NORD gratefully acknowledges David J. Eisenman, MD, Associate Professor, Vice-Chairman & Residency Program Director, Chief, Division of Otology & Neurotology, Department of Otorhinolaryngology-Head & Neck Surgery, University of Maryland School of Medicine, for assistance in the preparation of this report.
Tinnitus is a common condition characterized by the perception or sensation of sound even though there is no identifiable external source for the sound. Tinnitus is often referred to as a “ringing in the ears.” However, the sounds associated with tinnitus have also been described as hissing, chirping, crickets, whooshing, or roaring sounds, amongst others, that can affect one or both ears. Tinnitus is generally broken down into two types: subjective and objective. Subjective tinnitus is very common and is defined as a sound that is audible only to the person with tinnitus. Subjective tinnitus is a purely electrochemical phenomenon and cannot be heard by an outside observer no matter how hard they try. Objective tinnitus, which is far less common, is defined as a sound that arises from an “objective” source, such as mechanical defect or a specific sound source, and can be heard by an outside observer under favorable conditions. The sounds from objective tinnitus occur somewhere within the body and reach the ears by conduction through various body tissues. Objective tinnitus is usually caused by disorders affecting the blood vessels (vascular system) or muscles (muscular system).
The majority of cases of tinnitus are subjective. Objective tinnitus is far less common. However, a diagnosis of objective tinnitus is tied to how hard and well the objective (outside) listener tries to hear the sound in question. Because of this problem, some clinicians now simply refer to tinnitus as either rhythmic or non-rhythmic. Generally, rhythmic tinnitus correlates with objective tinnitus and non-rhythmic tinnitus correlates with subjective tinnitus. Specific forms of tinnitus such as pulsatile tinnitus and muscular tinnitus, which are forms of rhythmic tinnitus, are relatively rare. Pulsatile tinnitus may also be known as pulse-synchronous tinnitus. Properly identifying and distinguishing these less common forms of tinnitus is important because the underlying cause of pulsatile or muscular tinnitus can often be identified and treated.
Individuals with tinnitus describe perceiving a wide variety of sounds including ringing, clicking, hissing, humming, chirping, buzzing, whistling, whooshing, roaring, and/or whirling. These sounds may be present at all times, or they may come and go. The volume, pitch or quality of tinnitus sounds can fluctuate as well. Some people report that their tinnitus is most obvious when outside sounds are low (i.e. during the night). Other individuals describe their tinnitus as loud even in the presence of external sounds or noise, and some describe it as exacerbated by sounds. Tinnitus can affect one ear or both ears. It can also sound like it is inside the head and not in the ears at all.
The degree of loudness or annoyance caused by tinnitus varies greatly from one individual to another. Loudness and annoyance do not always covary. An individual with loud tinnitus may not be troubled, while an individual with soft tinnitus may be debilitated. Most individuals with subjective tinnitus have hearing loss that shows up in a standard clinical audiogram. Tinnitus can sometimes worsen or sometimes improve over time.
Pulsatile tinnitus and muscular tinnitus are two forms that can be classified as rhythmic tinnitus. In pulsatile tinnitus, the characteristic sound mirrors or keeps pace (synchronizes) with a person’s heartbeat. It is rarely described as a ringing sound, but more often as a whooshing, pulsing, or screeching sound.
In muscular tinnitus, the sound is often described as a “clicking” noise and is usually associated with myoclonus affecting muscles near – or in – the ear. Myoclonus is an involuntary spasm or jerking of a muscle or group of muscles caused by abnormal muscular contractions and relaxations.
There are numerous, varied causes of non-rhythmic tinnitus, the most common of which are hearing loss and/or noise exposure. Rhythmic tinnitus is usually caused by disorders affecting the blood vessels (vascular system) or muscles (muscular system).
Pulsatile tinnitus is generally caused by abnormalities or disorders affecting the blood vessels (vascular disorders), especially the blood vessels near or around the ears. Such abnormalities or disorders can cause a change in the blood flow through the affected blood vessels. The blood vessels could be weakened from damage caused by hardening of the arteries (atherosclerosis). For example, abnormalities affecting the carotid artery, the main artery serving the brain, can be associated with pulsatile tinnitus. A rare cause of pulsatile tinnitus is a disorder known as fibromuscular dysplasia (FMD), a condition characterized by abnormal development of the arterial wall. When the carotid artery is affected by FMD, pulsatile tinnitus can develop.
