What is Tinnitus?
Tinnitus is the perception of sound with no external source. It may be intermittent or constant, mild or severe, and vary from a low roar to a high-pitched ringing. It may be subjective (audible only to the patient) or objective (audible to others). It may or may not be associated with hearing impairment. Tinnitus must always be thought of as a symptom and not a disease, just as pain in the arm or leg is a symptom and not a disease. Because the function of the auditory (hearing) nerve is to carry sound, the brain interprets any irritation or impulse from the nerve as noise. This phenomenon is similar to the sensation nerves elsewhere in the body.
What are some of the causes of tinnitus?
In order to understand the possible causes of tinnitus, one must have some knowledge of the hearing mechanism. This mechanism is made up of five main divisions: the external ear, the middle ear, the inner ear, the nerve pathways, and the brain.
The external ear consists of the auricle and the external ear canal. These structures collect the sound waves and transmit them to the eardrum.
The middle ear lies between the eardrum and the inner ear. This chamber contains three ossicles (hearing bones): the malleus, the incus and the stapes (hammer, anvil and stirrup). Vibrations of the eardrum are transmitted across the middle ear space by these three small ear bones. Movement of the third bone (stapes or stirrup) results in fluid waves in the inner ear.
The inner ear is enclosed in dense bone and contains fluid and the tiny hearing cells. It is lined by a delicate transparent membrane supplied by microscopic blood vessels. In this small chamber, fluid waves resulting from movement of the stapes are transformed into electrical impulses in the hearing nerve.
The electrical impulses created in the inner ear chamber are transmitted to the brain by the hearing nerve. The nerve pathways leading to the brain are enclosed in a small bony canal along with the nerve responsible for balance and the nerve which stimulates movement of the facial muscles.
The hearing nerve pathways divide as they reach the brain into an inter-communicating system far more complex than the most extensive telephone exchange. Nerve impulses are then transformed into recognizable sound.
Most tinnitus is audible only to the patient; this is called subjective tinnitus. Tinnitus audible to both the patient and others is called objective tinnitus and is much less common. Among other causes, objective tinnitus may be due to muscle spasms in the middle ear or Eustachian tube, or may be due to abnormalities in the blood vessels surrounding the ear.
Tinnitus may result from spasm of one of the two muscles attached to the middle ear bones, or from spasm of muscles attached to the Eustachian tube. These muscles may begin to contract for brief periods of time, leading to a repetitious sound in the ear, often described as a clicking. Should the muscles spasm continue, medical treatment may be necessary.
There are two large blood vessels intimately associated with the middle and inner ear: the jugular vein and the carotid artery. These are the major blood vessels supplying the brain.
It is not uncommon to hear one’s heartbeat or to hear the blood circulating through these large vessels. This may be noticeable when an individual has a fever, a middle ear infection, or after engaging in strenuous exercise. This circulation increase is temporary and usually subsides when the exertion or fever are reduced. It is not audible to others.
On occasion, the sound of blood circulation will become audible to others. This can be due to thickening of the blood vessel wall (a normal occurrence as one grows older), a kink in the vessel, or an abnormal growth on the vessel wall. Other causes are possible and further testing may be necessary to determine the exact cause and treatment indicated in these uncommon cases.
External Ear Tinnitus
Obstruction of the external ear canal by wax, foreign bodies, or swelling may produce a hearing impairment or pressure on the eardrum. This frequently results in a pulsating type of tinnitus.
Middle Ear Tinnitus
Disturbances of function of the middle ear may result from allergy, infection, injury, scar tissue, or impaired motion of the three middle ear bones. These disturbances often result in hearing impairment and may cause tinnitus.
Inner Ear Tinnitus
Any condition which disturbs the fluid pressure in the inner ear chamber may produce tinnitus. This may be due to infection, allergy, or circulatory disturbances which produce changes not only in the fluid, but also in the encasing membranes of the inner ear.
Nerve Pathways Tinnitus
The hair cells and nerve pathways are the most delicate structures of the hearing mechanism. The slightest interference with these cells can impair functions. This may occur from a variety of causes: infection, systemic diseases, sudden or prolonged noise exposure, drug exposure, and even subtle changes in blood supply.
After reviewing the many causes of this symptom, it is easy to understand why the hearing may at times be affected when tinnitus is present. In fact, 90% of people who report experiencing tinnitus also have a hearing impairment. If a hearing loss coexists with tinnitus, the severity of the noise is not an index as to the future course of the hearing impairment.
Stress and Depression
Stress, physical or emotional, is present in everyone’s life periodically. In some it is chronic, and can result in symptoms or lead to depression. At times, a symptom such as tinnitus may in itself lead to depression and this can then make the tinnitus more bothersome; a vicious circle develops. Knowing this, we may recommend that a patient with severe tinnitus be treated with antidepressants or anti-anxiety medications, often under the care of a specialist. Patients of this type are also the ones who are most likely to benefit from biofeedback treatment.