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ARTICLE  
Year : 2014  |  Volume : 16  |  Issue : 69  |  Page : 69-72
Relation of distortion product otoacoustic emission and tinnitus in normal hearing patients: A pilot study

1 Department of Otolaryngology, C.U. Shah Medical College, Surendranagar, Gujarat, India
2 C.U. Shah School of Audiology and Speech Therapy, Surendranagar, Gujarat, India

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Date of Web Publication7-May-2014
 
  Abstract 

Introduction: Tinnitus, the perception of the sound in the absence of an external acoustic source, disrupts the daily life 1 out of every 200 adults, yet its physiological basis remains largely a mystery. The generation of tinnitus is commonly linked with the impaired functioning of the outer hair cells (OHC) inside the cochlea. Otoacoustic emissions are the objective test used to assess their activity. Objective: The objective of the investigation was to study the features of Distortion product OtoAcoustic emissions (DPOAE) in a group of tinnitus patients with normal hearing and to find out whether there is any difference in DPOAE findings in the tinnitus patients with normal hearing and in persons with normal hearing with no complaint of tinnitus. Materials and Methods: The participants consisted of two groups. The subject group consisted of 16 ears of patients, in which 6 subjects were having tinnitus in both ears while 4 subjects were having tinnitus only in one ear. All subjects were aged between 20 to 60 years with complaint of tinnitus with audiometrically normal hearing. Control group was comprised of 16 audiometrically normal hearing ears of persons who were age and gender matched with the subject groups and had no complaint of tinnitus. Both the subject group as well as control group was subjected for DPOAE test. Findings of both the groups were compared using the unpaired t test. Result and conclusion: It was observed that the amplitudes of DPOAE were significantly lower in tinnitus patients than that of persons without complaint of tinnitus, at a frequency of 1281-1560, 5120-6250, 7243-8837 Hz, which imply that decrease of DPOAEs amplitudes may be related to the presence of tinnitus. It can be concluded that there is association between tinnitus and reduced OHC activity which indicate the OHC of cochlea are involved in the generation of tinnitus.

Keywords: Cochlear activity, distortion product otoacoustic emission, tinnitus with normal hearing

How to cite this article:
Modh D, Katarkar A, Alam N, Jain A, Shah P. Relation of distortion product otoacoustic emission and tinnitus in normal hearing patients: A pilot study. Noise Health 2014;16:69-72

How to cite this URL:
Modh D, Katarkar A, Alam N, Jain A, Shah P. Relation of distortion product otoacoustic emission and tinnitus in normal hearing patients: A pilot study. Noise Health [serial online] 2014 [cited 2019 Jun 26];16:69-72. Available from: http://www.noiseandhealth.org/text.asp?2014/16/69/69/132078

  Introduction Top


Tinnitus, the perception of the sound in the absence of an external acoustic source, disrupts the daily life of 1 out of every 200 adults, yet its physiological basis remains largely a mystery. [1] This symptom is highly associated with hearing loss. [2] The association between tinnitus and hearing loss has already been proven. According to different reports, 85-96% of patients with tinnitus present with some levels of hearing loss and only 8-10% have normal hearing. In this last group, the isolated presence of tinnitus indicates that it may be an initial first symptom of diseases that are only diagnosed after the onset of hearing loss. The origin of tinnitus in this group is still more obscure than in those with concomitant hearing loss. [3]

Recent advances in the study of the cochlear mechanical process suggest that one source of tinnitus may be related to cochlear mechanical activity; damage to outer hair cells (OHCs) of the cochlea is believed to be one of principal mechanism of tinnitus. If the OHC of the human cochlea are to be involved in the generation of tinnitus, testing of otoacoustic emissions (OAEs) could provide a reliable means of recording OHC dysfunction. [4]

Distortion product otoacoustic emission (DPOAE) is a type of OAE in which the stimulus consist of two different pure tones of two different frequencies (i.e., F1 and F2; F2 >F1) and two intensity levels (i.e., L1 and L2; L1 >L2) the relationship between L1/L2 and F1/F2 dictates the frequency response. DPOAEs can be recorded with better reliability at higher frequencies than transient evoked OAE. Therefore, it is useful for detection of cochlear damage. [5] Patients with tinnitus and normal hearing constitute an uncommon group and there is rare literature on tinnitus cases with normal hearing.


  Objective Top


The primary objective of this study was to find out the relation of DPOAE with the tinnitus in normal hearing patients at all audiometric testing frequencies ranged from 500 to 8000 Hz, in order to test the hypothesis that cochlear OHCs function may be involved in the generation of tinnitus.


  Methods Top


This was a retrospective study carried out at C.U. Shah Medical College, Surendranagar, Gujarat. At the beginning of the study, random selection of patients with tinnitus of different age groups and both gender was done during the period of 6 months (January 2012 to June 2012).

