Article Published in the Author Account of

Yvonne Chan

Tinnitus: Etiology, Classification, Characteristics, and Treatment

Abstract: Tinnitus is the perception of sound with the absence of acoustic stimulus. It affects approximately 10% of the population. This is a symptom with a broad differential diagnosis. In some cases, tinnitus impacts significantly on patients' activities of daily living. Understanding how to differentiate between subjective and objective tinnitus is essential to the evaluation and management of these patients. The various causes of each type of tinnitus will be discussed. This review presents a general approach to tinnitus in order to facilitate timely diagnosis and management of this complex symptom.



Introduction

The term “tinnitus” is derived from the Latin word “tinnire,” meaning “to ring.” Tinnitus is the perception of sound in the head or the ears in the absence of an external source. The American Tinnitus Association estimates that 50 million people in the United States suffer from chronic tinnitus (American Tinnitus Association, 2009). A U.K. study involving 48,313 subjects reported a 10.1% prevalence of tinnitus in the adult population (Davis and Rafaie, 2000), which increases with age (Ahmad and Seidman, 2004). Tinnitus has been found to affect more men than women (Lockwood et al., 2002). The impact of tinnitus can be significant enough to interfere with activities of daily living. Approximately 25% of patients with tinnitus report an increase in severity over time (Stouffer and Tyler, 1990). Tinnitus is a symptom of a wide variety of disease processes. It is most commonly associated with hearing loss; however, it may be the presenting symptom of a vascular or neurologic disorder. This review discusses the classification, causes, diagnosis, and management of tinnitus.

Classification and Characteristics of Tinnitus

Tinnitus can be divided into two broad categories, subjective and objective tinnitus. Objective tinnitus is sound generated somewhere in the body and reaches the ear through conduction in body tissues. It is audible to anyone in addition to the affected individual. On the other hand, subjective tinnitus is sound not associated with a physical noise and is only audible to the affected individual. The severity of sounds perceived by individuals with tinnitus can range from a quiet background noise to loud noise overpowering external sounds.

Objective tinnitus, sometimes referred to as somatic tinnitus, is rare and is caused by a mechanical sound in the body. These sounds are often generated by muscular structures or vascular structures in the head and neck area. Objective tinnitus can be further subdivided into 3 groups, namely, pulsatile, muscular, and spontaneous (Lockwood et al., 2002). Pulsatile tinnitus is usually caused by sounds caused by turbulent blood flow that may be in sync with the cardiac cycle. Muscular tinnitus is often described as a “clicking” noise and is most commonly due to palatal myoclonus or contractions of the tensor tympani or stapedius muscles (Lockwood et al., 2002). Spontaneous tinnitus has been linked to vibrations of the outer hair cells of the cochlea known as spontaneous otoacoustic emissions (Penner, 1992).

Subjective tinnitus is the perception of sound without any auditory stimulus. Many people experience transient tinnitus lasting seconds or minutes after exposure to loud noise. In a group of tinnitus patients, 22% reported equal sounds in both ears, 34% reported experiencing unilateral sounds (Stouffer and Tyler, 1990). The sounds associated with subjective tinnitus have been described as ringing, hissing, water running, humming, crickets, cicadas, whistling, wind blowing, etc (Stouffer and Tyler, 1990). Most patients experience a high pitch noise typically above 3,000Hz (Henry et al., 1984).

Etiology of Tinnitus

Objective Tinnitus

Pulsatile tinnitus is most often associated with a number of different vascular etiologies, including arterial bruit, dural arteriovenous shunts, paraganglioma, and venous hum. Arterial bruits may be present in arteries near the temporal bone, most commonly the pertrous carotid system (Fortune et al., 1999). Dural ateriovenous shunts represent another source of pulsatile tinnitus. Paraganglioma is a vascular neoplasm arising from paraganglia cells at the carotid bifurcation, in the jugular bulb, or along tympanic arteries. These neoplasms may generate pulsating sounds that are transmitted to the cochlea and produce objective tinnitus. Venous hums may be heard in patients with a dehiscent jugular bulb, systemic hypertension, or increased intracranial pressure.

Muscular tinnitus may be a result of spasms of the muscles of the middle ear, namely, the tensor tympani and the stapedius muscles. Myoclonus of the palatal muscles may be the cause of clicking noises, which may be indicative of an underlying neurologic disorder, such as multiple sclerosis or neuropathy. Another somatic disorder such as Eustachian tube dysfunction may cause tinnitus that is synchronous with respiratory movements (Liyanage et al., 2006).

Subjective Tinnitus

Subjective tinnitus is a symptom of a number of different underlying pathophysiologic processes. Causes of subjective tinnitus include otologic, neurologic, infectious, and drug-related (Lockwood et al., 2002). Otologic cause is the most common cause of subjective tinnitus. These include noise-induced hearing loss, presbycusis, otosclerosis, otitis, cerumen impaction, Meniere’s disease, and sudden sensorineural hearing loss. Neurologic etiologies include head injury, whiplash, multiple sclerosis, vestibular schwannoma, and other cerebellopontine-angle tumors. Tinnitus may arise as a result of a number of infectious sources such as otitis media, Lyme disease, meningitis, or syphilis. Medications also constitute a common cause of subjective tinnitus. Most commonly implicated drugs include salicylates, non-steroidal anti-inflammatory medication, aminoglycocide antibiotics, loop diuretics, and chemotherapy agents.

