Tinnitus and Perception of Sounds
Tinnitus is the perception of sounds in the head or the ears. The term tinnitus derives from the Latin word tinnire, meaning to ring. Typically, an individual perceives the sound in the absence of outside sounds, and the perception is unrelated to any external source. Sound that only the patient hears is subjective tinnitus, while sound that others can hear as well is called objective tinnitus. Estimates of patients with tinnitus range from 10-15% of the population (30-40 million people). Of patients presenting with ear-related symptoms, 85% report experiencing tinnitus as well. Both adults and children report experiencing tinnitus. Development of tinnitus increases in incidence with age, although the rate of tinnitus in children has been reported as high as 13%.
Many people experience tinnitus after exposure to a gunshot or a loud concert with modern amplification. This type of tinnitus can be annoying, but it usually resolves in a matter of hours. Tinnitus is a symptom (not a disease) and therefore reflects an underlying abnormality. Most typically, tinnitus is associated with a sensorineural hearing loss, but tinnitus types such as pulsatile tinnitus, tinnitus with vertigo, fluctuating tinnitus, or unilateral tinnitus should be investigated thoroughly.
Most of the knowledge and therapeutic options available to those who experience tinnitus have been encapsulated above. Individuals have placed advertisements in major otolaryngology, audiology, and neurology journals seeking therapeutic help. Such advertisements have yielded a great deal of interest but little substantive therapy. Unfortunately, because so little is known about the causes of tinnitus, little therapy is available to eliminate the problem. Frequently, therapy that is helpful to one person is not helpful to the next. Thus, many have adopted the philosophical outlook that tinnitus is a chronic or psychologic disease and is managed and not cured.
That philosophic approach to the problem of chronic tinnitus is apparent throughout this discussion of tinnitus. Because so few patients are cured, the emphasis should be on helping each individual cope with what is likely to be a chronic problem. As always, areas of active research are focused on developing a better understanding and therapy of tinnitus, and these are of importance for those interested in academic or investigative pursuits.
Such investigations have recently focused around the quantification of tinnitus, the medical and legal aspects of the problem, and the source of tinnitus. Many of these treatments are pioneered by a dedicated few. Most are described in a journal committed to the investigation, understanding, and treatment of tinnitus.
Tinnitus is classified in many cases into 2 categories. Tinnitus is either objective (ie, audible to anyone in addition to the affected individual) or subjective (ie, audible only to the affected individual). Even though this classification system is used quite frequently, focusing on the etiology of tinnitus is often more useful. The classification is discussed, and then this article focuses primarily on the various etiologies of tinnitus and their respective therapies.
Objective tinnitus is relatively rare. It is sound created somewhere in the body, usually in the ear, head, or neck, and has a muscular or vascular etiology. Muscular tinnitus is observed in several degenerative diseases of the head and neck, including amyotrophic lateral sclerosis. In this entity, the neuromuscular control over the muscles in the ear occasionally deteriorates in an individual with perfect sensory perception. Occasionally, the loss of control results in a repetitive flutter or myoclonus of either the stapedius or tensor tympani muscles. The result is an observable and audible flutter coming from the ear.
Lysis of the tensor or stapedius muscle via a tympanotomy incision is uniformly successful in relieving the symptoms in these cases. However, attention must be paid to the contralateral side. Often, the problem is bilateral, but attention is directed to the louder side. If in fact contralateral problems are present, both muscles should be cut at the same time. This is one of the few cases in otology where operating on both sides at the same time may be considered, decreasing the anesthesia risk and attendant logistic problems for the patient who frequently has problems with anxiety.
Palatal myoclonus is a rare cause of muscular-induced clicking tinnitus. It results from rhythmic discharges from the inferior olivary nucleus by a lesion in the triangle of the Guillain-Mollaret (brainstem). The lesion is usually due to stroke, trauma, encephalitis, multiple sclerosis (MS), or degenerative disease. Some success has been reported with botulinum toxin injection therapy.