Study group

Consisted of 10 patients, aged ranges between 20 and 65 years complaining of tinnitus with audiometrically normal hearing, among them six were having bilateral and four were having unilateral tinnitus (n: 12 + 4 = 16).

Control group

Consisted of 16 normal hearing individuals without tinnitus with pure tone average <25 dBHL in the better ear. Either ear of individuals without hearing loss was taken in the control group (n: 16).

Exclusion criteria

History of ototoxic or otropic drug intake, history of exposure to noise, history of ear surgery:

  1. Otoscopic examination: Otoscopic investigation of the external and middle ear were carried out on each patient to evaluate any disorders.
  2. Pure tone audiometry: Hearing threshold levels measurements carried out in the range of 250-8000 Hz using descending 10 dB step size and 5 dB step size to determine the lowest threshold. All measurements were carried out by a qualified audiologist in an isolated test booth using clinical diagnostic audiometer (orbiter 922 Madsen).
  3. Tympanometry: Test of the middle ear function was carried out using middle ear analyzer (GSI-TYMPSTAR).
  4. DPOAE: It was obtained in the frequency range of 500-8000 Hz using smart DPOAE-intelligent hearing systems. Recording was done from 16 ears of the selected patients with tinnitus (the study group) and 16 ears of audiometrically normal hearing individuals without tinnitus (the control group). Custom software was used to generate the primaries and to record the ear canal signals. The stimuli used for DPOAE measurement were continuously sweeping primaries with a fixed primary ratio (f2/f1) of 1.22. [6] Recording were repeated twice to ensure the reliability of the results.



  Results Top


[Table 1] shows the mean DPOAE amplitude of both groups, the study group with tinnitus (n = 16) and the control group without tinnitus (n = 16). [Figure 1] and [Figure 2] show diagrammatic presentation of DPOAE distribution where as [Figure 3] shows the error bar of the data assessed derived from standard error of both groups. There are some differences in the mean DPOAE amplitude levels between the study and the control groups. The study group showed decreased amplitude in the tested frequencies. Among them at few frequencies differences between the mean DPOAEs amplitudes of both groups were significant at P < 0.05, noticed at following tested frequencies: 1281-1560 Hz, 5120-6250 Hz and 7243-8837 Hz. These differences were being in the size of 4.47 dB average.
Figures 1 and 2: Diagrammatic presentation of distortions product otoacoustic emission (DPOAE) distribution (Series 1: DPOAE of control group mean, Series 2: DPOAE of study group mean)

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Figures 1 and 2: Diagrammatic presentation of distortions product otoacoustic emission (DPOAE) distribution (Series 1: DPOAE of control group mean, Series 2: DPOAE of study group mean)

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Figure 3: Error bar of the data assessed derived from standard error of both groups

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Table 1: Mean of DPOAE amplitudes (dB) of the study and control group with its t value and P value

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  Observation Top


Unpaired Student's t-test was used to calculate the significant differences at P < 0.05 between the mean DPOAEs amplitude of the study and the control groups.


  Discussion Top


The results of the present study revealed significant decreases in the DPOAEs amplitude over the tested frequencies range in most of the tinnitus patients with normal hearing compared with non-tinnitus patients with normal hearing. The amplitudes of DPOAE were significantly lower in tinnitus patients than that of normal patients at a frequency of 1281-1560, 5120-6250, 7243-8837 Hz, which imply that decrease of DPOAEs amplitudes may be related to the presence of tinnitus.

Our results are consistent with the results obtained by Shiomi et al., [4] Igna et al., [7] Favero et al., [8] Vicky et al.[9] and Granjeiro et al. [10] that there was a significant decrease in DPOAEs amplitudes over a limited frequency range observed in the normal hearing tinnitus group when compared to the non-tinnitus normal hearing group.

Impaired cochlear function correlates with the presence of tinnitus and its estimated spectral profile. [11] Decrease in the DPOAEs amplitude indicates dysfunction of the OHC. This dysfunction may be due to discordant inner hair cells (IHC) and OHC damage, i.e., damaged OHC with reasonably intact (IHC). [12] The OHC are more prone to damage and when it occurs, they fail to perform the inhibition over the IHC function. This loss of IHC inhibition results then in tinnitus. Tinnitus in turn, which is an unpleasant sound, may act as a noise which resulted in a decrease of the DPOAEs amplitudes due to increase in the internal ear noises heard by the patients as ringing noises. This noise is one of the factors that result either in the absence or decrease in DPOAEs amplitudes. In the presence of these results, tinnitus masker could be a good solution for the relief of annoyance resulted from tinnitus. Here, we would like to focus one more fact that a decrease of the DPOAE amplitude is not only a result of a cochlear insult. It might be as well an efferent effect. Efferent innervation of OHC is by the olivo cochlear neural pathway which is comprised of efferent neurons that travel from the superior olivary complex in the brainstem to cochlear hair cells. Measurements of efferent effects on OAEs have been made with efferent activity evoked by brainstem shocks or by sound in the opposite ear. Various investigations have supported the conclusion that medial olivo cochlear system activity turns down the gain of the cochlear amplifier. [13] Here cochlear amplifier term is associated with OHCs. DPOAE suppression is greatest when using contralateral stimulation tones close to primary tone f2. [14]

