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Address for correspondence : Moon Suh Park, MD, PhD, Department of Otorhinolaryngology-Head and Neck Surgery, Kyung Hee University School of Medicine, 892 Dongnam-ro, Gangdong-gu, Seoul 134-727, Korea
Tel : +82-2-440-6237, Fax : +82-2-440-6296, E-mail : pmsuh@yahoo.co.kr
Introduction
Tinnitus is an abnormal sound, which is felt with no stimulation, and about 8-10% of people suffer from this condition. Most of the people amongst 8-10% have become as well as being habituated to tinnitus, and about 1% of them are seriously suffering from the inconvenience caused by the condition.1) Tinnitus is usually a subjective symptom, which could also be expressed by duration and frequency components. Clinically, patients can express tinnitus by using the method to speak similar voices like tinnitus or indicate similar sounds around themselves. However, such a strategy might cause differences between the individuals and it is not easy to evaluate psychoacoustic characteristics because of
ones' own diverse auditory experiences. Therefore, the recent methods to evaluate tinnitus have definite limitations, although a number of methods have been developed, which express tinnitus in a more objective way as per the feelings of the patients.
Meanwhile, the presence of tinnitus has been recently considered as a criterion for determining the degree of the disability caused by various industrial, but there is no way to objectively prove the presence of tinnitus. However, we can objectively employ the auditory brainstem response test to evaluate the degree of hearing loss.
Therefore, in the present study, our aim was to find the usefulness of the repeated tinnitogram in diagnosing the presence of tinnitus.
Materials and Methods
The study was conducted in 50 patients, who have been suffering from continuous tinnitus for more than 6 months since 2006, and in 20 virtual tinnitus patients (non-tinnitus group) who were assumed to be complaining of tinnitus (actually they do not have any symptoms of tinnitus). Moreover, we excluded the patients who had problems in communicating due to severe hearing loss on both ears, while there were no restrictions with respect to gender, age, cause of tinnitus, duration, direction of progress, and degree of disability. In case of virtual tinnitus patients, volunteers with normal hearing and no experience of tinnitus were also selected for the present study. The average age for the tinnitus patient group was 55 years (14-80 years) and 27 years (23-33 years) for the non-tinnitus patient group (Table 1).
Otologic (hearing) evaluation
For hearing evaluation, an audiometer (GN otometrics, Orbiter model 922, Chicago, IL, USA) was used to measure individual thresholds for pure tones of 125, 250, 500, 1,000, 2,000, 3,000, 4,000, 6,000, and 8,000 Hz frequencies for more than twice. If any threshold for the respective frequencies was found to be above 26 dB, the condition was diagnosed as hearing loss. For non-tinnitus group, there was no hearing loss on both ears.
Measurement of tinnitus
Fixed frequency-pitch match test
Pure tone and narrow band noise were used according to the range of loudness and frequency. As pure tone, sounds generated in the audiometer (GN otometrics, Orbiter model 922, Chicago, IL, USA) were used, and, as for frequencies, 11 kinds of frequencies were used: 125, 250, 500, 750, 1,000, 1,500, 2,000, 3,000, 4,000, 6,000, and 8,000 Hz. Loudness of tinnitus had the range from 0 to 110 dB, which were adjustable at intervals of 1 dB. The most similar frequency was found by asking the patients about the frequency, which was most similar to their tinnitus, and then moving the dissimilar side to the similar side scale by scale. In the beginning, when it was not possible to find the similar tone through the pure tone test, the test was conducted with narrowband noise. When no similar tone was found even through narrowband noise, white noise and voice signal noise were used in order to figure out the kinds of sounds. However, white noise and voice signal noise are not specific with respect to the frequency, and thus those who selected white noises or voice signals amongst the tinnitus and non-tinnitus groups, were excluded from the statistical analysis of the frequency.
Loudness balance test
With the pitch match test, the frequencies of tinnitus were found, and the loudness of tinnitus was measured by repetitions to ascend and descend the frequencies by 5 dB from hearing threshold values at a time for 2-3 seconds.
