Chronic unilateral tinnitus, tinnitus research initiative new zealand - Review

Most cases of tinnitus are subjective, but occasionally the tinnitus can be heard by an examiner. Otologic problems, especially hearing loss, are the most common causes of subjective tinnitus. Objective tinnitus usually is caused by vascular abnormalities of the carotid artery or jugular venous systems. Initial evaluation of tinnitus should include a thorough history, head and neck examination, and audiometric testing to identify an underlying etiology. Unilateral or pulsatile tinnitus may be caused by more serious pathology and typically merits specialized audiometric testing and radiologic studies.
In patients who are discomforted by tinnitus and have no remediable cause, auditory masking may provide some relief. Epidemiologic data reveal that approximately one fourth of persons with tinnitus are discomforted by it, whereas the remaining three fourths experience the condition without significant symptoms.3Tinnitus takes different forms and has different classification proposals. One classification system stresses distinctions between vibratory and nonvibratory types, while another system groups the different forms of tinnitus into subjective or objective classes.Vibratory tinnitus is caused by transmission to the cochlea of vibrations from adjacent tissues or organs. Nonvibratory tinnitus is produced by biochemical changes in the nerve mechanism of hearing.Subjective tinnitus, which is more common, is heard only by the patient.

Objective tinnitus can be heard through a stethoscope placed over head and neck structures near the patient's ear.The mechanism that produces tinnitus remains poorly understood.
Tinnitus may originate at any location along the auditory pathway from the cochlear nucleus to the auditory cortex. Some leading theories include injured cochlear hair cells that discharge repetitively and stimulate auditory nerve fibers in a continuous cycle, spontaneous activity in individual auditory nerve fibers, hyperactivity of the auditory nuclei in the brain stem, or a reduction in the usual suppressive activity of the central auditory cortex on peripheral auditory nerve activity.4This article discusses the causes of subjective and objective tinnitus, and techniques used for evaluating tinnitus.
It is continuous and less disturbing than the tinnitus of Meniere's disease.14Ototoxic medications or substances are another common cause of bilateral tinnitus.
Temporomandibular joint disorder has been associated with vertigo and tinnitus, although the exact mechanism is unclear.Various metabolic abnormalities may be associated with tinnitus.
These abnormalities include hypothyroidism, hyperthyroidism, hyperlipidemia, anemia, and vitamin B12 or zinc deficiency.Many patients with tinnitus exhibit signs of psychologic disorders. Although tinnitus may be a contributing factor to the development of depression, the common association of tinnitus and depression may be the result when depressed patients, particularly those with sleep disturbances, focus and dwell on their tinnitus more than patients who are without an underlying psychologic disorder.OBJECTIVE TINNITUSObjective tinnitus is rare. Patients with objective tinnitus typically have a vascular abnormality, neurologic disease, or eustachian tube dysfunction.4Patients with vascular abnormalities complain of pulsatile tinnitus.
This type of tinnitus is a soft, low-pitched venous hum, which can be altered by head position, activity, or pressure over the jugular vein.4Congenital arteriovenous shunts are usually asymptomatic, while the acquired type often are associated with pulsatile tinnitus.


The symptoms may disappear with Valsalva's maneuver or when the patient lies down with the head in a dependent position.Evaluation of TinnitusHISTORYThe evaluation of a patient with tinnitus begins by taking a thorough history. Precipitous onset can be linked to excessive or loud noise exposure or head trauma.LocationUnilateral tinnitus can be caused by cerumen impaction, otitis externa, and otitis media. Tinnitus associated with unilateral sensorineural hearing loss is the hallmark of acoustic neuroma.PatternContinuous tinnitus accompanies hearing loss. Tinnitus of venous origin can be suppressed by compression of the ipsilateral jugular vein.Specific testing for sensorineural or conductive hearing loss is the next part of the examination. Patients with unilateral or pulsatile tinnitus are more likely to have serious underlying disease and typically merit referral to an otolaryngologist.2,5 A full clinical evaluation should precede radiologic studies.
Because pulsatile tinnitus suggests a vascular abnormality, the preferred imaging study is contrast-enhanced computed tomography (CT) or magnetic resonance imaging (MRI) of the brain21 (Figure 2).

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