agree with the subjective loudness reported by patients. It now appears that the tinnitus was assigned such a low intensity level due to the measurement technique employed. Vernon's subjects matched their tinnitus to tones presented ipsilaterally. Since most subjects matched their tinnitus pitch with a frequency that was characterized by elevated threshold, this meant that the monaural loudness balance match was confounded by the likely presence of loudness recruitment.
Goodwin and Johnson [6] later showed that if the tinnitus were matched to a frequency in which the hearing was not impaired (a monaural bi-frequency loudness balance), the loudness match increased to 24 dB as opposed to 6 dB when the tinnitus as matched to a frequency associated with impaired hearing. Tyler and Conrad-Armes [35] and Tyler and Stouffer [36] also confirmed the importance of the psychoacoustic technique utilized and also utilized sones, rather than dB SL as a measure of loudness.
CLASSIFICATION
Tinnitus can be broadly classified into two categories; objective and subjective. Under this classification scheme, the occasional presence of spontaneous tinnitus, a relatively weak, usually unilateral high pitched tone lasting less than a few seconds before gradually fading away, is excluded. Objective tinnitus, which may or not be audible to the patient, but is audible to an observer (either with a stethoscope, or simply by listening in close proximity to the ear) is present in less than 5% of overall tinnitus cases. In most instances, the cause of objective tinnitus can be determined and treatment, either medical or surgical, can be prescribed. Subjective tinnitus (audible only to the patient) is by far the more common, occuring in over 95% of patients.
CAUSES
Objective tinnitus: objective tinnitus is often associated with vascular or muscular disorders such as arteriovenous aneurysms, abnormally patent eustachian tubes, glomus jugulare tumors, palatal myoclonus, and spasms or tics of the stapedius or tensor tympani muscle. The tinnitus is frequently described as pulsatile (synchronous with the patient's heartbeat) and can be detected during immitance testing. There are some reports of objective tinnitus caused by abnormally intense spontaneous otoacoustic emissions, but these are relatively uncommon.
Subjective Tinnitus: subjective tinnitus is a symptom that is associated with practically every known otologic disorder and is in fact reported to be present in over 80% of individuals with sensorineural hearing loss [12]. This 80% figure undoubtedly underestimates the number of hearing impaired because audiometric data collection may not have included inter-octave frequencies, and frequencies beyond 8000 Hz.
The plethora of etiologies associated with tinnitus adds to the difficulty of finding a single, universal treatment. A partial list of conductive pathologies associated with subjective tinnitus is shown in Table 1 and a partial list of cochlear or auditory nerve lesions associated with subjective tinnitus is shown in Table 2. In addition, a review of drugs listed in the PDR offers a glimpse into the number of medications possibly producing tinnitus as a side effect.
Furthermore, there are a host of non-auditory pathologies which may be related to the perception of tinnitus. Moller [22] has speculated that ephaptic transmission, or phase locked spontaneous activity between damaged neurons, especially in the brain stem, could account for some of the non-auditory causes of tinnitus such as cervical injuries.
Anecdotal reports abound regarding tinnitus secondary to systemic diseases related to elevated cholesterol, elevated triglycerides, allergies, thyroid problems, diabetes, hyperlipidemia, hypertension, hypotension, syphillis, cardiovascular, endocrine, and metabolic diseases. In addition, tinnitus secondary to temperomandibular joint disorders, cervical injuries, obesity, menses, allergies, stress, dietary deficiencies, intake of stimulants such as nicotine and caffeine have been cited [30].
One phenomena that might seem logical to be associated with subjective tinnitus but is not, is the presence of spontaneous otoacoustic emissions. These sounds, which are apparently produced by the non-linear biomechanical action of the cochlea, particularly the outer hair cells, are present in approximately 50% of normal listeners.
Penner and Burns [25] and Wilson [39] failed to demonstrate any relationship between those individuals displaying spontaneous otoacoustic emissions and the presence (or absence) of subjective tinnitus.
Zurek [40] indicated that 50% of the 32 normal hearing subjects he studied presented spontaneous otoacoustic emissions, but none had tinnitus. Studies of evoked otoacoustic emissions, however, may yet prove to be useful, particularly with regard to patterns of contralateral suppression.
