Tinnitus complaint
A patient presenting a chief complaint of tinnitus poses an interesting problem to the clinician. Since tinnitus is a symptom and not a disease, physicians job as diagnosticians is to determine if the tinnitus is associated with hearing loss and to screen for retro-cochlear involvement.
Hospital examination
At hospital, a patient with tinnitus is examined like any other patient. A thorough history is taken and a complete audiologic and otologic evaluation is done.Patients are then referred for brain-stem-evoked response audiometry (BSERA).
Patients are referred if they have unilateral hearing loss, unilateral or bilateral tinnitus, tinnitus uncorrelated with hearing loss, meniere disease, vestibular complaints, asymmetric hearing loss, and progressive hearing loss. In addition, screening X-rays and /or blood tests might be ordered.
Tomograms of the temporal bone are taken to screen for the presence of a space-occupying lesion in or around the internal auditory meatus. Blood studies are done, for example, to test blood-sugar levels, thyroid function, or to screen for venereal disease. The history is taken with a view to determining a possible etiology for the tinnitus.
Audiological evaluation
The audiological evaluation includes standard pure-tone and speech audiometry, tone decay, 500 Hz. masking level difference and impedance audiometry including acoustic reflex decay. Adult and pediatric patients were tested during a year and a half. For these patients, both BSERA data as well as other central test data are available.
Six cases were chosen to illustrate (1) the considerable diversity of configuration of hearing loss and neurological symptoms experienced by the tinnitus case; and (2) how cases with nearly identical standard audiometric data and the complaint of tinnitus can exhibit very different findings for BSERA and other central tests. In each case, the tinnitus was thought to be the result of a sensory or neural defect. In no case was the tinnitus the objective.
First case
The first case, is a 14-year-old girl with a stable unilateral high-frequency hearing loss in the left ear. Significant medical history includes measles and lead poisoning. No tone decay was evident at 500 or 2000 Hz. The alternate binaural loudness balance test (ABLB) at 2000 Hz. showed complete recruitment. For the left ear, the acoustic reflex was absent at 4000 Hz. and abnormal reflex decay was seen at 2000 Hz.
The BSERA at equal levels revealed latencies for Jewett wave 5 to be identical. Tomograms were unremarkable. This finding is in direct contrast to the next case.
Second case
A 13-year-old girl with a unilateral loss in the right ear. Significant history includes parental Rh incompatibility (Hemolytic disease of newborn) and delivery by emergency Cesarean section. Had this been a typical kern-icteric hearing loss, we would expect it to be bilateral. The acoustic reflex is absent at 4000 Hz. in the right ear. The BSERA at equal levels (absolute level and sensation level) shows latencies for the right ear to be clearly later than for the left ear.
Tomograms were normal. Since her hearing loss has been stable for seven years, the medical decision was to simply monitor her status with audiometry and BSERA at regular intervals.
Third case
A 9-year-old boy with a newly identified high-frequency loss in the right ear. There was no significant history. Speech discrimination for the right ear is poor. Acoustic reflexes were present bilaterally via both ipsilateral and contralateral stimulation. The BSERA shows latencies for Jewett wave V on the right side to be later than the left by 0-42 milliseconds. Tomograms showed both internal acoustic meati to be symmetric.
This patient will be followed closely at regular intervals.
Forth case
A 9-year-old man whose chief complaint was tinnitus and occasional dysequilibritim. Audiometrically, there is no difference between his data and those seen in the Third case, which shows a high frequency sensorineural loss. Speech discrimination in the left ear was poor. The suspicious was of an acoustic neuroma. No abnormal tone decay was evident at 500, 2000, or 4000 Hz. Radiological studies indicated no abnormality. Jewett waves 3 and 5 only were evident on the BSERA recording. Latencies for wave 5 were within 0.2 milliseconds for the two sides.
Fifth case
A 62-year-old woman presenting a chief complaint of tinnitus as part of meniere's disease. Additional complaints elicited upon questioning were occasional frontal headaches and light-headedness when rising in the morning. Blood pressure was normal. There was a long history of occupational noise exposure.
The audiogram showed normal hearing sensitivity bilaterally. Acoustic reflexes were present bilaterally via both ipsilateral and contralateral stimulation. There was no abnormal reflex decay. BSERA at equal hearing levels are shown for the two ears. Wave 3 occurs 0.42 milliseconds earlier in the left than for the right. Wave 5 occurs 0.3 milliseconds later for the left than for the right. This is a case in which the BSERA recordings are clear, yet results are equivocal.
How do we interpret these data? The decision was made to monitor the patient closely.
Sixth case
A 34-year-old woman with a five-year history of tinnitus. Audiometrically, there is no difference between her data and those seen in fifth case above. The audiogram indicated normal hearing sensitivity. Acoustic reflexes were present bilaterally. The BSERA, at equal levels for the two sides, shows identical latencies for Jewett waves 3 and 5.
Comparing these findings with the previous cases, we find no differences on the basis of standard audiometric information alone, yet the first case showed a slight inter-aural latency discrepancy for the BSERA. The post hoc analysis of our data pool was simply an attempt to determine if 'routine' tests were in any way uniquely sensitive to the tinnitus complaint.
The usefulness of BSERA
Furthermore, we questioned the usefulness of BSERA as a differential diagnostic tool in these cases. Since tinnitus is only a symptom, this question cannot be approached in quite the same manner as the usefulness of BSERA, for instance, in the detection of acoustic tumors. BSER A has been useful in a wide range of cases for both adults and children. However, we do have tinnitus cases where normal BSERA was not confirmed by radiological studies.
We must ask whether or not the abnormal BSERA is a very early indication of a retro-cochlear lesion, or have we stumbled upon another unknown problem to which BSERA is rather sensitive?
Especially in those few cases in which there is no hearing loss, and in which tinnitus was the only symptom, would this unknown problem be related to that giving rise to the tinnitus?
One obvious problem is using BSERA as a tool to study tinnitus arises from the nature of the tool itself, at least as we routinely use it. A full complement of Jewett waves is evident only a moderate-to-high levels of stimulation. We might expect the tinnitus to actually be masked by the test stimulus in many cases. At levels low enough for the stimulus to mask the tinnitus in loudness, only wave 5 is typically present and not as stable and well defined as at higher levels.
When hearing loss is involved, one is always working at a relatively high level compared to normal hearing thresholds. In the unusual case of the patient with normal hearing and abnormal BSERA, we again must ask if a disease exists that can cause an alteration In the timing of neural signals transmitted in the central nervous system and yet not lead to obvious hearing loss.
It might be postulated that, were we to scrutinize enough such cases, we might find a preponderance of tinnitus and thereby have an instance in which BSERA was selective for tinnitus. Comparisons between such cases and those with normal BSERA and no complaint of tinnitus could prove most revealing.
Không có nhận xét nào:
Đăng nhận xét