[Changes in otoacoustic emission during the glycerol test in the ears of patients with Meniere's disease].

Monitoring of cochlear function is one proposed clinical application of otoacoustic emission (OAE). To determine the clinical utility of OAE in monitoring, we studied changes in OAE during the glycerol test used to diagnose endolymphatic hydrops. Transiently evoked OAE (TEOAE) and distortion product OAE (DPOAE) were measured before and 3 hours after oral administration of glycerol in 22 ears of patients with Meniere's disease. The positive result in the glycerol test was observed in 11 of 22 ears. TEOAE was recorded using a nonlinear click stimulus, and total echo power (TEP) of the whole response and filtered echo power (FEP) of its mid-frequency (1000-2000 Hz) component were used as TEOAE parameters. The growth functions of DPOAE were recorded at 3 F2 frequencies--1000, 1500, and 2000 Hz. Changes in the growth function were determined based on changes in 2 parameters--maximum level and detection threshold of DPOAE. When changes in these 4 parameters exceeded 2 standard deviations above mean test-retest variability determined from OAE data for 17 normal ears, they were considered significant. Significant changes indicating improved cochlear function in 4 OAE parameters or the appearance of OAE during the glycerol test were judged positive for OAE. Regardless of glycerol test results, positive findings were observed in both OAEs whenever a pure-tone threshold at 1000 or 2000 Hz improved. However, even in ears for which pure-tone thresholds at these frequencies did not improve, both OAEs frequently exhibited positive findings. In all ears with a positive result in the glycerol test, positive findings were observed in DPOAE, but not in TEOAE. Of the 2 parameters of TEOAE, FEP always exhibited a positive finding in ears with a positive TEP finding and FEP positivity was higher than that of TEP. In DPOAE, no cases showed a positive finding only at F2 = 2000 Hz, and DPOAE at F2 = 1000 Hz could not be detected in 4 ears due to high noise floor. Overall, positive findings were obtained in 14 ears (63.9%) for TEOAE and 20 ears (90.9%) for DPOAE. In only 1 ear were no positive findings observed in either OAE. The sensitivity of OAE measurement as a diagnostic test for endolymphatic hydrops was higher than that of pure-tone audiometry. Of the 2 OAEs, test sensitivity was much higher for DPOAE than for TEOAE. These results show that OAE measurement detects changes in cochlear function during the glycerol test more sensitively than pure-tone audiometry. They also suggest that FEP is a better indicator than TEP as a parameter of TEOAE, and that DPOAE measurement at F2 = 1000 and 1500 Hz is sufficient for practical clinical use. However, of the 2 OAEs, DPOAE was considered more appropriate than TEOAE for monitoring during the glycerol test because of its high sensitivity in detection of changes in cochlear function. In conclusion, clinical use of OAE, especially DPOAE, as a test complementary to pure-tone audiometry during the glycerol test is very useful and will improve the diagnosis of endolymphatic hydrops.

Evaluation of radiological examination for sensorineural hearing loss.

The accuracy of radiological examinations has improved and their diagnostic ability has markedly increased. However, the cost of such examinations has also recently become an issue. In this study, the clinical significance of radiological examinations for sensorineural hearing loss (SNHL) was evaluated and the value of their utilization was reconsidered. A total of 1,276 ears of 724 patients who demonstrated unilateral or bilateral SNHL was studied retrospectively. Findings of radiological examinations such as plain X-ray (X-p), computed tomography (CT) and magnetic resonance imaging (MRI) of the brain or the temporal bone were investigated. Temporal bone X-p was usually performed to rule out acoustic tumors (AT). CT was further performed in 119 patients (16.4%) and MRI in 84 patients (11.6%) in total. The reasons or symptoms for further examination such as CT or MRI were X-p findings or auditory symptoms suspicious for AT or vertigo/dizziness suspicious for intracranial disease. Of five causes with AT, two with a small tumor exhibited normal findings for the internal auditory canal on temporal bone X-p. These small ATs were finally confirmed by MRI. MRI could also detect lacunar infarctions, cerebral atrophy and high jugular bulb which might be related to SNHL. These findings confirmed that MRI is very useful for detecting small ATs and suggested that MRI also reveals cerebral vascular insufficiency in patients with SNHL.

Sound lateralization and speech discrimination in patients with sensorineural hearing loss.

Sound lateralization and speech discrimination abilities are both closely related to central auditory system function. In this study, we investigated the relationship between sound lateralization and speech discrimination in patients with sensorineural hearing loss (SNHL) of unknown aetiology or presbycusis. Interaural intensity difference (IID) and interaural time difference (ITD) discriminations were measured using a self-recording apparatus for dichotic sound presentation, and the means of bilateral maximum scores in speech discrimination tests were calculated. Subjects with normal sound lateralization had good speech discrimination scores above 70%, while those with abnormal sound lateralization had poor scores below 70%. Some patients, however, had good speech discrimination but abnormal sound lateralization. These findings were obtained in both IID and ITD discrimination tests. Furthermore, some subjects could not discriminate ITD, although all could discriminate IID. These findings suggest that sound lateralization ability may be affected more than speech discrimination in SNHL of unknown aetiology or in presbycusis.