Patients suffering from tinnitus also may be classified as either being compensated or uncompensated. The majority of patients reporting tinnitus are able to satisfactorily cope with the symptom following simple reassurance. These patients are termed "compensated". The greater problem occurs for those patients whose ability to cope with tinnitus cannot be adequately served by simple reassurance. It is for these patients that many of the treatment strategies described later in this chapter are designed.
Further classification according to severity is based on subjective scaling or matching procedures. These topics will be discussed shortly. Classification with regard to severity is important for research purposes because research is often hampered by the Hawthorne effect.
Tinnitus patients represent a highly vulnerable and captive research population who may report improvement simply because they are pleased to know that a professional is "trying to help". Investigations employing experimental subjects having "mild" tinnitus are often helped by placebos, whereas experimental subjects having "severe" tinnitus are not. Therefore, future research should specify the severity of the tinnitus perceived by the experimental subjects.
PATHOPHYSIOLOGY
The exact physiological mechanism underlying tinnitus is unknown. It is likely that there are many mechanisms, just as there are many disorders producing this symptom. The lack of a definitive animal model of tinnitus has hindered investigations into pathophysiological mechanisms. Since salicylates and high levels of noise exposure are known to produce tinnitus in humans, animals injected with high dosages of salicylates and exposed to intense noises have served as test subjects.
Jastreboff, et al [15] have described a behavioral conditioning procedure for determining the presence of tinnitus in animals. Among the numerous mechanisms cited as producing tinnitus are: outer hair cell cilia decoupling from the tectorial membrane; hyperactivity of neural firing; hypoactivity of neural firing; ephaptic transmission; and improper functioning olivo-cochlear bundle function resulting in a lack of normal inhibition.
Even the site of tinnitus origin remains a mystery. While damage to the cochlea seems a likely site, considering the known damage occuring from such well established tinnitus producing agents such as salicylates and noise exposure, surgical severing of the 8th nerve with subsequent remaining tinnitus lends credence to a central, rather than peripheral origin. In fact, it could be postulated that the course of tinnitus is as follows: an acute insult (or offending agent) leads to a chronic signal which leads to a central modification which leads to psychological enhancement, which leads to intractable tinnitus. Thus, it is possible that an agent that produces a peripheral insult, ultimately results in a centrally perceived problem.
CLINICAL EXAMINATION
The clinical examination of the tinnitus patient should consist of at least a medical and audiologic examination and may also require a neurologic and/or psychologic evaluation. Regardless of who is the entry level specialist, a detailed questionnaire should be administered. This questionnaire should include, at the minimum, questions regarding...... time of onset, course, description of tinnitus, location of tinnitus, perceived cause of tinnitus, extent to which the patient is bothered by the tinnitus, exacerbating factors (such as food, stress, lack of sleep, etc.), drug intake, history of noise exposure, familial history of hearing loss or tinnitus, effect on sleep, and effect on personal/social/occupational relationships.
The Medical Examination: the medical examinationshould include some degree of assessment of the ear, nose and throat; cardiovascular system (elevated blood pressure, anemia, extensive arteriosclerosis); metabolic function (diabetes, hypo or hyperthyroidism, hyperlipidemia, vitamin deficiencies); pharmacologic factors (use of steroids, antibiotics, sedatives, antidepressants, nonsteroidal anti-inflammatories, salicylates; screening for possible TMJ disorders; screening for possible cervical abnormalities; serological studies; and if necessary, radiologic studies. It is the physician's responsiblity to determine how much diagnostic testing is appropriate for a given patient. This decision is not an easy one. The number of tests a distraught patient may request are exhaustive and cost prohibitive. On the other hand, a cursory medical examination is clearly not sufficient for an uncompensated tinnitus sufferer.
The Audiologic Evaluation: the audiologic evaluationshould include, at a minimum, threshold assessment (air and bone conduction, including inter-octaves 3KHz and 6KHz, and possibly the ultra high frequencies - it is best to use a warbled rather than a pure tone to minimize confusion with the tinnitus), word recognition testing, immitance testing, tinnitus matching, and measurement of masking ability and residual inhibition. Serious questions have been raised regarding the reliability of tinnitus pitch and loudness masking [24,36]. Even so, it is believed by some to be essential, particularly if masking is prescribed as a therapy. Even if masking is not being considered as a therapy, variability or changes in tinnitus matches may be useful as a means of monitoring other forms of therapeutic progress. Procedures for tinnitus matching are available [37].