It is possible that the most common cause of pulsatile tinnitus is sigmoid sinus diverticulum and dehiscence, which can be collectively referred to as sinus wall abnormalities or SSWA. The sigmoid sinus is a blood carrying channel on the side of the brain that receives blood from veins within the brain. The blood eventually exits through the internal jugular vein. Sigmoid sinus diverticulum refers to the formation of small sac-like pouches (diverticula) that protrude through the wall of the sigmoid sinus into the mastoid bone behind the ear. Dehiscence refers to absence of part of the bone that surrounds the sigmoid sinus in the mastoid. It is unknown whether these conditions represent different parts of one disease process or spectrum, or whether they are two distinct conditions. These abnormalities cause pressure, blood flow, and noise changes within the sigmoid sinus, which ultimately results in pulsatile tinnitus. Narrowing of the blood vessel that leads into the sigmoid sinus, known as the transverse sinus, has also been associated with pulsatile tinnitus.
Superior semicircular canal dehiscence syndrome is another not uncommon cause of pulsatile tinnitus. The superior semicircular canal is one of three canals found in the vestibular apparatus of the inner ear. The vestibular apparatus helps to maintain equilibrium and balance. In this syndrome, a part of the temporal bone that overlies the superior semicircular canal is abnormally thin or absent. Superior semicircular canal dehiscence syndrome can affect both hearing and balance to different degrees.
Additional conditions that can cause pulsatile tinnitus include arterial bruit, abnormal passages or connections between the blood vessels of the outermost layer of the membrane (dura) that covers the brain and spinal cord (dural arteriovenous shunts), or conditions that cause increased pressure within the skull such as idiopathic intracranial hypertension (pseudotumor cerebri). Sigmoid sinus dehiscence may be associated with pseudotumor, but this connection has not been firmly established. It possible that cases of pulsatile tinnitus associated with pseudotumor may be caused by an undiagnosed SSWA. Head trauma, surgery, middle ear conductive hearing loss, and certain tumors can also cause pulsatile tinnitus. Obstructions within in the vessels that connect the heart and brain can also cause pulsatile tinnitus.
Muscular tinnitus can be caused by several degenerative diseases that affect the head and neck including amyotrophic lateral sclerosis or multiple sclerosis. Myoclonus can also cause muscular tinnitus, especially palatal myoclonus, which is characterized by abnormal contractions of the muscles of the roof of the mouth. Spasms of the stapedial muscle (which attaches to the stapes bone or stirrup), which is the smallest muscle in the body, and tensor tympani muscle, both of which are located in the middle ear, have also been associated with objective tinnitus. Myoclonus or muscle spasms may be caused by an underlying disorder such as a tumor, tissue death caused by lack of oxygen (infarction), or degenerative disease, but it is most commonly a benign and self-limiting problem.
Patulous Eustachian tubes can be associated with tinnitus. The Eustachian tube is a small canal that connects the middle ear to the back of the nose and upper throat. The Eustachian tube normally remains closed. In individuals with a patulous Eustachian tube, the tube is abnormally open. Consequently, talking, chewing, swallowing and other similar actions can cause vibrations directly onto the ear drum. For example, affected individuals may hear blowing sounds that are synchronized with breathing.
Tinnitus affects males and females in equal numbers. It can affect individuals of any age, even children. Tinnitus, collectively, is a very common condition and estimated to affect approximately 10% of the general population. Rhythmic tinnitus occurs far less frequently than non-rhythmic tinnitus, accounting for approximately 1% of all cases of tinnitus and is considered relatively rare in the general population. The exact prevalence or incidence of rhythmic tinnitus is unknown. Rhythmic tinnitus due to pseudotumor and sinus wall anomalies is found most commonly in overweight women in their 3rd to 6th decade of life. The onset of tinnitus can be abrupt or develop slowly over time.
A diagnosis of tinnitus is based upon identification of characteristic symptoms, a detailed patient history, a thorough clinical evaluation and complete audiologic testing. These steps will help to differentiate rhythmic tinnitus from non-rhythmic tinnitus. It cannot be overemphasized that tinnitus is a symptom of another underlying condition and not a diagnosis in and of itself. Because of the high number of underlying causes of tinnitus, a variety of specialized tests to detect the specific cause may be necessary. Attempting to identify the underlying cause of tinnitus is the first step in evaluating a person with tinnitus.
Clinical Testing and Workup
Affected individuals will first undergo a medical evaluation beginning with a hearing test (audiogram). An individual with tinnitus may also be asked to perform a series of movements including clenching one’s jaw or moving one’s neck or eyes. If these movements cause tinnitus to change, it can help a physician figure out the underlying cause.
