Audiologic Diagnosis of Central versus Eighth Nerve and Cochlear Auditory Impairment

122 subjects divided into four groups according to the site of lesion (cochlea, eighth nerve, brainstem and temporal lobe) were subjected to an audiometric test battery, including pure-tone sensitivity measures, recruitment testing, tone decay, Békésy audiometry, speech audiometry, stapedius reflex measures and auditory brainstem response (ABR) audiometry. The results were contrasted among the four groups by calculating several measures of test performance, including sensitivity, specificity, efficiency, A' (test performance) and plots on the receiver operating characteristic (ROC) space of pure positives versus false alarms. In the differential diagnosis between eighth nerve and cochlear site, the various measures did not rank the tests in the same order: (a) for efficiency: ABR, Békésy audiometry; (b) for A' (similarly to the analysis into the ROC space): ABR, recruitment, Békésy, stapedius reflex, speech audiometry, tone decay. In distinguishing an eighth nerve from a brainstem site, it is important to consider amount of hearing loss, presence of tinnitus, abnormal tone decay and Békésy audiometry patterns. ABR adds significant diagnostic efficiency only when waves II, III and V are detectable: a prolonged I–II interpeak interval (IPI) and a normal III-V IPI are characteristic of the eighth nerve site. ABR gives good diagnostic support in the intrinsic brainstem lesions by suggesting changes in the generator sites of the component waves. The audiometric diagnosis of temporal lobe lesions involving the auditory cortex still relies upon speech audiometry: tests specifically designed for this purpose by Bocca and Calearo and by Jerger - i.e. the 'sensitized sentences' and the identification of synthetic sentences under ipsi- or contralateral competing message - are commendable for their sensitivity and efficiency in distinguishing brainstem from temporal lobe sites. In brainstem sites, the most affected ear is ipsilateral to the lesion for ABR, but contralateral for speech audiometry.     

Quantitative interpretation of audiological test battery. I. A comparison with ABR in 97 cases of unilateral sensorineural hearing loss

A retrospective study was made of 97 patients with unilateral sensorineural hearing loss who underwent an audiological test battery and ABR during a 2 1/2-year period. The test battery included tone- and speech audiometry, Békésy audiometry, loudness balance test, tone decay test and impedance measurements (reflex thresholds and reflex decay). A quantitative interpretation of each audiological test was tried out and a mean value of included tests (audiological test score ATS), was compared with results of ABR. The audiological test score showed the same predictive value as ABR for detection of acoustic neurinomas. Among the auditory tests, Békésy audiometry had the lowest sensitivity. Eight patients with neurinomas were found in the series. Retrocochlear test results prevailed in another 23 ears, most often in combined hearing loss and vestibular dysfunction and in insidious or longstanding hearing loss. Quantitative interpretation of the audiological test battery is valuable for uniformity in classification of sensorineural hearing loss, and will facilitate extended studies on aetiology and course in auditory dysfunction.     

Audiologic evaluation of patients with localized intracranial lesions.

A battery of audiological tests for retrocochlear disorders was performed of 79 cases with localized intracranial lesions confirmed surgically or neurologically. The Type III trace of Békésy audiometry was found to originate from pathologies in the brainstem and the Type IV from abnormalities in the first neuron of the VIIIth nerve or in the brainstem. It was suggested that an unusually large amplitude peak in the Békésy tracing indicates a lesion in the temporal lobe. Large values of differential limen for short increment (DLSI) were found in patients with brainstem lesions. A good speech discrimination with a poor filtered speech discrimination apparently indicated supratentorial lesions. The binaural separation test using dichotically presented digit sounds was found to be helpful for differential diagnosis between the supratentorial and subtentorial lesions.     

Study on the hearing impairment in diabetic patients

In order to accurately evaluate the quality and quantity of hearing loss in diabetics and to identify the site of the lesions, Békésy audiometry, impedance audiometry with stapedius reflex test, speech discrimination and electrocochleography and brainstem auditory evoked potentials were performed in 43 patients with diabetes mellitus. The results were compared with those of 43 sex- and age-matched non-diabetic subjects. The results showed that the average acoustic thresholds and AP reactive thresholds were significantly elevated in diabetic subjects as compared with those in the controls. There was a significant decrease in mean PBmax% in the diabetic group. The incidence (48%) of hearing impairment in diabetics is higher than that (10%) in controls. The diabetic hearing impairment is characterized by bilaterally symmetrical high tone sensorineural deafness.     

