Elsevier

Auris Nasus Larynx

Volume 37, Issue 1, February 2010, Pages 55-60
Auris Nasus Larynx

DPOAE in estimation of the function of the cochlea in tinnitus patients with normal hearing

https://doi.org/10.1016/j.anl.2009.05.001Get rights and content

Abstract

Objective

The most probable place generating tinnitus in the auditory pathway is the outer hair cells (OHCs) inside the cochlea. Otoacoustic emissions are used to assess their activity. The objective of the investigation was to measure the features of distortion product otoacoustic emissions (DPOAE) in a group of tinnitus patients without hearing loss, estimate the diagnostic value of the parameters for the analysis of cochlear function in the patients, emphasizing those most useful in localizing tinnitus generators, and determine the hypothetical influence of hyperacusis and misophony on DPOAE parameters in tinnitus patients.

Patients and methods

The material consisted of 44 patients with tinnitus and without hearing loss. In the control group were 33 patients without tinnitus with the same state of hearing. The tinnitus patients were divided into three subgroups: those with hyperacusis, those with misophonia, and those with neither. After collecting medical history and performing clinical examination of all the patients, tonal and impedance audiometry, ABR, and discomfort level were evaluated. Then DPOAE were measured using three procedures. First the amplitudes of two points per octave were assessed, second the “fine structure” method with 16–20 points per octave (f2/f1 = 1.22, L1 = L2 = 70 dB), and the third procedure included recording the growth function in three series for input tones of f2 = 2002, 4004, and 6006 Hz (f2/f1 = 1.22) and L1 = L2 levels increasing by increments of 5 dB in each series.

Results and conclusions

Hyperacusis was found in 63% and misophonia in 10% of the tinnitus patients with no hearing loss. DPOAE amplitudes in recordings with two points per octave and the fine structure method are very valuable parameters for estimating cochlear function in tinnitus patients with normal hearing. Function growth rate cannot be the only parameter in measuring DPOAE in tinnitus patients, including subjects with hyperacusis and misophonia. The markedly higher DPOAE amplitudes in the group of tinnitus patients without hearing loss suggest that tinnitus may be caused by increased motility of the OHCs induced by decreasing efferent fiber activity, and not by OHC failure. Hyperacusis significantly increases the amplitude of DPOAE in tinnitus patients with no hearing loss.

Introduction

Tinnitus is a serious problem, with increasing numbers of patients, including children, suffering from this disease. About 35% of adults have had some experience with tinnitus [1]. Tinnitus is defined as a sense of sound without external stimuli [2], [3], [4]. The opinions about the cause and location of tinnitus generation are not unanimous, but the cochlea and outer hair cells (OHCs) probably play a crucial role in its pathogenesis. It would be interesting to determine whether otoacoustic emissions are a useful tool in the evaluation of OHCs as a tinnitus generator. According to Shiomi et al. [5], measuring distortion product otoacoustic emissions (DPOAE) is the basic method that allows one to evaluate properly the mechanical activity of the cochlea in tinnitus patients. Hyperacusis plays an important role in these patients and it may often be a forerunner of tinnitus [6]. It is defined as an unpleasant, often painful, feeling caused by sound due to hyperactivity of the compensatory action of the central nervous system. Epidemiological data indicate that about 40% of tinnitus patients worldwide suffer from hyperacusis [2], [7]. Misophonia and phonophobia are different from hyperacusis and result from pathological excitement of the limbic system, which is responsible for emotions [8], [9].

Section snippets

Aims of the study

  • 1.

    To measure the features of DPOAE in tinnitus patients group without hearing loss;

  • 2.

    To determine the diagnostic value of DPOAE parameters for an analysis of cochlear function in the patients, emphasizing the DPOAE parameters most useful in localizing tinnitus generators;

  • 3.

    To determine the influence of hyperacusis and misophonia on DPOAE parameters in tinnitus patients.

Material

The inclusion criterion was neuro-otological tinnitus, but not tinnitus generated by way of sound conduction to the cochlea (called otologic tinnitus according to Shulman [10]). In this way, only patients with tinnitus generated along the auditory pathway were considered. The study group (NT) consisted of 44 patients (22 females and 22 males, 75 ears tested) with tinnitus and audiologically proper hearing examined in the ENT Department of Wrocław University in 2001–2004. The average age of the

Method

A detailed history was taken in each case, with particular attention to ENT diseases, especially tinnitus. In each case a physical ENT examination was performed to exclude any pathology that might influence the condition of the hearing organ. Then a battery of audiological tests was performed in each case: pure tone audiometry with discomfort level evaluation, impedance audiometry, and brainstem auditory evoked potentials. Based on these tests, only patients with proper hearing were qualified

Results

First DPOAE of the right and left ears in the NT and N groups were compared. No statistically significant differences were observed between the sides. Further statistical analysis was therefore performed for both sides together. In the next step the number of the cases in which DPOAE were present in the registration of two points per octave as well as the fine structure in the N and NT groups was evaluated. Except for two cases, no statistically significant differences in DPOAE were present

Discussion

Tinnitus is complex in its genesis, perception, and interpretation of the patient. It is generated not only in the inner ear, but also in some parts of the limbic system (mostly the amygdaloid nucleus), thalamus nuclei, hippocampus, and hypothalamic paraventricular nucleus take part in the process [7], [11], [15], [16], [17], [18], [19], [20]. Activation of the auditory cortex and other parts of the central nervous system is also crucial in tinnitus detection, although, according to Bartnik [2]

Conclusions

  • 1.

    DPOAE amplitude recorded at two points per octave and in the fine structure is a valuable parameter in cochlear evaluation in tinnitus patients;

  • 2.

    The fine structure provides extra information about DPOAE amplitude expanding f2 frequency range for which differences between the groups exist;

  • 3.

    The growth rate function cannot be the only parameter used to evaluate DPOAE in tinnitus patients or patients with misophonia and hyperacusis. It cannot replace DPOAE amplitude analysis in tinnitus patients;

  • 4.

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