tinnitus

   Also known as tinnitus aurium and syrigmus. The term tinnitus comes from the Latin verb tinnire, which means to ring. The person credited with its introduction is the Roman natural philosopher Gaius Plinius Secundus, better known as Pliny the Elder (AD 23-79). Tinnitus has been variously designated as 'ringing in the ears', 'phantom sounds', the perception of a sound in the absence of external auditory stimulation, and the perception of elementary non-environmental sounds or noise in the ear. Phe-nomenologically, it may present in the form of a variety of "akoasms (i.e. "nonverbal auditory hallucinations) such as ringing, hissing, a clear tone, a high-tension wire, buzzing, sizzling, whistling, humming, ticking, clicking, pounding, roaring, a pulsating sound, the sound of the wind or waves upon the shore, an ocean roar, and the chirping of crickets. When tinnitus is characterized by a single tone, it is referred to as "tonal tinnitus. When characterized by a band of noise rather than a single tone, the term employed is " noise-type tinnitus. Using the degree of coherence of binaural sounds as a guiding principle, tinnitus has been divided into " coherent tinnitus (characterized by a single, centred, auditory percept), and " incoherent tinnitus (characterized by two distinct stimuli). Sometimes tunes and songs are also identified as tinnitus (i.e. "musical tinnitus), especially when they develop out of a more amorphous sound, such as ringing, buzzing or humming. Phenomenologically, musical tinnitus is indistinguishable from "musical hallucinations. Tinnitus in general may be experienced either monoaurally, binaurally, or as a sound perceived 'inside the head'. The perceived noise level may range from a quiet background noise to a signal that is loud enough to drown out all other sounds. The lifetime prevalence of tinnitus is estimated at between 10 and 15%, and that of severe, chronic tinnitus at between 2 and 5%. Using the scope of the perceived sound as a guiding principle, tinnitus has been divided into " subjective and " objective tinnitus. The term subjective tinnitus refers to a type of tinnitus which is experienced solely by the affected individual. The term objective tinnitus is reserved for cases in which a third person is also able to hear the sounds, either with the aid of a stethoscope, or as they emanate from the affected individual's ear. An example ofobjective tinnitus is "pulsatile tinnitus. Using the hypothetical locus of origin as a guiding principle, tinnitus has been divided into " otic or " peripheral tinnitus (associated with disorders of the inner ear and/or the acoustic nerve), " central tinnitus (associated with conditions affecting the CNS), and "somatic tinnitus (associated with peripheral conditions outside the ear). A different subdivision, also based on the condition's hypothetical locus of origin, yields a division of tinnitus into " conductive tinnitus, " sensorineural tinnitus, and " central tinnitus. Eti-ologically, tinnitus is associated with a broad range of conditions, including otitis media and externa, corpora aliena, impacted earwax, damage to the hair cells due to loud noises, conductive hearing loss, Ménière's disease, acoustic neuromata, multiple sclerosis, head injury, thyroid disease, hyperlipidaemia, vitamin B12 deficiency, mercury or lead poisoning, and the prior use of ototoxic therapeutics. Over 300 types of medication list tinnitus as a possible side effect. The most obvious of these are chloroquine, quinine, the salicylates, the group of non-steroid anti-inflammatory drugs (NSAIDs), and certain members of such groups as " antibiotics, chemotherapy drugs, and loop diuretics. The pathophys-iology of tinnitus is largely unknown, as is its site of neural mediation. Contemporary conceptual models tend to emphasize that tinnitus may be mediated by any part of the auditory pathways, i.e. anywhere between the peripheral ear and the auditory cortex. As sustained tinnitus arises most frequently as a consequence of hearing loss, it has traditionally been assumed that hearing loss and tinnitus have a common etiology. While most cases of hearing loss are attributed to peripheral pathology, tinnitus has traditionally been attributed mainly to peripheral pathology. Today the role of central mechanisms is considered at least equally important, in the sense that abnormal auditory signals are deemed capable of influencing neural plasticity within central auditory structures. As a consequence, tinnitus tends to be conceptualized as a condition which is mediated and sustained by central neural networks, although it would often seem to be triggered by peripheral damage. To give expression to these conceptual considerations, the term " acquired centralized tinnitus has been proposed.

   References

   Henry, J.A., Dennis, K.C., Schechter, M.A. (2005). General review of tinnitus. Prevalence, mechanisms, effects, and management. Journal of Speech, Language, and Hearing Research,, 48, 1204-1235.

   Morgenstern, L. (2005). The bells are ringing. Tinnitus in their own words. Perspectives in Biology and Medicine, 48, 396-407.

   Pliny the Elder (1601). The history ofthe world. Translated by Holland, P. London: Adam Islip.

   Vernon, J.A., Sanders, B.T. (2001). Tinnitus. Questions and answers. Boston, MA: Allyn and Bacon.