The ability to mask an individual's tinnitus and the presence of residual inhibition (temporary absence or diminution of tinnitus perception following the termination of the masking stimulus) should be assessed in an effort to determine the likelihood of success with tinnitus masking instruments. The audiologist should be aware, however, that the intensity level required to produce masking may change over time [23].
Other audiologic procedures such as otoacoustic emission testing, auditory brainstem evoked response testing, electrocochleography, and additional site of lesion procedures should be administered, as required.
SEVERITY SCALING
There is no objective way to measure subjective tinnitus. Attempts have been made to utilize electrophysiologic methods such as auditory brainstem evoked response testing but the fact that most tinnitus patients also present a sensorineural hearing loss confounds the interpretation.
Because tinnitus, like pain, is subjective, two individuals may demonstrate identical loudness and pitch matches yet be affected in significantly different manners. The severity of the tinnitus then, is largely a function of the individual's reaction to the tinnitus (even though the reaction may not be totally independent of the actual pitch and loudness). Thus, it is imperative to assess the degree and manner in which the tinnitus affects a given individual. This can be done using subjective tinnitus severity scaling techniques. Several scales are available [5, 18, 34]. Used properly, these scales can be used as a baseline measure to assess therapeutic progress.
TREATMENTS AND CLINICAL MANAGEMENT
It is important to keep in mind that tinnitus is a symptom, not a disease. As such the optimal treatment strategy would be directed toward eliminating the disease, rather than simply alleviating the symptom. Unfortunately, of the multitude of etiologies responsible for producing subjective tinnitus, most are either untreatable or idiopathic. Therefore, most of the treatment attempts have been either non-focused, or have been directed at symptom control.
A wide variety of treatment attempts have been discussed in the literature. None have been totally successful, yet anecdotal reports have filtered their way into the lay literature and have been quickly embraced by a very vulnerable patient population. It is therefore the responsibility of hearing health care professionals to carefully analyze new reports of tinnitus managment procedures to determine the potential effectiveness, possible side effects, and cost efficiency of the treatments.
Attempts at tinnitus management can be reasonably categorized in the following manner:
Surgery: surgery should not be considered for tinnitus relief unless there is a clear indication that the underlying pathology can be surgically resolved. Previous reports of surgical intervention have yielded mixed success, at best, regarding tinnitus alleviation. Dandy [2] reported on over 400 patients on whom he sectioned the 8th nerve for Meniere's Disease. Only 50% reported an improvement in tinnitus. Similar results (45% reporting improvement) were reported [11] following translabyrinthine vestibular nerve sections. Vascular decompression surgery [21] has been suggested for patients with severe tinnitus and/or hyperacusis, but this remains a controversial topic.
Drug therapy: numerous medications have been prescribed for tinnitus patients. Some have been utilized for the purpose of minimizing the tinnitus itself, while others are directed toward alleviating the problems associated with the tinnitus (difficulty sleeping, anxiety, depression, etc.).
Drugs used for tinnitus alleviation have produced mixed results, with none producing lasting tinnitus relief without any side effects. For example, intravenous lidocaine or its oral analog tocainide was reported effective [3] but there may be side effects, including bone marrow supression, which preclude its long term usage. Some anticonvulsant drugs (tegretol, dilantin) have been tried. Amino-oxyacetic acid has been shown to reversibly decrease the endocochlear potential.
Reed, et al, reported tinnitus suppression in about one-third of their patients [26]. Guth, et al , propose the controlled use of the diuretic furosemide [8]. Risey et al, however, reported the side effects were "unacceptably high" [27]. Trental, a vasodilator reported to decrease blood viscosity and improve tissue oxygenation has been employed [30], but it too has potential side effects and should not be used for patients who are sensitive to caffeine and other methylaxanthines. Antihistamines have been used with success in a small percentage of patients. Most recently, calcium blockers have been employed. Results of double blind studies are not yet available, to this author's knowledge.
Medications used to alleviate problems associated with tinnitus include benzodiazepines (xanax, valium), antidepressants (prozac, nortriptyline or amitriptyline). While there have been recent reports claiming tinnitus reduction with benzodiazepines, it remains to be determined whether the tinnitus itself has been reduced, or whether the patient's ability to cope with the tinnitus has been improved because of less anxiety, better sleep, etc.