On the interpretation of Békésy audiograms (author's transl)]

A group of 112 subjects with sensorineural hearing loss was checked by an audiological test battery consisting of: pure tone audiometry, SISI Test, tone decay test and fixed frequency Békésy audiometry. Classification of Békésy tracings by two audiologists showes good agreement when introducing a hybrid type I/II, which completes Jerger's classification system of types I--IV. The results of our investigation exhibit no significant differences of manual pure tone threshold and automatic tracing contrary to some other authors. Finally the correlation of diagnosis and type of Békésy audiogram is discussed.     

Comparison of the hearing threshold measured by manual pure-tone and by self-recording (Békésy) audiometry.

The hearing threshold of 115 subjects aged 25--63 years and working on a shipyard were determined both by Békésy sweep audiometry and by conventional manual octave pure-tone audiometry at fixed audiometric frequencies. The attenuation rate was 2.5 dB s-1 with pulsed-tone presentation and the sweep time from 0.25 to 10 kHz was 400 s for the Békésy audiometer. Manual pure-tone audiometry was performed in 5-dB steps. The Békésy method gave the lowest values for the hearing thresholds. It has been possible to find a useful linear relation between pure-tone and Békésy hearing thresholds. With the help of a retest experiment, it has been established, that the standard deviations of hearing thresholds obtained under similar conditions in a pure-tone investigation are about twice as large as those obtained in a Békésy investigation.     

Reliability of Békésy threshold tracing in identification of carriers of genes for an X-linked disease with deafness

Seven identified carriers and 20 potential carriers of Norris's disease have been examined by pure tone octave audiometry and Békésy audiometry. The investigation supports earlier results of Békésy threshold tracings performed in heterozygote carriers of genes for recessive hearing impairment. The sensitivity of the method is poor. The specificity of the Békésy threshold tracing is high, meaning that an absent dip cannot exclude the possibility of a subject being a carrier, whereas a present dip can be regarded as an indication of carrier. When comparing conventional octave audiometry and Békésy threshold tracing, the latter method is found to be more subtle in finding carriers of genes for recessive deafness. Therefore, Békésy threshold tracing may be of help in the genetic counselling of potential carriers of genes for recessive deafness.     

Comparison between hearing threshold measurements made with and without the aid of an ear speculum

The hearing threshold levels of a small group of shipyard workers having differing degrees of hearing impairment were measured five times using the following audiometric techniques: fixed-tone Békésy audiometry with MX 41/AR cushions, fixed-tone Békésy audiometry with an ear speculum, and sweep-frequency Békésy audiometry with an ear speculum. From these data the mean standard deviations of the hearing threshold levels for the frequencies 0.5, 1, 2, 3, 4, 5, 6, 7 and 8 kHz were calculated, thus giving a measure of the accuracy of each method. The hearing threshold levels obtained by the three methods are compared, and the merits of data handling, expressing hearing threshold levels in pascals rather than decibels, are also discussed.     

Audiological investigation of chronic alcoholics

Pure tone audiometry performed on 67 alcoholics showed a sensorineural hearing loss in 70% of the ears examined. The prevalence of the hearing loss was related to the duration of heavy drinking. Twenty-two subjects with hearing loss were evaluated using impedance audiometry, SISI test, tone decay test and fixed frequency Békésy recording. The results of these tests are suggestive of a retrocochlear lesion in chronic alcoholics.     

Audiometric tests in gene carriers of Norrie's disease.

The purpose of the present study was to validate the reliability of audiometric testing procedures in the identification of carriers of Norrie's disease by using DNA analysis. Potential female carriers of Norrie's disease were investigated by means of Békésy tracing audiometry and stapedial reflex thresholds previously found to reveal carriers of recessively inherited hearing impairment by means of peculiar 'dips' and elevation in the thresholds. Relating the audiometric test results to the outcome of the DNA analysis the previous findings could not be confirmed. In addition no concordance between the two audiometric test procedures was demonstrated, and Békésy threshold tracing exhibited poor repeatability and sensitivity. It is concluded that none of these audiometric test procedures are feasible for detection of carriers of an X-linked hearing disorder, such as Norrie's disease.     

High-frequency Békésy audiometry. V. Excursion width

26 normally hearing young adults produced Békésy-type tracings for pure tones ranging from 7 to 19 kHz. Tones were pulsed (2.5/s) and delivered in the fixed-frequency mode. Chart rate (1 octave/min) and rate of attenuation (2.5 dB/s) were analogous to that typically used in clinical Békésy audiometry. Results indicated that subjects typically produced median excursion widths ranging from 5 to 15 dB. No systematic change in excursion width for conventional-frequency Békésy audiometry. The results of the present study were discussed regarding their utility in validation of responses to Békésy audiometry.     