Measurement of Loudness Matching by Tinnitogram Tinnitogram was conducted in 50 tinnitus patients and 20 non-tinnitus patients, and non tinnitus patients were made to participate in the test by freely setting their own virtual tinnitus, and then the stimulating sounds were transmitted through TDH 49 (headphone) in all the tests, and conducted in a quiet sound-proof room. For the measurement of loudness matching by tinnitogram, the fixed frequency-pitch match test and the loudness balance test were used, and conducted thrice in the same way at intervals of 1 minute for the analysis of the consistency of the test results between the groups.
Statistical analysis
Statistical significance evaluation between the two groups was conducted in order to find the difference of their average hearing results between the test intervals, and
Student's t-test was used to compare the difference between both the groups. p-value below 0.05 was considered as significant.
Results
In the tinnitus group, tinnitus accounted in 36 patients (72%) in pure tone, 12 patients (24%) in narrowband noise, and 1 patient (2%) each in white noise and voice signal noise. The result of this group was more diverse than that of the non-tinnitus group comprising of 18 patients (90%) in pure tone, 0 patient, 2 patients (10%) in white noise, and 0 patient. In both the groups, tinnitus in the pure tone was found with the highest frequency (Fig. 1).
Based on the analysis of patients with tinnitus of pure tone and narrow band noise, the tinnitus group showed the high frequency of tinnitus in the high frequency domains with 14 patients (29%) in 4,000 and 12 patients (25%) in 8,000 Hz, respectively (Fig. 2).
Tinnitus frequencies performed three times showed no difference among each result in both the tinnitus and non-tinnitus group. Verage frequency of tinnitus group was 3,300 Hz and non-tinnitus group 1,283 Hz in non tinnitus group.
With respect to the measurement of the loudness of tinnitus, the tinnitus group showed 7.28 dBSL (±6.29) on an average, and the non-tinnitus group showed 13.6 dBSL (±8.14) on an average. In other words, the loudness of the non-tinnitus group was found to be higher than that of the tinnitus group, and this result was considered to be statistically significant
(p<0.05)(Fig. 3).
On the basis of comparison of the loudness differences, which were repeatedly measured, the result of tinnitus group showed 7.16 (±4.23), 7.36 (±5.24), and 7.32 (±3.32) dBs. And it had no significant difference among each consecutive result of loudness
(p-value of 0.56). However, in the non-tinnitus group, the results showed 11.67 (±6.10), 16.2 (±8.66), 12.8 (±9.12) dBs, respectively on an average with three consecutive measurements, it had significant difference among each consecutive result of loudness
(p=0.016)(Table 2).
Discussion
The pathological physiology of tinnitus has yet not clearly been revealed, but there exists many multi-functional possibilities. Tinnitus is an aberrant neural signal, which is recognized by sound, but the origin of such a signal is still controversial. Till date there are 2 theories on the origin of tinnitus; firstly, tinnitus could occur from auditory nerves or from a much lower level, and also from the peripheral auditory nerve system, but the neural activity, which is directly related with tinnitus occurs from the upper level of auditory nerves.2,3) Secondly, a majority of tinnitus conditions are subjective rather than objective,4,5,6) and it is difficult to objectively express the condition because the subjective tinnitus is expressed by
patient's own complaints. Locating the position of tinnitus also has certain grey areas, and thus there are various cases of patients indicating ears, head, or the air as the source of tinnitus.
As objective methods to measure tinnitus, the fixed frequency-itch match test and the loudness balance test are most commonly employed, but they have their own limitations. Pitch match test has the limitation to distinguish differences because more than 2/3rd of tinnitus patients complain of their tinnitus other than pure tones, so it is difficult to evaluate tinnitus, and there is a problem in avoiding the octave confusion phenomenon as well. In addition, the loudness balance test has some confusion with respect to diagnosis because there are many instances of patients complaining about louder tinnitus than the real sound, which can be represented as
'loudness recruitment phenomenon'. Actually, the reliability of tinnitogram result has been an issue at all the times. According to a previous study, the consistency between frequencies of the pitch match test and the masking test reached to about 42%, and the loudness of tinnitus coincided at about 15% in the loudness balance test and the masking test, so there were some difference in terms of the consistency exhibited by both the tests.7)
In terms of considering the main objective of tinnitus expression, accurate diagnosis of the presence of tinnitus is imperative. At present, in terms of otologic disability determination caused by industrial accidents, the presence of tinnitus could influence the determination of the disability degree, and actually, there have been many disputes on various insurance payment issues with the sharp increase in the frequency. However, until now, there were no other alternatives for the objective diagnosis of the presence of tinnitus, and no referential tests to support any inferences. Therefore, this study was initiated with expectations to have useful clues as references in terms of diagnosing the presence of tinnitus with the repeated tinnitograms.