Anecdotal reports of reduced tinnitus following ingestion of certain non-prescription drugs or herbs have raised hopes for a "simple" cure for many years. Vasodilators such as niacin or nicotinic acid, herbs such as the extract from the ginkgo biloba tree and even Norwegian kelp have been reported to be useful for some patients. As with other more traditional drugs, however, none have shown consistent benefit when subjected to rigorous double blind experimental studies.
Nutritional management: although there has not yet been a definitive relationship established between nutrition and tinnitus, many tinnitus patients report that certain substances (i.e. caffeine, salt, some cheeses, red wine, foods containing MSG, etc.) exacerbate their tinnitus. In these instances, keeping track of apparent relations can help patients experiment with modification of their diet.
In addition, some researchers have indicated relationships between vitamin deficiencies. Shambaugh reported zinc deficiencies in his sample of tinnitus patients [29]. If such deficiencies can be definitively identified, vitamin or mineral supplements can be suggested. Megadoses of supplements should be avoided or monitored very carefully for side effects in other functions.
Masking: The use of an externally produced sound to either cover up, or in some way inhibit or alter production of tinnitus was first officially discussed in 1928 by Jones and Knudsen [17]. Fifty years later Vernon popularized masking as a viable way of treating some tinnitus patients [37]. Fortunately, most, though not all, patients report that an external sounds are effective in masking out the tinnitus perception. This, in addition to the fact that patients' attention is more occupied during the daytime, accounts for why so many patients report the tinnitus is most noticeable to them when they lie in a quiet bed.
Essentially, there are four main methods of providing masking: a tinnitus masker (an earlevel electronic noise producing device housed in a hearing aid case; a tinnitus instrument (a combination hearing aid and tinnitus masker), bedside noise generators; and hearing aids.
Initial reports on the success with tinnitus maskers seem to have been overstated. The early success rates approaching 80% have not been duplicated in other studies. Even so, there does appear to be a subset of tinitus patients who find the noise produced by the masker to be less annoying than that produced by the tinnitus, itself. Perhaps the patient's perception that 1) the masking noise is outside, rather than inside, the head is an improvement; and 2) the fact that the patient has direct control over the loudness of the masker (via a volume control) produces a palliative effect.
The fact remains, however, that a significant number of tinnitus sufferers merely find that after a short while the masking noise is little more than a substitute of one annoying sound for another. The use of tinnitus instruments may be applicable to a larger number of patients (providing the patient has some degree of hearing loss, as the vast majority of tinnitus sufferers do) because in addition to producing the masking noise, the instrument also amplifies environmental and speech sounds thus providing meaningful stimuli to the patient.
Conventional hearing aids, and certainly digitally programmable multiband compression hearing aids, have afforded professionals new flexibility with regard to shaping incoming amplified signals to help relieve the stress of straining to hear, mask out tinnitus, and amplification [28, 31]. In the past, some tinnitus patients complained that amplification exacerbated the tinnitus. In some of these cases, it is likely that there was excesive power being delivered to the ear in certain frequency ranges. Therefore, it is important that loudness growth be carefully measured prior to fitting hearing aids. Applying new knowledge of earmold acoustics and dynamic range syllabic compression further assists the professional in helping these patients.
Electrical stimulation and cochlear implants: the use of electrical stimulation has been discussed since 1801 when Grapengiesser found that an anodal current could suppress tinnitus perception, and that a cathodal current produced an auditory sensation but did not relieve tinnitus [7].
These finding were repeated nearly 160 years later by Hatton, et al [9]. More recently, the serendipitous finding that a significant number of patients receiving cochlear implants report a reduction in their tinnitus [14], has rekindled interest in this approach. Experiments with TENS (Trans Cutaneous Electrical Nerve Stimulation) units have met with mixed results [1, 4, 38]. At this time, electrical suppression cannot be considered a viable treatment approach until further studies are completed to determine:
1) the most effective electrical pathway,
2) the most effective stimulus waveform and intensity, and
3) the long term safety of electrical stimulation on tissue and on residual hearing.
Psychological interventions: regardless of the cause of tinnitus, the differentiation of the compensated versus the uncompensated patient is ultimately a function of how the patient reacts to the tinnitus. If a person is not "bothered" by the tinnitus, it ceases to be a problem. This is not to say that attempts should not be made to identify and, if possible, rectify the underlying disease process. But given the reality that most cases of subjective tinnitus are idiopathic in nature, psychological intervention aimed at successfully reducing the stress, distress, and distraction associated with the tinnitus can be very productive and often produce the most attainable goals. Many of the techniques reported to have produced success with the management of tinnitus patients have been borrowed from chronic pain management.
