CAOHC Newsletter: UPDATE
How
Tinnitus and Other Factors Contribute to Unreliable Noise-Induced
Hearing Assessment
by Peter C. Weber, MD, Medical University of South Carolina
Performing a basic pure-tone hearing test appears, at first glance, to be a simple, straightforward procedure, and is, with many patients. However, there are several factors that may be encountered, which if not noticed, may invalidate the test results. The following discussion will identify some of the most common sources of test unreliability. Suggestions for the examiner are offered that can improve test reliability and validity, and when the patient should be referred for a follow-up evaluation to the appropriate professional with more expertise.
Temporary threshold shift (TTS). TTS is a temporary loss of some hearing caused by exposure to loud noise (in excess of 90 dB) for one or more hours. The amount of TTS and how long it takes for hearing to recover depends on the level of the noise and the length of exposure. Along with hearing loss is a ringing type sound in the ear called “tinnitus.” To assure that the hearing test is representative of the patient’s true hearing and not inflated by TTS, the examiner should ascertain that the patient has not been exposed to loud noise for at least 16 hours before the hearing test.
Tinnitus. This a symptom that could be due to a variety of causes such as: stress to the ear as in the case of TTS from noise exposure, permanent hearing loss, ear infections, certain medications, hypertension, and brain lesions. The overwhelming most common reason for tinnitus is damage to the ear from noise exposure resulting in hearing loss.
The problem tinnitus presents when performing a hearing test is that the patient may have trouble differentiating the test tones from their tinnitus when they are similar in pitch. Thus, some hearing thresholds may appear to be better or worse than they really are due to confusion between the tinnitus and test tone. If the patient reports that he is having difficulty with the test because of tinnitus, first, make certain that the tinnitus is not caused by exposure to noise immediately before the test. If the patient was recently exposed to noise, the hearing test should be rescheduled. If the tinnitus is chronic, there is a simple way to minimize its effects on the hearing test. The patient should be instructed that the tone will be presented in a certain pattern, such as in groups of three short bursts, and they should make sure that they hear the full pattern before responding. If the patient begins imagining that they are hearing the pattern, indicated by an increase in the number of false responses, the pattern should be changed.
Malingering. Occasionally, a patient will purposefully exaggerate their inability to hear for a variety of reasons. It is important to recognize when a hearing evaluation is invalid due to malingering. Some common indicators of malingering are: a substantial change in hearing since the last test; inconsistent responses during the hearing evaluation; and ability to hear conversation much better than the audiogram would indicate. If the validity of the hearing test is suspect, the patient should be retested on a later date or referred to a facility with expertise in testing difficult patients.
Findings that warrant referral for further testing. The following conditions may indicate a serious problem and the patient should be referred for further medical evaluation:
- Actively draining ear.
- Sudden or rapidly progressive hearing loss in one or both ears.
- Unilateral hearing loss of recent onset that has not been evaluated.
- Conductive hearing loss greater than 15 dB.