Recently, Henry, et al.8,9) performed the pitch match test and the loudness balance test on 12 patients of the tinnitus group and the non-tinnitus group each, and found that the tinnitus group showed the louder tinnitus than the non-tinnitus group. However, in this study, the result was contradictory with the results from the non-tinnitus group (having the louder tinnitus), but if we consider that settings of tinnitus in the non-tinnitus group were freely made by the patients. Actually, the non-tinnitus patients group as volunteers was targeted for this study, and so they were of the younger age group than the tinnitus patients group. Furthermore, this suggests that more patients are required to conduct the study in order to find out the different characteristics between tinnitus and the non-tinnitus group, and select the patients group, which exhibit similar characteristics such as, age of tinnitus patients. In addition, when the pitch match tests were performed thrice, there was no difference between both the groups, but some significant differences were shown by the non-tinnitus group in 3 loudness tests, unlike the tinnitus group. Based on the study results, it might be considered that the repeated tinnitogram could be useful to diagnose the presence of tinnitus in malingering patients with no tinnitus symptoms, but there has been no standard set for
test's interval and frequency; and thus it is required to have more in-depth studies in the future for the repeated tinnitogram for diagnosing
tinnitus' malingering. Different from the precedent studies, in this study, the test at 1 minute intervals was adopted in order to repeat the loudness and the pitch tests with the possible shortest interval, because there is a possibility that tinnitus might keep changing even on a timely basis. However, 1 minute might be too short to exclude the effect of the memory, and it might be required many examination to vertify accurate test intervals. For evaluation methods of tinnitus, there are the residual inhibition test and minimal masking level tests on top of the pitch match test and the loudness balance test. The minimal masking level test uses the method to have the minimal masking level by masking tinnitus with broadband noises of tinnitus frequency which is acquired through the pitch match test, and the residual inhibition test takes the method to use the phenomenon in which the loudness of tinnitus is either lowered or tinnitus cannot be felt, hence this is an important index to evaluate
masking's usefulness and further determine its treatment. Typically, 80-90% of tinnitus patients have been reported to feel the masking on their own, and thus masking test method could be considered as useful in terms of the diagnosis and the treatment of tinnitus.10,11) Therefore, if the study to distinguish the presence of tinnitus, which has been confined to the loudness and the pitch until now, could be extended to the residual inhibition and the minimal masking level tests, it might be possible to have more meaningful and significant results. In addition, the number of population in this study was much more than in the precedent studies, which might be one of the reasons for reliability, but subsequent studies with much more population are needed for the clinical application of the treatment method.
If the tinnitus patient insists that he/she has no tinnitus symptom with respect to the tinnitogram, then there is no other alternative way to check and confirm the condition. In animal tests, some models have been developed to find the occurrence of tinnitus, but the experiments were just at the laboratory level through the regulated conditioned reflexes. For humans, there is no way to freely measure the aberrant neural signal, which is considered as the true nature of tinnitus yet. On the contrary, if the non-tinnitus patient insists the presence of tinnitus, the repeated measurements of tinnitus could be the referential evidences just like the diagnosis of hearing loss, but this could not be the conclusive evidence either due to insufficient objective confirmation just like the auditory evoked response test for hearing loss.
In order to diagnose the presence of tinnitus through the repeated tinnitogram, tinnitus was virtually set up with relatively lower frequency and higher loudness in the non-tinnitus group than the real tinnitus group. The repeated tinnitogram result showed statistically significant differences in the tinnitus loudness amongst each test. Therefore, it is considered that the repeated tinnitogram about loudness can enhance the accuracy of the tinnotogram and provide a useful reference to infer the presence of tinnitus.
Conclusion
The repeated tinnitogram helps to acquire the information on patient's tinnitus and infer the presence of tinnitus.
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