Patterns of change in growth function of distortion product otoacoustic emissions in Menière's disease.

The patterns of change in the growth function of distortion product otoacoustic emissions (DPOAEs) associated with hearing improvement in six patients with Menière's disease were investigated. The growth functions of 2F1-F2 DPOAEs at F2 frequencies of 1001, 2002 and 4004 Hz (DP-1, DP-2 and DP-4, respectively) were measured with F2 intensities ranging from 70 to 37 dBSPL in 3-dB steps. The F1 intensity was maintained 10 dB higher than the F2 intensity. The growth function was paired with the hearing threshold at the corresponding F2 frequency, and the relationships between changes in DP-1, DP-2 and DP-4 and those in hearing thresholds at 1, 2 and 4 kHz, respectively, were also investigated. The patterns of change in the growth function associated with hearing improvement could be classified into five types. In the first type, the DPOAE growth function became detectable, while the remaining four types were distinguished by combinations of changes in DPOAE amplitudes for lower and higher primary intensities. Multiple parameters, such as maximum amplitude and detection threshold of the growth function, appeared to be required for simple detection and discrimination of these patterns of change. It was also found that the DPOAE growth functions clearly changed in some cases even though the hearing thresholds did not change significantly at the corresponding F2 frequencies. This finding suggests that DPOAE growth function measurement can detect small changes in cochlear function which do not lead to changes in hearing threshold, and has higher sensitivity than pure tone audiometry in monitoring of cochlear function. In conclusion, our findings suggest that measurement of the DPOAE growth function is useful for monitoring cochlear function, and that information on its patterns of change is clinically important and useful.

Changes in distortion product otoacoustic emissions from ears with Menière's disease.

To investigate changes in distortion product otoacoustic emissions (DPOAEs) associated with hearing improvement in ears with Menière's disease, four parameters were studied. These were: DPOAE amplitudes for a moderate (L1/L2 = 65/55 dBSPL) and a high (L1/L2 = 74/64 dBSPL) primary level (65/55-DP and 74/64-DP amplitudes, respectively); maximum level of DPOAE amplitudes in the growth function (maximum DP level); and DPOAE detection threshold (DP threshold) of the growth function. Significant correlations were found between all four parameters and hearing threshold, except for the 65/55-DP amplitude at 1 kHz, and each parameter appeared to reflect the hearing threshold to some extent. However, the changes in the four parameters associated with hearing improvement were somewhat complicated. Changes could not be evaluated due to lack of detection of responses when the hearing thresholds exceeded 50 dBHL. Findings that parameters became detectable, the DP amplitude or the maximum DP level increased significantly, or the DP threshold lowered significantly were classified as "improved" findings. The number of ears with "improved" findings was larger for the maximum DP level or the DP threshold than for the 65/55-DP and 74/64-DP amplitudes in ears with a 10 dB or greater improvement in hearing threshold at the corresponding F2 frequency. Furthermore, a significant decrease in amplitude was found in some ears, although the hearing threshold was not elevated when the 65/55- or 74/64-DP amplitude was used as a parameter. On the other hand, "improved" findings for the maximum DP level or the DP threshold were observed for a relatively large number of ears without a significant change in hearing threshold, and it was thought that small changes in cochlear function which did not lead to changes in hearing threshold were detected by changes in DPOAEs. These findings suggest that parameters determined from the growth function, such as maximum DP level and DP threshold are better indicators for monitoring cochlear function than is DPOAE amplitude for a single primary level, and demonstrate the usefulness of the growth function measurement for monitoring purposes. Furthermore, evaluation by changes in the overall growth function using combined parameters appeared to increase sensitivity in detection of subtle changes in cochlear function. In conclusion, DPOAE measurement can be a useful examination for clinical monitoring of cochlear function in Menière's disease when the growth function is measured.

Frequency analysis of evoked otoacoustic emissions in Meniére's disease.

Our study was designed to establish a diagnostic significance in Meniére's disease by means of evoked otoacoustic emissions (EOAEs). EOAEs were recorded from patients with Meniére, and the "main frequency" of the emissions, which shows the maximum peak in the frequency spectrum, was examined as a variable. The main frequencies in ears with Meniére ranged mainly from 0.8 kHz to 1.1 kHz and were to be found at lower frequencies than in ears with normal hearing whose range was mainly from 1.0 kHz to 1.6 kHz. Furthermore, in some ears with Meniére, the main frequencies changed from lower to higher after administration of osmotic diuretics such as glycerol or isosorbide. On the basis of these results it was speculated that in ears with Meniére, lower frequency dominant emissions might be elicited by modification of the basilar membrane in endolymphatic hydrops and that the main frequencies might change from lower to higher with reduction of endolymphatic hydrops induced by osmotic diuretics. It was considered that the EOAE testing might be useful for a diagnosis of endolymphatic hydrops in Meniére.