A diagnosis of rhythmic tinnitus may require a series of diagnostic tests in order to pinpoint the specific cause. The specific tests performed will vary for each individual case, based, in part, on the results of the initial medical evaluation.
Generally, following the initial evaluation, individuals suspected of rhythmic tinnitus will undergo some form of specialized medical imaging. Individuals may undergo high resolution computed tomography (HRCT) or magnetic resonance angiography (MRA) to evaluate blood vessel abnormalities such as a vascular malformation that may be the cause of tinnitus. An HRCT scan can also be used to evaluate the temporal bone for sinus wall abnormalities and superior semicircular canal dehiscence. HRCT uses a narrow x-ray beam and advanced computer analysis to create highly detailed images of structures within the body such as blood vessels. An MRA is done with the same equipment use for magnetic resonance imaging (MRI). An MRI uses a magnetic field and radio waves to produce cross-sectional images of particular structures or tissues within the body. An MRA provides detailed information about blood vessels. In some cases, before the scan, an intravenous line is inserted into a vein to release a special dye (contrast). This contrast highlights the blood vessels, thereby enhancing the results of the scan.
These tests are usually performed instead of a traditional catheter angiography, which is more invasive and, while generally very safe, carries greater risk of complications. Angiography is an imaging technique that involves injecting dye into a small tube called a catheter that has been inserted into a blood vessel. An x-ray is then performed to assess the health of the vessels as well as the rate of blood flow.
An ultrasound is another test that may be used to aid in the diagnosis of tinnitus. An ultrasound uses reflected high-frequency sound waves and their echoes to create images of structures within the body. An ultrasound can reveal how blood flows within vessels, but is only useful for accessible vessels. It is not helpful for blood vessels within the skull.
A variety of additional tests may be performed to rule out other potential conditions or underlying causes of tinnitus depending upon the specifics of each individual case.
Because the most common cause of non-rhythmic tinnitus is hearing loss, the initial treatment in most cases is hearing rehabilitation with either hearing aids or surgery depending upon the specific cause.
In some cases, a special audiologic device, which is worn like a hearing aid, may be prescribed. These devices, called masking agents, emit continuous, low-level white noises that suppress the tinnitus sounds. In some cases, a hearing aid may be recommended to help to suppress or diminish the sounds associated with tinnitus. A combination device (masker plus hearing aid) may also be used. Masking devices provide immediate relief by reducing or completely drowning out the tinnitus sound. However, when the masking device is removed, the tinnitus sound remains.
Tinnitus habituation therapies, such as tinnitus retraining therapy (TRT), involve using low level sounds in a graduated fashion to decrease the perception of tinnitus. This differs from use of masking devices such as described earlier. TRT involves a wearable device that an affected individual can adjust so that the level of sound emitting from the device is about equal to or matches the tinnitus sound. This may be called the “mixing point” because the sound from the device and the tinnitus sound begin to mix together. An affected individual must repeatedly adjust the device so that the sound is at or just below the mixing point. TRT is supported by counseling with a trained professional who can teach the individual the proper techniques to maximize the effectiveness of TRT. Eventually, by following this method, affected individuals no longer need the external sound generating device. Affected individuals will become accustomed to the tinnitus sound (habituation), except when they choose to focus on it. Even then the sound will not be bothersome or troubling. The theory is akin to a person’s ability to ignore sounds such as the hum of air conditioner, the refrigerator motor turning on, or raindrops falling on the roof when driving a car in the rain.
Some people with tinnitus may obtain relief by listening to background sounds that they find pleasant (e.g. ocean surf).
Treatment of the underlying primary disorder may help to improve or cure rhythmic tinnitus. For example, the treatment of blood vessel disorders (e.g. dural arteriovenous shunts) can include certain medications or surgery. A surgical procedure known as sinus wall reconstruction can successfully treat pulsatile tinnitus due to sigmoid sinus diverticulum and dehiscence. In fact, most individuals have experienced complete resolution of their tinnitus following this surgery. Surgery may also be necessary for rare cases of pulsatile tinnitus caused by a tumor.
Muscular tinnitus may go away without treatment. If the sound persists, drugs that relax the muscles (muscle relaxants) may be tried. In some cases, surgery may be necessary.
Individuals with rhythmic tinnitus without an identified cause may be treated by masking devices or TRT or other habituation techniques as described above.
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