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