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Audiometric Tests in Tinnitus Management

 


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The typical workup for tinnitus patients includes a medical examination, an audiometric assessment, a tinnitus evaluation and finally management of the patient.

The means of managing the patient can involve drug therapy, biofeedback or masking. However, regardless of the treatment of choice, most patients undergo, at least to some degree, parts of the three initial evaluations.

Our task is to describe, in part, the use of the audiogram in managing the tinnitus patient. The audiometric work-up for the tinnitus patient does not differ greatly from the typical audiometric assessment performed for diagnostic purposes or a hearing aid evaluation. This procedure includes pure tone testing (air conduction and bone conduction), impedance audiometry and speech testing. Special auditory tests are performed only when additional diagnostic information is indicated.

The only major difference in the procedure involves presenting pressure through the probe tip without the accompanying probe tone. This gives the clinician an indication as to whether or not atmospheric pressure changes might affect the patient's tinnitus. Some patients observe dramatic changes in their tinnitus with variations in pressure. These changes can be in the form of either a reduction or an exacerbation of the tinnitus.

The use of pressure changes to alter tinnitus with selective patients is currently investigating. Initial results with this procedure are promising and need to be pursued. In addition to its diagnostic value, the audiogram also serves as the basic reference for intensity measures. Most tinnitus matches are made in terms of sensation levels rather than sound pressure levels or hearing levels.

This decision was made for two reasons. First, one is limited to certain discrete frequencies in terms of hearing level; and secondly, most pitch matches are made at non-discrete frequencies or with bands of noise. It is then very simple to refer back to the audiogram to determine the approximate level of the stimulus used. There is, of course, a very expedient way to overcome this problem and that is to make actual sound measurements with a probe microphone either at the entrance to the canal or near the ear-drum.

There is presently a tinnitus synthesizer being designed which would allow for this type of measure. The audiogram also allows for various measures of the different parameters related to tinnitus. For example, there is considerable controversy regarding the manner in which loudness measures of tinnitus are made.

If one reviews the literature regarding this parameter, it appears that, for most patients, the tinnitus is not very loud. Most studies indicate that the loudness of tinnitus is less than 10 db. Sensation level, however, these measures do not seem to correspond to the degree of distress that the patient is experiencing.

Many patients appear to be severely affected by the tinnitus and yet the measure of intensity is only 1 or 2 db. above their threshold. Why the disparity? Vernon (1976) addressed this problem early on in the masking program when he suggested that the distress a patient encounters may not be directly related to loudness or that loudness recruitment may be operating or that we may not be measuring loudness correctly. Certainly, another factor which makes one signal seem more annoying than another is the pitch of the sound.

The experience of high frequency pure tone signals is very annoying to listen to as compared to low frequency sounds. This may very well be the reason that we do not see many Meniere's Disease patients in the clinic. Most of these patients present complaining of a roaring type of tinnitus which is generally found to simulate a low frequency band of noise that does not seem as bothersome as a high pitched sound.

In an attempt to determine what might be responsible for the disparity between the loudness of tinnitus and the amount of distress that the patient seemingly was exhibiting, we undertook a study at the University of Denver to investigate this relationship.

Two groups of patients were studied. The first group consisted of nine subjects with high frequency hearing losses and tinnitus, while the second group which was used for control purposes did not experience tinnitus and had normal hearing sensitivity. Of these 9 subjects, 5 had bilateral tinnitus and 4 had unilateral tinnitus. Thus, the total number of ears with tinnitus was 14. The loudness of the tinnitus was measured in two different ways.

The first method involved the traditional process whereby the tinnitus was matched to an external sound in the opposite ear. This procedure was accomplished by introducing the test tone at the frequency selected during the pitch match. The second method of establishing the loudness of the tinnitus involved matching the tinnitus to a normal frequency in the same ear. This procedure was very similar to the monaural loudness balance technique used for making loudness balance measures except that the tinnitus serves as the fixed reference stimulus to be matched. This method was labelled the proposed method.