The other disturbance that is more frequently observed is an aberrance or abnormality of the carotid artery. Aberrances of the carotid artery are documented multiple times in the literature. The carotid artery can also become ectatic as a person ages or as operations are performed on the carotid. The end result is an artery that often takes a tortuous route through the neck and the ear to reach the brain. Such tortuosity produces turbulent flow in the artery, which can be auscultated by the examiner with each heartbeat.
Similarly, the jugular bulb and the jugular vein can produce a type of tinnitus that is characterized as a venous hum. Often described by the patient as a vibration or a low-pitched sound rather than as a ringing, these sounds seem to be slightly more frequent than the other 2 types of objective tinnitus. Many operations have been described for the treatment of venous hum tinnitus and carotid arterial tinnitus all of these operations have initially met with success but limited long-term control of the symptom.
Clinically, subjective tinnitus is the perception of sound in the absence of auditory stimulation. In terms of neurophysiology, tinnitus is the consequence of the brain’s response to input deprivation from the auditory periphery. In the healthy auditory system, there is an ordered tonotopic frequency mapping from the auditory periphery (cochlea), through the midbrain, to the auditory cortex. When a region of the cochlea is damaged, the subcortical and cortical projections adjust to this chronic lack of output (plasticity), and the tonotopic organization is altered. In the auditory cortex, the region that corresponds to the area of cochlear damage is termed the lesion projection zone (LPZ). After cochlear damage, neurons in the LPZ show 2 important changes: an increase in the spontaneous firing rate and an increase in the frequency representation of the neurons that border the region of damage (the so-called lesion edge frequencies).
These findings are explained in terms of a) the loss of central inhibition on the regions that are damaged and b) cortical plasticity of the neighboring regions of the cortex that are still active. Hence, tinnitus neurophysiology is related to detrimental cortical adaptation to input deprivation from the sensory periphery.
Additional data from animal and human studies have suggested that tinnitus may be associated with neuronal hyperactivity at different levels of the central auditory pathways, including the dorsal cochlear nucleus, the inferior colliculus, auditory cortex, and the striatum.
A literature review, by Tegg-Quinn et al, indicated that tinnitus can cause cognitive difficulties in adults by affecting executive control of attention.
Measurement and quantification
Volumes are devoted to the quantification and measurement of tinnitus. One of the more successful and useful mechanisms for the quantification of tinnitus has been the matching of tinnitus to a tone presented to the patient in a sound-treated room, using an audiometer. Such procedures, types of tinnitus matching, are used to provide a measure of tinnitus for reevaluation of symptoms before, during, and after therapy. Although those who experience tinnitus often describe their match as exact, they quickly point out that such a match does not adequately reflect the severity of the problem affecting their daily lives.
Tinnitus is a symptom that requires further investigation to determine origin. Often, the origin may be a sensorineural hearing loss. Certain types of tinnitus signify other problems. Unilateral or pulsatile tinnitus and tinnitus associated with vertigo or conductive hearing losses are examples. Tinnitus therapy is as multifaceted as the origins of tinnitus. Choose therapy, therefore, with individual symptoms and problems in mind. A combination of sound-based therapy with medical therapy of anxiety, depression, or insomnia will help most patients. By applying the best of the multiplicity of available therapies, patients need never again hear the old adage, “you’ll just have to live with it.”
Moller AR. Sensorineural Tinnitus: Its Pathology and Probable Therapies. Int J Otolaryngol. 2016. 2016:2830157.
Tegg-Quinn S, Bennett RJ, Eikelboom RH, Baguley DM. The impact of tinnitus upon cognition in adults: a systematic review. Int J Audiol. 2016 May 31. 1-8.
Bhatt JM, Bhattacharyya N, Lin HW. Relationships between tinnitus and the prevalence of anxiety and depression. Laryngoscope. 2017 Feb. 127 (2):466-9.
Kim HJ, Lee HJ, An SY, et al. Analysis of the prevalence and associated risk factors of tinnitus in adults. PLoS One. 2015. 10 (5):e0127578.
Yang P, Ma W, Zheng Y, Yang H, Lin H. A Systematic Review and Meta-Analysis on the Association between Hypertension and Tinnitus. Int J Hypertens. 2015. 2015:583493.
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