1

Introduction

Noise-induced tinnitus is continuous, nonpulsating, and persistent in nature. Its source may lie anywhere along the auditory system (center, periphery, or both). Tonndorf suggested that tinnitus is a manifestation of the spontaneous depolarization of the auditory fibers, which creates noise without an external auditory stimulus. According to Kemp , activation of the central auditory system is a prerequisite for the appearance of tinnitus. In the absence of an external source, the author speculated that the activation was induced by an abnormality or desynchronization of the auditory or related system(s), which was interpreted by the perceptual system as tinnitus. It is also possible that tinnitus is caused by electrochemical abnormalities in the cochlear hair cells, which lead to an abnormal discharge of action potentials to the adjacent nerve fiber.

Hearing loss is not a mandatory criterion for tinnitus . The standard audiogram in some patients with noise-induced tinnitus might be explained by the study of Shulman , which reported damage only at frequencies higher than 8 kHz, or by subclinical impairments overlooked by the standard audiometric measures. Parving et al noted persistent tinnitus after labyrinthectomy or eighth-nerve section; and Coles showed that some tinnitus properties, such as onset, offset, and sensation level, could change considerably without affecting the audiogram. Attias et al , in a study of patients with noise-induced hearing loss (NIHL) with and without tinnitus, found identical brain stem activity in both groups. However, event-related brain potentials were significantly lower in amplitude in the patients with tinnitus compared with age- and hearing-matched control subjects. They concluded that the changes in tinnitus are secondary to central nervous system changes, and cognition and sound perception are involved at a higher level. These findings confirmed the earlier animal study by Gerken et al wherein chronic stimulation of the peripheral auditory system caused an adaptive hyperactivity in central areas.

In patients with NIHL, rates of tinnitus range from 35% to 77% . Using extended high-frequency audiometry, Barnea et al found that 6% of patients exposed to damaging noise have tinnitus with a normal audiogram. No significant difference in audiometric measures was recorded between patients with normal audiograms, with and without tinnitus.

Regarding sidedness, tinnitus has been reported to be more frequent in the left ear than the right . Similar findings from a recent study pointed to more vulnerability of the left ear compared with the right . Chermak and Dengerinck reported bilateral tinnitus in 52% of patients. However, Cahani et al noted that, when hearing loss was more severe in the right ear, there was right-sided tinnitus and, when hearing loss was more pronounced in the left ear, the tinnitus was bilateral or more pronounced on the right. The sensation level of tinnitus was only 5 to 10 dB at the tinnitus-matched frequency .

The quantification of tinnitus is important for several reasons: to reassure the patient that the symptom is real, to provide information that might help clinicians identify the site of origin of tinnitus in the auditory system, to monitor changes in tinnitus, and to assist in legal issues.

To assist in patient evaluation, researchers have defined and analyzed several specific properties of tinnitus. Pitch perception is thought to be coded by both place of stimulation and rate of temporal activity. Thus, a high-pitched sound may correspond to high-frequency vibration in the basal cochlear portion of the inner ear; and low-pitched sound, to low-frequency neural activity at the apical part of the basilar membrane. Thus, because most patients with tinnitus have high-tone loss, the pitch rates most frequently reported range from 3000 to 6500 Hz . By contrast, in middle ear dysfunction, the most prominent pitch range reported is 125 to 2000 Hz . However, the reliability of tinnitus pitch measurements may be influenced by several factors, including the testing strategy, the source of the tinnitus, and the homogeneity of the sample. For example, Tyler and Conrad-Armes noted that, in some patients, the pitch match covered a range of 1 octave. Burns found that pitch matching to tinnitus could be 10 or 20 times larger than matching to pure tones. Penner and Saran attempted various adaptive procedures to limit variability.

Loudness may serve as a good parameter for tinnitus management . Therefore, clinicians also need to focus more attention on patient perception and tolerance of tinnitus and their adaptation to it. The variability of loudness adjustments is typically low, especially at the tinnitus pitch, although it does differ across patients .

The aim of the present study was to examine the test-retest value of tinnitus pitch and loudness in patients with NIHL.

2

Methods

The study sample consisted of 30 patients of mean age 35 ± 6.7 years (average, 45.6 years) with long-standing tinnitus and hearing loss due to exposure to impulsive or continuous noise during military service. The subjects were referred to an annual examination to follow NIHL. Ten patients had unilateral tinnitus (7 in left ear and 3 in the right ear); 20, bilateral tinnitus. All presented with a typical NIHL audiogram on the affected side(s). Each patient with unilateral tinnitus and hearing asymmetry underwent a detailed medical examination (including magnetic resonance imaging scan) to exclude a retrocochlear lesion. None of the patients was receiving drug therapy. The patients were included only after signing a written informed consent and receiving a detailed explanation regarding the process.

At the first study visit, an audiogram was performed in all patients to determine bone and air thresholds at the frequency range of 0.25 to 8 kHz. These tests were then repeated at a second visit, 1 to 2 years later.

All tests were performed by a qualified audiologist in a standard soundproof room using a GSI-16 audiometer and calibrated earphones (type TDH39) (Grason-Stadler, Madison, WI, USA).

2

Methods

The study sample consisted of 30 patients of mean age 35 ± 6.7 years (average, 45.6 years) with long-standing tinnitus and hearing loss due to exposure to impulsive or continuous noise during military service. The subjects were referred to an annual examination to follow NIHL. Ten patients had unilateral tinnitus (7 in left ear and 3 in the right ear); 20, bilateral tinnitus. All presented with a typical NIHL audiogram on the affected side(s). Each patient with unilateral tinnitus and hearing asymmetry underwent a detailed medical examination (including magnetic resonance imaging scan) to exclude a retrocochlear lesion. None of the patients was receiving drug therapy. The patients were included only after signing a written informed consent and receiving a detailed explanation regarding the process.

At the first study visit, an audiogram was performed in all patients to determine bone and air thresholds at the frequency range of 0.25 to 8 kHz. These tests were then repeated at a second visit, 1 to 2 years later.

All tests were performed by a qualified audiologist in a standard soundproof room using a GSI-16 audiometer and calibrated earphones (type TDH39) (Grason-Stadler, Madison, WI, USA).