ABSTRACT: Determining whether tinnitus is objective or subjective and defining the underlying cause allows for a rational approach to therapy for this difficult-to-treat condition.
CME OBJECTIVE: The reader will understand the difference between objective and subjective tinnitus, the approach to evaluation, and options for treatment.
Benjamin M. McGrew, MD, no conflicts of interest
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Exposure to loud sounds gradually damages cochlear hair cells and results in hearing loss. The brain recognizes that the damaged ear is not generating auditory signals and sends signals through auditory pathways, which people experience as tinnitus.
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Rushing wind, roaring water, speeding trains, buzzing insects, and incessant ringing are terms individuals with tinnitus use to describe the disruptive sounds they perceive. Dating back to ancient Egypt and marching through Roman, Byzantine, medieval, and Renaissance history, tinnitus has been difficult to classify and treat (Otolaryngol Clin N Am. 2003;36:239-248). Tinnitus, however, is not a disease but the body's response to an array of conditions.
"Tinnitus is a physiological response to the absence of auditory stimulation," says UAB otolarynogological surgeon Benjamin M. McGrew, MD. This neutral description fails to convey the effect on patients' quality of life. Individuals with tinnitus can suffer from chronic depression, anxiety, fatigue, insomnia, and other debilitating side effects, he says.
About 50 million Americans experience tinnitus. Of the affected individuals, 12% have symptoms warranting medical attention, with 2 million of those experiencing incapacitating effects that limit or curtail normal function. Tinnitus is more common in adults aged 50 years and older, although the condition can affect individuals of any age. After arthritis and hypertension, hearing problems are the most common chronic complaint of older adults (JAMA. 2003;289[15]:1976-1985).
Hearing Loss and Tinnitus
Persons with tinnitus usually have experienced some degree of hearing loss, McGrew says. Bilateral hearing loss of the same degree in each ear results in bilateral tinnitus. An individual with unilateral hearing loss generally identifies the affected ear as the source of the tinnitus.
Noise-induced hearing loss (NIHL) can result from a single incident or from repeated exposure to loud sounds. Normal conversation takes place at 60 decibels (dB). Data from the National Institute of Deafness and Other Communication Disorders indicate that repeated exposure to sounds louder than 85 dB can cause NIHL. Exposure to sounds at these levels gradually damages sensitive cochlear hair cells, resulting in slow onset of NIHL and tinnitus. A single sound such as an explosion—about 120 dB—can damage hair cells enough to result in immediate NIHL and tinnitus, McGrew says.
"An individual with instantaneous hearing loss as a result of a gun shot (140 dB) may experience an abrupt onset of tinnitus. For most of these individuals, the severity of tinnitus symptoms diminishes over time. If the hearing loss is ongoing, however, individuals continue to experience tinnitus symptoms," he says.
This phenomenon relates to the neural plasticity of the brain and strongly suggests that the brain, not the ear, generates tinnitus symptoms. The brain recognizes that the damaged ear is not generating auditory signals and responds by sending signals through auditory pathways that the affected individual experiences as tinnitus.
Risk Factors
Increasingly, hearing impairment is caused by life in a noisy, technologically advanced world. Users of iPODs, MP3s, and other portable music players insert earphones directly into the ear, where the devices can generate sound levels over 85 dB. Multiple studies confirm exposure to loud music and use of personal music devices significantly increase risks for NIHL and tinnitus.
The Blue Mountain Hearing Study assessed more than 3500 adults aged 49 years and older to identify potential risks associated with tinnitus. Study results identified several factors related to tinnitus: reduced hearing and cochlear function, reported work-related noise exposure, past history of sinus or middle ear infections, severe neck injury, and migraine (Ear and Hearing. 2003;24[6]:501-507). Study authors suggest that reduction of work-related noise exposure and early intervention for otitis media may reduce development of tinnitus.
Classification, Etiology
Tinnitus is categorized into two wide-ranging forms: objective and subjective. Effective treatment depends on discernment between types. Objective tinnitus produces audible sound and is categorized by etiology and sound source. Vascular anomalies, for example, cause pulsatile tinnitus. Arteriovenous malformations, vascular tumors, or cranial hypertension can produce turbulent blood flow that creates pulsatile vascular noise. Pathological muscular and anatomic conditions such as patulous Eustachian tubes, idiopathic stapedial muscle spasms, and palatal myoclonus can cause nonvascular tinnitus.
Treatment for objective tinnitus depends on identifying and treating underlying pathology. Depending on the etiology, treatment may include embolization of blood vessels, use of mild sedatives, or injections of botulinum toxin for muscular anomalies. Objective tinnitus is not associated with hearing loss, McGrew says.
Subjective tinnitus does not produce audible external sound and is associated with measurable hearing loss. It is a pathological cognitive sensation generated in the ear, auditory nerve, or central nervous system creating phantom sound (Prog Brain Rsch. 2007;166:3-16). NIHL, presbycusis, otosclerosis, otitis media, Ménière disease, and neurological conditions such as traumatic brain injury, acoustic neuroma, and multiple sclerosis can result in subjective tinnitus. "Subjective tinnitus is not a disease for cure, but rather a physiological response to hearing loss. This symptom can often be modulated to tolerable levels by addressing the underlying physiology," McGrew says.
Diagnosis
Some forms of tinnitus are temporary and can be alleviated by medical management of causative factors. Individuals with chronic tinnitus, however, can experience long-term side effects. "The first thing patients want to know is how they developed tinnitus and how can they get rid of it," McGrew says.
A thorough clinical history, physical exam, and hearing test may reveal causal factors related to tinnitus. The chronic perception of noise can affect patients' lifestyles in many ways, and evaluation for tinnitus also requires an assessment of the impact on affected individuals. The Tinnitus Handicap Inventory measures the severity of the condition and alerts clinicians to the overarching effect of tinnitus on patients' well-being.
Intervention: Modulation or Cures?
Some tricyclic antidepressants and benzodiazepines can modulate the symptoms of tinnitus. Their efficacy for treating tinnitus varies and is related to the drug's potential anxiolytic or somnolent effects, McGrew says. Amitriptyline, nortriptyline, clonazepam, and alprazolam can offer meaningful improvements and provide relief for many patients. Cochlear implants for hearing loss also reduce tinnitus symptoms. Tinnitus masking—the use of external auditory signals from a fan, music, or white noise simulator—also may also provide effective symptomatic relief.
Lifestyle changes can help individuals cope with symptomatic tinnitus. Meditation, biofeedback, stress reduction, and avoidance of caffeine, nicotine, and alcohol may help patients eliminate tinnitus triggers. The challenge is determining which intervention works best for each patient, McGrew says.
A meta-analysis of randomized clinical trials reviewed medication, device, or intervention treatments for tinnitus. Researchers examined the efficacy of tocainide analogs, carbamazepine, gingko biloba, acupuncture, and hypnosis for relief of symptoms. The studies indicated that none of the therapies reduced tinnitus symptoms more effectively than placebo (Laryngoscope. 1999;109[8]:1202-1211).
Recent trials have examined use of gabapentin and acamprosate to treat tinnitus and have found that gabapentin effectively reduces tinnitus in some individuals with associated acoustic trauma (Laryngoscope. 2006;116 [5]:675-681). Acamprosate offered no benefit compared with placebo.
Increasing numbers of older adults developing hearing loss and tinnitus may become prime targets of unsubstantiated treatments for this chronic condition. "Tinnitus remains an annoying physiological response with no cures offering more relief than placebos, making it ripe for quackery," McGrew says.
For more information contact Dr. Benjamin McGrew at 1-800-UAB-MIST or at mist@uabmc.edu.