Sensorineural hearing loss associated with hypoparathyroidism

The hearing loss of 21 patients with hypoparathyroidism was investigated by pure tone audiometry, short increment sensitivity index (SISI) test, Békésy audiometry, speech audiometry, and auditory brain stem response. Sensorineural hearing loss was found in 7 of 21 patients (13 of 42 ears) receiving no treatment for hypoparathyroidism or having chronic hypocalcemia. The high SISI score, presence of recruitment, and prolongation of the wave I (N1) latency suggested that the inner ear is responsible for hearing loss in these cases. Inner ear dysfunction was probably due to the low calcium level in inner ear fluid and/or the direct effect of vitamin D deficiency on the inner ear.     

The Audioscan: a high frequency resolution audiometric technique and its clinical applications

The Audioscan is a form of high definition audiometry based on iso-hearing level frequency sweeps, which was developed by Meyer-Bisch in 1990. Compared with traditional tone audiometry, it sweeps across the preset frequency range at a predetermined sweep rate and provides a continuous audiometric curve. Because the device has a maximum frequency range of 125-16 000 Hz with 64 frequencies per octave, the Audioscan method can, theoretically, give 64 times as many values as fixed-frequency audiometry, which may give greater accuracy and sensitivity. An advantage of this is its capacity to detect mild audiometric deficits such as narrow notches situated between the frequencies normally tested. These may represent very limited auditory lesions, at a stage when they cannot be detected by routine audiological methods. Thus, the Audioscan method can give not only a detailed audiometric curve, but also provide important indicators of mild auditory dysfunction. The Audioscan device (e.g. Essilor model) is commercially available for clinical purpose. It is a software-based system, which can also be used for pure tone audiometry and Békésy audiometry. This paper reviews the general aspects of the Audioscan technique and current applications for detecting auditory dysfunction. This would be valuable to provide some guidelines on the Audioscan assessment, and contribute to a clarification of the clinical application of Audioscan and facilitate further research.     

Functional hearing loss in speech audiometry (author's transl)

In a group of 238 patients assessed for medico-legal reasons, 26 subjects were found to have functional hearing problems. In detecting the presence of functional hearing loss, the reliability of speech audiometric patterns was shown. Each patient demonstrated at least one suspicious response. The evaluation revealed an irregular configuration of curves ("step-like", 56%) and a better understanding for monosyllabic testwords than for digits (28.8%) as the most important criteria. In the control group of 40 hard-of-hearing patients without functional hearing losses, testing-irregularities were found in only 2.5-3.7% of the patients. Furthermore, discrepancies between speech reception thresholds and pure tone averages (84.6%) as well as poor test-retest reliability in tone audiometry contributed to an identification of functional hearing loss. Békésy-audiometry Type V was obtained in 73% of those patients studied.     

Psychological aspects of psychogenic deafness in children

Twenty-nine children with psychogenic deafness were investigated from audiological and psychological aspects. ABR and Békésy audiometry were useful for diagnosing psychogenic deafness. The elapsed time from the start of treatment to audiometric recovery was significantly shorter in patients receiving psychological treatment, indicating that treatment by a team of otologists and counselors was able to hasten recovery in children with psychogenic deafness. The pattern of hearing recovery in the treated group was classified into 3 types and in the control group into 4 types. Counseling seemed to have a positive effect on patients with fluctuating improvement. In the patients in the treated group, the elapsed time to audiometric recovery from the beginning of psychological treatment was 7.5 months; however, in the control group recovery it took 17.1 months. Psychological treatment revealed that the clinical course of psychogenic deafness in children seemed to have some relation to the patient's personality and psychological stresses.     

Earmoulds: some benefits from horn fitting.

The narrow bore of conventional hearing aid earmoulds restricts the transmission of higher auditory frequencies. For subjects with moderate to severe high-frequency hearing loss this is likely to have an adverse effect on the perception and recognition of phonemes with high-frequency components. Twenty-two subjects with predominantly high-frequency hearing loss underwent a series of tests to compare the performance of earmoulds having conventional 1.9 mm through-tubing with earmoulds fitted with a smooth horn with a final internal diameter of 4 mm. The test battery comprised free-field Békésy audiometry, in-the-ear pressure measurement, speech audiometry using AB word lists and semantic differential rating of the relative sound quality of the two systems. Subjectively the horn fitting was rated as clearer, more natural, undistorted and acoustically comfortable. Objectively, by both Békésy audiometry and in-the-ear pressure measurement, the horn gave more gain in the higher auditory frequencies. With the horn there was improved recognition of phonemes, especially fricatives and affricatives.     