Stress and maladaptive coping strategies are manifested in a variety of manners, both physical and psychological. Tinnitus patients are well served by education concerning the undeniable correlation between exacerbation of tinnitus perception and stress. Stress management courses are offered for groups or individuals through community health organizations as well as through professionals. Individuals can learn how certain physical functions can be altered via mental control. Relaxation, guided imagery, and self-hypnosis are examples of self help methods used to help combat the stress, anxiety, and sleep disturbances associated with tinnitus by many patients.
Myogenic biofeedback with counseling may minimize tinnitus [10]. Biofeedback may alter multi-symptic transmission, like anti-convulsant drugs. In addition to facilitating relaxation, it has been shown to identify and alter physical stress loci that may contribute to tinnitus exacerbation. An example is biofeedback directed at reducing bruxism or TMJ stress.
It has been suggested that desensitization can be employed to assist the tinnitus patient. Drawing upon the principles of neural plasticity, Jastreboff [16] reported that a broad band noise presented to a patient can successfully produce an habituation to the tinnitus. It is emphasized that this noise is not utilized as a masker. In fact, the notion is underscored that initially, the tinnitus should be clearly audible along with the low level noise signal. Eventually, the brain relearns a pattern that will de-emphasize the importance of the tinnitus. It is also interesting to note that Jastreboff, et al believe this is a particularly useful therapeutic approach to patients suffering from hyperacuity, which they postulate is a precursor to tinnitus.
Drawing on the finding that the correlation between tinnitus loudness match and tinnitus annoyance is not particularly high, Sweetow [32 ,33] proposed that it is the patient's reaction to the tinnitus, rather than simply the presence of tinnitus that produces the problem.
Similar to its use with chronic pain patients, Sweetow supports cognitive-behavioral therapy as an adjunctive approach to managing the tinnitus patient. The purpose of this therapeutic approach is to modify maladaptive thoughts and behaviors by applying systematic, measureable implementation of strategies designed to alter unproductive actions. A reaction is a behavior, and all behaviors are subject to modification.
Reviews of the principles and practices of cognitive-behavioral therapy as they apply to the tinnitus patient are published elsewhere [32]. For the purposes of this chapter, suffice it to say that the basic flow of therapy entails the following steps:
1) define the problem,
2) identify the behaviors and thoughts affected by the tinnitus,
3) list the maladaptive strategies and cognitive distortions currently employed,
4) distinguish between the tinnitus experience and the maladaptive tinnitus behavior,
5) identify alternate thoughts, behaviors, and strategies,
6) devise and rehearse strategies that can be measured,
7) regularly assess success or failure of coping strategies. It is stressed that this type of intervention should produce success with 6-8 weeks. If no progress has been made during this period, it is probably not going to be successful.
In addition to these "adjunctive" psychological interventions, it should be noted that direct counseling from a trained psychologist or psychiatrist may be in order. Tinnitus patients have been described as rigid, desperate, obsessive, or neurotic [13]. Many present have additional problems contributing to tinnitus distress (i.e. divorce, money, occupation). Some have a history of depression. It is difficult to definitively state whether the emotional status of tinnitus patients existed before the onset of tinnitus, or whether it is a result of the tinnitus. The hearing health care professional must be prepared to recognize when an outside referral to a mental health professional is appropriate.
Because tinnitus is so misunderstood, even among professionals, and since there is no known cure for most cases of idiopathic, subjective tinnitus, good advice for patients is to become educated about the symptom. The American Tinnitus Association (ATA) has taken the lead in providing education materials for tinnitus sufferers. In addition to supplying individuals with brochures regarding various aspects of tinnitus, the ATA sponsors several support groups around the country. These support groups can either be peer directed by tinnitus patients, or can be professionally facilitated [33].
Alternative Approaches: There have been anecdotal reports of tinnitus alleviation following acupuncture and chiropractry but there are not yet any definitive studies justifying these approaches.
CONCLUSIONS
Despite the lack of a tinnitus "cure", it is unethical and immoral for a hearing health care professional to inform a tinnitus sufferer that "there is nothing that can be done for you, just learn to live with it". In this chapter, a variety of approaches have been discussed. Flexibility in thinking is needed and the patient must be made "a partner" in finding the best way to deal with this unwanted auditory disturbance.
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REFERENCES
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