Our study has certain limitations. The sample size is small which may have decreased the statistical power. However, in our present study, we successfully determined a statistically significant difference in three frequencies out of eight total tested frequencies. More information can be obtained using a larger sample size which will add to the knowledge about the possible link of OHC functioning and tinnitus.


  Conclusion Top


From this presented study, in the context of tinnitus generating mechanism, it is observed that the DPOAE amplitude are significantly reduced in patients of tinnitus with normal hearing at certain frequencies compared to normal individuals. Thus, it can be hypothesized that there is an association between tinnitus and reduced cochlear OHC activity which indicate that the OHC of the cochlea are involved in the generation of tinnitus. Hence this signifies the importance of DPOAEs in patients of tinnitus with normal hearing. However, studies with larger patient series would be required in order to strengthen the hypothesis.

 
  References Top

1.Coles RR. Epidemiology of tinnitus: (1) prevalence. J Laryngol Otol Suppl 1984;9:7-15.  Back to cited text no. 1
[PUBMED]    
2.Lockwood AH, Salvi RJ, Burkard RF. Tinnitus. N Engl J Med 2002;347:904-10.  Back to cited text no. 2
    
3.Sanchez TG, Medeiros IR, Levy CP, Ramalho Jda R, Bento RF. Tinnitus in normally hearing patients: Clinical aspects and repercussions. Braz J Otorhinolaryngol 2005;71:427-31.  Back to cited text no. 3
    
4.Shiomi Y, Tsuji J, Naito Y, Fujiki N, Yamamoto N. Characteristics of DPOAE audiogram in tinnitus patients. Hear Res 1997;108:83-8.  Back to cited text no. 4
    
5.Komazec Z, Miloseviæ D, Filipoviæ D, Dankuc D. Otoacoustic emissions - A step closer to understanding cochlear function. Med Pregl 2001;54:539-42.  Back to cited text no. 5
    
6.Long GR, Talmadge CL, Lee J. Measuring distortion product otoacoustic emissions using continuously sweeping primaries. J Acoust Soc Am 2008;124:1613-26.  Back to cited text no. 6
    
7.Igna CD, Schmidt LP, Smith M, Facchini L, Kang S. Otoacoustic emission in patients with tinnitus and normal hearing. Otolaryngol Head Neck Surg 2004;131:279.  Back to cited text no. 7
    
8.Favero M, Bento RF, Sanches TG, Nascimento AF. Contra lateral suppression of otoacoustic emission in subject with tinnitus. Otolaryngol Head and Neck Surg 2004;131:260.  Back to cited text no. 8
    
9.Vicky W, McPherson B. Otoacoustic emissions research in China: Breaking the language barrier; Guest editorial in oae.it (otoacoustic emissions portal zone, September-november 2005.  Back to cited text no. 9
    
10.Granjeiro RC, Sampaio AL, Kehrle M, Oliveria C, Furtado V. P099 otoacoustic emissions in patients with tinnitus. Otolaryngol Head Neck Surg 2006;135 Suppl 1:245-6.  Back to cited text no. 10
    
11.Zhou X, Henin S, Long GR, Parra LC. Impaired cochlear function correlates with the presence of tinnitus and its estimated spectral profile. Hear Res 2011;277:107-16.  Back to cited text no. 11
    
12.Jastreboff PJ. Phantom auditory perception (tinnitus): Mechanisms of generation and perception. Neurosci Res 1990;8:221-54.  Back to cited text no. 12
[PUBMED]    
13.Siegel JH, Kim DO. Efferent neural control of cochlear mechanics? Olivocochlear bundle stimulation affects cochlear biomechanical nonlinearity. Hear Res 1982;6:171-82.  Back to cited text no. 13
[PUBMED]    
14.Wolter NE, Harrison RV, James AL. Investigation of olivocochlear and middle ear muscle reflexes with contralateral suppression of DPOAEs in real time; [abstract]. Triological Society Eastern Section Annual Resident Competition - Podium Presentation, 2011.  Back to cited text no. 14
    

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Correspondence Address:
Asst. Prof. Noorain Alam
C.U. Shah School of Audiology and Speech Therapy C-22, C.U. Shah Medical College Campus, Dudhrej Road, Surendranagar, Gujarat
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1463-1741.132078

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