In this first part of a two-part series, Dr Sean Flanagan looks at the most common types of tinnitus
Tinnitus is a very common symptom and is classified as the perception of a sound in the absence of an external auditory stimulus.
Approximately 15% of the adult population report some degree of tinnitus, with approximately 2% of those describing it as a distressing symptom.1
In general terms, it becomes more common as we age, and this is essentially related to worsening hearing.
Tinnitus can be classified as either subjective or objective.2 Subjective tinnitus is a sound that cannot be detected externally, and is by far the most common form, and is usually initiated following damage to the inner ear.
Traditionally, objective tinnitus is described as a sound that an examiner can hear. Most of what we think of as objective tinnitus is related to the transmission of sound to the ear, and is often not audible to the examiner. Therefore, I would classify this as conductive tinnitus.
Pulsatile tinnitus falls under this category and is most commonly the result of eustachian tube dysfunction and other inflammatory conditions of the middle ear, while vascular tumours and anomalies must be considered and excluded.
Other forms of conductive tinnitus include middle ear and palatal myoclonus, and the transmission of nasal respiration into the ear via a patulous eustachian tube.3-5
SUBJECTIVE TINNITUS
Patients can often describe the sensation coming from one ear, both ears, or centrally. It can be described as a ringing, hissing, machinery, or cicada-type sound, among many others.
It can be soft and intermittent but can also be constant, and very intrusive, to the extent that it can affect concentration, sleep, social enjoyment and even cause suicidal ideation.6
As this is a subjective symptom, quantification of severity is based on a patient’s description of its effect on their daily functioning and quality of life. There are a number of well-validated questionnaires that can be used in this regard, such as the Tinnitus Handicap Inventory.7
The way to think about this (and to counsel the patient) is that following a degree of damage to the inner ear, the brain and the ear set up an alternate neural pathway, that eventually reaches the auditory cortex. This alternate neural pathway travels through various parts of the brain that include areas that control the jaw muscles, neck muscles and the limbic system.
Practically, this means that any form of emotional or physiologic stress can amplify the sensation of tinnitus. What often occurs is that tinnitus itself is irritating and this leads to activation of the limbic system which, via a feedback loop, further exacerbates the tinnitus.
The natural history of most cases of tinnitus is that the patient gets used to the sound or habituates to it.
Once an underlying serious cause is excluded nothing further needs to be done. It is in those with more severe tinnitus and associated symptoms that a range of management options should be considered.
PATHOPHYSIOLOGY
There is no absolute explanation for all subjective tinnitus, but it is likely generated by neurons of the ascending auditory pathways and/or by neural structures that are not normally activated by sound following some form of injury.8
The commonest is temporary and follows exposure to loud noise. This is the ringing sound experienced after being in a night club or at a concert.
Occasionally, severe noise exposure, especially of an impulsive nature, can leave one with permanent tinnitus. Age, genetic susceptibility, accumulated noise exposure, infections, trauma, Meniere’s disease, otosclerosis (especially with cochlear involvement), and more serious pathology, such as a vestibular schwannoma, can all be causes of auditory damage and thus tinnitus.
Toxins and some medications can also be responsible. The commonest of these are aspirin and other NSAIDS, aminoglycosides, loop diuretics, cisplatin, antidepressants, antipsychotics and antiepileptics. Almost all medications have at some stage been associated with tinnitus, but usually this is coincidental. Other common exacerbating agents are caffeine and alcohol.
As described above, an initial injury leads to generation of the tinnitus which is then modified by central connections to the limbic system and trigeminal nucleus that influence neck and jaw problems. This has been described as the “generator-preceptor” model of tinnitus.
The modern approach to tinnitus often parallels the management of chronic pain, and as a way of explanation can be likened to phantom limb pain following amputation.
INVESTIGATIONS
Following a thorough examination, a formal audiogram is the most important initial investigation.
With unilateral tinnitus, pulsatile symptoms, and/or asymmetry in the sensorineural thresholds, imaging of the central auditory pathways is important to rule out the presence of any central pathology. If there are no contraindications, an MRI scan of the brain and cerebellopontine angles and internal auditory canals is the best modality.
With symmetrical symptoms, imaging is not required, but a review of basic haematology, biochemistry and thyroid function tests are worthwhile.
MANAGEMENT OF SUBJECTIVE TINNITUS
One of the common mistakes in initial management is to tell patients that there is nothing wrong and that it is entirely in their head.
During the initial assessment it is important to spell out that the initial aim is to rule out any serious underlying causes (which are very rare) and then to minimise the intrusiveness of tinnitus.
It is very important to say that there are many things that can be done, but it is also important to state that the quest to completely get rid of the tinnitus is counterproductive. The goal is to make it unobtrusive.
Most people with tinnitus get used to the sound or habituate to it, and therefore do not require any specific treatment.
If it is a troubling symptom, then this requires a multifaceted, multidisciplinary approach which can be divided into ear (audiologic) and non-ear modalities.
AUDIOLOGIC MODALITIES
Sound therapy and masking: This involves introducing a broad-band sound at a low intensity which stimulates the normal auditory pathways and thus inhibits the alternate (tinnitus) pathways. This is commonly manifested in people who only notice their tinnitus when there is no or minimal background sound.
