tinnitus

tinnitus refers to the sensation of sound, most often a high-pitched, noisy whistle, in one or both ears in the absence of external stimulation. Like pain, tinnitus is a very subjective phenomenon, and descriptions by sufferers tend to be in terms of a familiar sound such as the roar of the ocean or the ringing of bells. Nearly everyone experiences a mild and transient form of tinnitus. Estimates of the incidence of more severe forms vary, but around 10–14% of adults complain of tinnitus that is either prolonged or present for much of the time, and 0.5% are so affected as to have difficulty in leading a normal life.

The first written record of tinnitus appears to date back to ancient Egyptian medical documents. There are several references in Babylonian medicine to the ‘singing ear’ or the ‘whispering ear’, for which incantation of charms was advocated. Descriptions of noises in the ear and their possible causes were placed on a more scientific footing through the works of the Greek scholar Hippocrates in the fourth and fifth centuries bc and the term tinnitus originates from ancient Rome. Over the subsequent centuries, different types of tinnitus were recognized and described more completely. However, tinnitus remains one of the least understood hearing conditions, for which there is still, in many cases, no specific cure.

Many sounds are generated within the head as a result of muscular activity and by blood rushing through the cranial vessels. However, we are rarely aware of these sounds because the cochlea is shielded by the hard temporal bone. Although people with apparently normal hearing do experience tinnitus, it usually accompanies some form of hearing loss. Indeed, most people who complain to their general practitioners of deafness will also have tinnitus. Although it is often associated with disorders of the ear itself, including blockage of the ear canal by wax, otosclerosis, and Menière's disease, it is now apparent that neural activity within the brain may be a more important factor. The discovery in the late 1970s that the ear produces sounds that can be detected in the ear canal suggested a possible link between tinnitus and the activity of outer hair cells in the cochlea. However, because drugs such as aspirin both eliminate these emissions and induce tinnitus, this seems to provide an explanation in only a few cases. Moreover, tinnitus is often found in people with severe sensorineural hearing loss or following physical damage to the inner ear, which would argue against a cochlear origin for the condition.

Because of its subjective nature and the paucity of external signs associated with tinnitus, the development of animal models has been problematic. Nevertheless, studies in animals have shown that high doses of aspirin give rise to increased spontaneous activity both in the auditory nerve fibres that leave the inner ear and in the auditory midbrain. We do not yet know the mechanisms underlying central tinnitus or even which areas of the auditory pathway are responsible, but it is possible that a change in the level of inhibitory activity may be involved.

Early remedies for tinnitus usually involved the administration, either orally or into the ear canal, of a variety of substances ranging from oils to ox urine. It was observed in ancient Greece that external noise could mask buzzing in the ears and this was used therapeutically in the nineteenth century. Unless the patient is completely deaf, noise generators are still useful today as a means of providing temporary relief. By amplifying speech or environmental noise, hearing aids can also be effective in many cases. It was claimed at the beginning of the nineteenth century that electrical stimulation of the ear could be used to treat tinnitus. In a similar vein, tinnitus is often reduced after profoundly deaf patients are fitted with a cochlear implant in which sounds are transduced into electrical signals that are delivered to electrodes inserted into the cochlea of the inner ear.

In a small minority of cases tinnitus may be alleviated if the cause of the hearing loss can be treated by surgical or medical means. Because tinnitus is aggravated by stress or fatigue, the most successful treatment involves psychological counselling or some form of relaxation therapy, often in conjunction with devices that use external noise to mask the sounds that are generated within the head.

Andrew J. King

Bibliography

Shulman, A.,, Aran, J.- M.,, Feldmann, H.,, Tonndorf, J.,, and and Vernon, J. A. (1991). Tinnitus: diagnosis/treatment. Lea and Febiger, Philadelphia.
Vesterager, V. (1997). Tinnitus — investigation and management. British Medical Journal, 314, 728–31.

See also deafness; hearing; hearing aid.