Early detection of hearing damage in young listeners resulting from exposure to amplified music

Sixty young subjects in the 15-23 age range, selected on the basis of a questionnaire on the degree of exposure to amplified music, underwent 'high resolution' (4 min per octave) sweep-frequency Békésy tracking audiometry, and measurement of auditory frequency resolution at 4 kHz using the psychophysical comb-filtered noise masking technique. The more exposed groups had 10-15% wider bandwidths than the least exposed, and this difference achieved significance when subjects having audiometric notches were excluded, or when a subset of exposed subjects was taken in whom subjective evidence was obtained of Temporary Threshold Shift or post-exposure tinnitus. While the most exposed groups did not show significantly greater averaged thresholds, there was in the older age group, a significantly increased prevalence of notches in the audiograms in the 3.5-6 kHz range. We conclude that exposure to amplified music can be harmful, the earliest sign being decrease in frequency resolution, and that early elevation of thresholds is better detected by high-resolution Békésy tracking (extending over the range 2-8 kHz) than by conventional fixed-frequency audiometry.     

Auditory adaptation and auditory fatigue

Twenty subjects without otological disease were examined for auditory thresholds by Békésy audiometry and by the Feldmann Test (Adaptogramm), before and after noise exposure to one ear of 90 db SPL at 3 kHz for 15 minutes. The exposed ear was also tested for hearing fatigue (TTS). There was no significant correlation between Békésy audiometry and Feldmann test curves or between these adaptation tests and the hearing fatigue test (TTS) after noise exposure. Our results suggest that these methods of measuring adaptation do not correspond, and that adaptation measurements, prior to noise exposure, have no predictive value for hearing fatigue test results following noise exposure. After noise exposure changes were found in the non-exposed ear which were manifested as variability of the Békésy audiometry curves and flattened Feldmann curves. We thought that these results might indicate a central adaptation following noise exposure. There was interference of this so called "central adaptation" with peripheral fatigue in the exposed ear.     

Stapedius reflex test, brainstem audiometry and opto-vestibular tests in diagnosis of acoustic neurinomas. A comparison of test sensitivity in patients with moderate hearing loss

The stapedius reflex test, brainstem audiometry and the opto-vestibular tests for identifying acoustic neurinomas (AN) were evaluated and compared in a study of 21 patients with radiologically or surgically verified AN and a pure tone average not exceeding 60 dB HL. The stapedius reflex test results were interpreted according to the criteria developed at this clinic. The stimuli for the auditory brainstem response (ABR) were 2 kHz haversine waves and 4 kHz square waves. The vestibular examination consisted of a caloric test and the recording of eye-tracking and gaze nystagmus. In the cases studied the stapedius reflex test gave 1 false-negative result and ABR none. The ENG gave 3 false-negatives whereas the results of speech discrimination tests were misleading in no fewer than 1/3 of the cases. The results of the different tests were directly correlated but correlation coefficients did not exceed 0.65. Tumours larger than 15-20 mm showed a different test pattern than those below that size: stapedius reflex response, ABR and caloric response were eliminated and all of these patients had abnormal optomotor function. It is suggested that an optimal routine test procedure should consist of a pure tone audiogram, supplemented by ABR or the stapedius reflex test. Opto-vestibular tests may be of value in a preliminary estimation of tumour size.     

Cochlear Findings in VIIIth Nerve Tumors

We have been particularly concerned with the large number of patients with confirmed retrocochlear lesions who have demonstrated cochlear test results on audiological evaluation. The literature is replete with information suggesting that the patient with a tumor of the VIIIth nerve will demonstrate the classical signs of significant reduction in auditory speech discrimination, abnormal tone decay, lack of loudness recruitment, negative SISI scored and Békésy tracings classifiable as either type III or type IV. We feel it is safe to say that one rarely encounters such a clearcut picture.

In this paper we discuss the audiologic data for a series of patients recently evaluated in our department. All these patients demonstrated only cochlear findings on audiological evaluation, yet all patients had surgically confirmed VIIIth nerve tumors.