Simple ways of doing this is to use the radio off the station or leave a fan on in the room. There are also several apps available, for example, “white noise” or “sleep pillow”, and audio files available to play at a very low volume. One should have the volume of the white noise just below that of the tinnitus and over a period of time reduce the volume of the masking noise. This is designed to help the habituation process.
Improving hearing: This can be as simple as removing wax from the ear. Often the hearing is normal or near normal, and if this is the case, not much can be done in this area. Occasionally there may be a medically or surgically correctable cause of the hearing loss, such as a perforated tympanic membrane.
Hearing aids: In significantly intrusive tinnitus with any more than mild hearing loss, consideration of hearing aids needs be made, even if patients do not identify that their hearing is a problem. In this situation, the hearing aids act by increasing the volume of ambient noise and taking some “hearing stress” off the ear.
Often patients will feel that it is their tinnitus causing a degree of hearing loss, but it is usually the other way around. It is interesting that even when the hearing aids are removed, that the degree of tinnitus is still improved.
There are also hearing aids that have inbuilt masking devices that many patients find helpful.
The combination of severe tinnitus and severe hearing loss is difficult to manage, as a standard hearing aid is unable to amplify sound adequately to impart a benefit. It is in these cases where cochlear implantation can make a significant improvement to quality of life.9 This allows direct stimulation of the cochlear nerve itself, vastly improving hearing and in almost all cases significantly improving tinnitus.
Both surgical techniques and device design continues to evolve allowing successful implantation with a reasonable level of residual hearing.
Additional devices: There are a number of proprietary devices, such as the Neuromonics device, that have been shown to be effective in selective cases, especially in those with essentially normal hearing.10 The aim is to use a specific sound program to assist in habituation of the tinnitus and sensibly focus on the aberrant central connections that have been established. These devices can be expensive, so tend to be used as a last resort.
Prevention: Acoustic trauma can be a further exacerbating factor. Limiting significant noise exposure is important to minimise further damage and exacerbation due to noise.11,12
Ironically, as tinnitus is associated with hearing loss, the ear is also more prone to further damage from noise and it can also cause physical discomfort. A condition called hyperacusis, or sensitivity to noise, can accompany tinnitus. In this setting it is important to protect the ear from loud noise but to avoid blocking out normal environmental noise, as this can further exacerbate the sensitivity to noise.
It is interesting to note a rock concert at 100dB can damage hearing in just 15 minutes and louder sound, such as aeroplanes which are at 110 dB, can cause damage in just one minute. A study by researchers at the National Acoustic Laboratories (NAL) of Australian Hearing estimates that listening to music through headphones at 94dB for one hour can start to impact hearing.11
NON-AUDIOLOGIC MODALITIES
The non-audiologic measures involve down regulating any physiological or emotional stress for patients.
It is important to institute cognitive behavioural therapy to help manage stress and/or lack of sleep, as this can further exacerbate tinnitus for many patients.
Other components include treating neck and jaw problems with dental devices, soft tissue massage, physiotherapy and acupuncture. 8, 13-18
Psychological management: Often explanation of the symptoms, and the underlying cause and exacerbating factors, with the exclusion of significant pathology, is all most patients are seeking.
This situation often then leads to a vicious feedback loop where, as the tinnitus becomes more intrusive and distressing, further activation of the limbic system leads to further exacerbation of the tinnitus. In extreme cases patients can present with severe anxiety, depression and even suicidal ideation.6
Of all the treatments for subjective tinnitus, tinnitus retraining therapy (TRT) is the only modality that has definitively shown a positive effect.2, 16, 19
This is directed counselling using components of cognitive behavioural therapy and biofeedback and is conducted by a clinical psychologist with an interest in the area. A referral under the GP mental healthcare plan is very helpful.
Pharmacologic: Many herbal medications and supplements have been suggested in the treatment of tinnitus. Of all these, ginkgo biloba has been shown anecdotally to improve symptoms in some patients, although there is no evidence.15 I usually offer this as a trial for a couple of months as it has a very low risk profile.
Occasionally pharmacological treatments are considered as short- to medium-term circuit-breakers to improve sleep, and minimise anxiety. There is again no evidence to support antidepressants for the direct treatment of tinnitus.17
Novel therapies: Laser-based therapies should be strongly discouraged. No current evidence exists to recommend repetitive transcranial magnetic stimulation for the routine treatment of patients with persistent, bothersome tinnitus.20
SUMMARY
Tinnitus, in all its forms, is common, with a serious underlying cause very rare. Thorough assessment and explanation of the symptoms are very important.
It is also essential to counsel patients that there are a number of effective treatments available to manage their condition.
For those with severely intrusive tinnitus, a multidisciplinary approach is essential.
Dr Sean Flanagan is a dual fellowship trained ENT surgeon (otolaryngology head and neck surgery), sub-specialising in diseases of the ear, tumours of the skull base and in surgical correction of hearing loss including cochlear implantation and bone-anchored hearing aids. He is currently a VMO ENT Surgeon at St Vincent’s Public and Private Hospitals in Sydney, and is a conjoint lecturer at the University of NSW.
References:
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