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Tinnitus (pronounced /t?’na?t?s/ or /’t?n?t?s/,[1] from the Latin word for “ringing”[2]) is the perception of sound within the human ear in the absence of corresponding external sound.
Tinnitus can be perceived in one or both ears or in the head. It is usually described as a ringing noise, but in some patients it takes the form of a high pitched whining, buzzing, hissing, humming, or whistling sound, or as ticking, clicking, roaring, “crickets” or “tree frogs” or “locusts”, tunes, songs, or beeping.[3] It has also been described as a “wooshing” sound, as of wind or waves.[4]. Tinnitus can be intermittent or it can be continuous. In the latter case, this “phantom” sound can create great distress in the sufferer.
Tinnitus is not itself a disease but a symptom resulting from a range of underlying causes. Causes include ear infections, foreign objects or wax in the ear, nose allergies that prevent (or induce) fluid drain and cause wax build-up, and injury from loud noises. Tinnitus is also a side-effect of some oral medications, such as aspirin, and may also result from an abnormally low level of serotonin activity. It is also a classical side effect of Quinidine, a Class IA anti-arrhythmic. In many cases, however, no underlying physical cause can be identified.
The sound perceived may range from a quiet background noise to one that can be heard even over loud external sounds. The term “tinnitus” usually refers to more severe cases. Heller and Bergman (1953) conducted a study of 80 tinnitus-free university students placed in an anechoic chamber and found that 93% reported hearing a buzzing, pulsing or whistling sound. Cohort studies have demonstrated that damage to hearing (among other health effects) from unnatural levels of noise exposure is very widespread in industrialized countries.[5]
Because tinnitus is often defined as a subjective phenomenon, it is difficult to measure using objective tests, such as by comparison with noise of known frequency and intensity, as in an audiometric test. The condition is often rated clinically on a simple scale from “slight” to “catastrophic” according to the practical difficulties it imposes, such as interference with sleep, quiet activities, and normal daily activities.[6] For research purposes, the more elaborate Tinnitus Handicap Inventory is often used.[4][7]
In some cases, a clinician can perceive an actual sound (e.g., a bruit) emanating from the patient’s ears. This is called objective tinnitus. Objective tinnitus can arise from muscle spasms that cause clicks or crackling around the middle ear.[8] Some people experience a sound that beats in time with the pulse (pulsatile tinnitus).[9] Pulsatile tinnitus is usually objective in nature, resulting from altered blood flow or increased blood turbulence near the ear (such as from atherosclerosis or venous hum[10]), but it can also arise as a subjective phenomenon from an increased awareness of blood flow in the ear.[9] Rarely, pulsatile tinnitus may be a symptom of potentially life-threatening conditions such as carotid artery aneurysm[11] or carotid artery dissection.[12]
The basis of quantitative measurement of tinnitus relies on the brain’s tendency to select out only the loudest sounds heard. Based on this tendency, the amplitude of a patient’s tinnitus can be measured by playing sample sounds of known amplitude and asking the patient which he or she hears. The tinnitus will always be equal to or less than sample noises heard by the patient. This method works very well to gauge objective tinnitus (see above.) For example: if a patient has a pulsatile paraganglioma in his ear, he will not be able to hear the blood flow through the tumor when the sample noise is 5 decibels louder than the noise produced by the blood. As sound amplitude is gradually decreased, the tinnitus will become audible, and the level at which it does so provides an estimate of the amplitude of the objective tinnitus.
Objective tinnitus, however, is quite uncommon. Often patients with pulsatile tumors will report other coexistent sounds, distinct from the pulsatile noise, that will persist even after their tumor has been removed. This is generally subjective tinnitus, which, unlike the objective form, cannot be tested by comparative methods.
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