Approach to Tinnitus

Due to the vast array of possible underlying diagnoses, careful evaluation of each patient who presents with tinnitus is warranted. The first crucial step in the management of tinnitus is to distinguish between subjective and objective tinnitus, which is achieved through a complete history and physical examination.

Characterization of the sound in terms of its exact description, onset, periodicity, frequency, triggers, and associated symptoms are crucial. Other otologic complaints such as hearing loss, aural fullness, and vertigo should be documented. Triggers such as background noise, stress, or sleeplessness should be specifically questioned. History of noise exposure, head injury, and otitis media needs to be explored. Possible ototoxic medications should be enquired. In addition to a meticulous history, another important component is the patient’s psychological state.

A complete head and neck examination should be performed including otologic and neurotologic evaluations. Specific attention should be directed at auscultation of periauricular area, observation of palatal movements, and changes of tinnitus with jaw clenching or eye movements. A comprehensive audiologic assessment including puretone thresholds, acoustic impedance, speech discrimination scores, and acoustic reflex threshold, should be performed.

Specialized testing may be necessary in certain cases of tinnitus. For objective tinnitus that is pulsatile, it is prudent to rule out any life-threatening diseases such as dural arteriovenous malformation, aneurysm, or skull base tumor. These lesions can be diagnosed with MR angiography or CT angiography (Dietz et al., 1994). Skull base tumor such as paraganglioma can be evaluated by CT temporal bones. MRI can diagnose central nervous system tumors, cerebellopontine angle tumors, increased intracranial pressures, and multiple sclerosis.

Treatment

Once a serious medical condition has been ruled out, the treatment of tinnitus should be aimed at symptom relief. Approximately 10% of patients with tinnitus have severe symptomatology which interferes with their quality of life (Ahmad and Seidman, 2004). Since tinnitus is a chronic condition in most patients, the goals of management are twofold, to reduce the intensity of tinnitus and to decrease its impact and associated disability. Reassurance in patients with benign etiologies of tinnitus is often helpful for patients.

Pharmacotherapy

A number of medications have been studied in the treatment of tinnitus, however, only a small number including Nortriptyline, Amitriptyline, Alprazolam, Clonazepam, and Oxazepam demonstrated limited benefits over placebo (Dobie, 1999). The use of these medications for tinnitus treatment should be cautioned. The studies with Gabapentin are inconclusive; one demonstrated improved scores of annoyance from tinnitus but a variable effect on tinnitus loudness in patients with tinnitus due to trauma specifically (Bauer and Brozoski, 2006). Another study found that it was ineffective with severe idiopathic tinnitus (Piccirillo et al., 2007). Intravenous lidocaine has demonstrated short-term improvement in patients with low-pitched tinnitus (Murai et al., 1992); unfortunately, lidocaine cannot be used clinically since it is an injection with short duration effects. Intratympanic injection of Dexamethasone has been shown to be effective in some cases of idiopathic tinnitus such as sudden sensorineural hearing loss or autoimmune inner ear disease (Slattery et al., 2005).

Behavioral Therapy

Non-medicinal treatments that have been studied with some success include the following: (1) Tinnitus retraining therapy, (2) Masking, (3) Biofeedback and stress reduction programs, and (4) Cognitive behavioral therapy.

Tinnitus retraining therapy (TRT) aims to bypass or override abnormal auditory cortex neural connections. TRT involves facilitating habituation to the tinnitus signal by a combination of retraining counseling and sound therapy with broad band noise as well as environmental sounds (Han et al., 2009). The long term impact of TRT is limited (Dobie, 1999) and it can take up to one to two years to observe stable effects. Masking devices are designed to produce low level sounds to help eliminate the perception of tinnitus (Vernon and Meikle, 2003). For patients with hearing loss, a hearing aid is a form of sound therapy to divert the patient’s attention from tinnitus to the amplified speech or ambient noise (Han et al., 2009). Biofeedback is a relaxation technique that aims to help patient manage tinnitus-related distress by changing the patient’s reaction to it (Andersson and Lyttkens, 1999). Cognitive behavioral therapy (CBT) in the setting of tinnitus teaches patients to alter their psychological response to the symptom by learning coping strategies and distraction skills. Studies have demonstrated that CBT helped patients reduce tinnitus related distress (Zachriat and Kroner-Herwig, 2004).

Summary

Tinnitus is the presenting symptom for a number of different diseases ranging from benign to life-threatening conditions. As a clinician, one should differentiate between subjective and objective tinnitus in order to formulate further testing and make appropriate recommendations in terms of management. Even with the recent medical advances, no treatment has been found to be uniformly effective in the treatment of tinnitus. It is prudent to deal with each patient individually and discuss the risks and benefits of each treatment option through a strong doctor-patient relationship.

References

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[Discovery Medicine, 8(42):133-136, October 2009]

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