The results of this experiment indicated that all fourteen ears showed greater differences in sensation level for the proposed method than for the traditional method. The mean scores for the two groups revealed a 6-6 db. SL for the traditional method and a 23.9 db. SL for the proposed method, or a mean difference of 17.3 db. This difference is almost four times as great for the proposed method as for the traditional method. Individual scores varied by as much as 30 db.between the two methods.

This difference was significant at the .001 level of confidence. When one reviews the differences between the two methods, the proposed method appears to be a more valid procedure than the traditional method in that the results of the proposed method seem more realistic with respect to the amount of distress the tinnitus patient appears to exhibit.

Furthermore, in the proposed method, the loudness of the tinnitus is being compared to a normal frequency and not a pathological frequency. All of the patients in the study showed recruitment on the basis of the MLB test. Therefore, it is highly likely that the small magnitudes of loudness which have been reported previously are due to the method of measurement and the fact that the external signal was presented at a frequency where the hearing was sufficiently depressed and the ear was recruiting. In such a case, the loudness of the external signal would increase rapidly above threshold and the perceived loudness reading on the dial would be considerably less than indicated. There is, of course, also the possibility that the tinnitus itself is recruiting.

To determine whether or not this is, in truth, the case, reaction time measurements were made to determine the loudness growth of the tinnitus itself. Reaction time measures have been suggested as a means of measuring recruitment (Moody, 1970; Chocholle, 1940). Vernon (1976) has proposed that reaction time measures could be used for this purpose to determine if the tinnitus was recruiting. That is, if the reaction time at the tinnitus frequency was considerably shorter than the reaction time at a non-tinnitus frequency, it would seemingly indicate that the tinnitus was recruiting and was being perceived as a much louder signal than was measured on the dial.

To investigate this phenomenon, reaction times to pure tones were obtained for the same nine patients utilized previously for the loudness study. These patients were tested at the tinnitus frequency, at a pathological non-tinnitus frequency and at a frequency where the hearing was normal. Three measures of reaction time were made: (a) at the tinnitus frequency; (b) at a frequency which revealed no hearing loss; and (c) at a non-tinnitus pathological frequency. For the purposes of control, the same measures were made for a comparable group who did not have tinnitus.

The results of the study revealed that for the experimental group, the reaction times were significantly shorter at the tinnitus frequency than at the other two frequencies. Such was not the case for the control group. Therefore, it seems reasonable to conclude that the tinnitus itself is probably recruiting and it further substantiates that loudness measures are indeed suspect. Perhaps the most common use of the audiogram with reference to tinnitus patients involve its use in the management of the tinnitus patient. The first consideration which is the primary determinant in managing the tinnitus patient relates to the associated hearing loss. The method of treatment may be quite different for those with hearing loss as opposed to those who do not have a loss.

This difference will be manifested mainly in the choice of instrument used to provide relief for the patient. Three different types of units are used to offer relief for tinnitus patients: (a) hearing aids; (b) tinnitus maskers; and (c) tinnitus instruments. If the patient has normal or near-normal hearing, the choice of instrument is a tinnitus masker. However, if the patient has sufficient hearing loss to require amplification, a hearing aid or a tinnitus instrument (a combination of an amplifier and a masker) is selected. The choice between the two units is based upon many different variables: (1) the amount of distress the patient is experiencing, (2) the patient's ability to sleep, (3) the amount of residual inhibition and (4) the degree to which they can be masked. These instruments are fitted with the proper molds, either monaurally or binaurally, depending upon the need.

The final purpose for the audiogram relates to the effect of long-term masking on the hearing sensitivity of the patient wo can also suffer from meniere's disease . Although considerable effort has been made to design maskers whose output do not exceed the damage risk criteria, there is still concern that the long range use of these instruments may cause some loss of hearing. Therefore, an audiometric examination prior to fitting the unit is necessary to establish a baseline audiogram. This audiogram will allow for annual comparisons to be made to determine any change in the threshold of the patient over a period of years.

In conclusion, there are numerous reasons which could be discussed regarding the use of audiometric findings for tinnitus patients. However, time does not allow for further expansion in this area. Let us conclude by reiterating the fact that the audiometric evaluation is an integral part of the tinnitus work-up and careful attention should be directed towards it.

You can read more about tinnitus and meniere disease treatment here: http://www.menieresdisease-treatment.com

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