On a possible prognostic value of otoacoustic emissions: a study on patients with sudden hearing loss

Assessment of Peripheral and Central Auditory Processing after Treatment for Idiopathic Sudden Sensorineural Hearing Loss

Introduction  When cases of idiopathic sudden sensorineural hearing loss (SSNHL) are treated successfully, most clinicians assume the normality and symmetry of the auditory processing. This assumption is based on the recovery of the detection ability on the part of the patients, but the auditory processing involves much more than detection alone. Since certain studies have suggested a possible involvement of the central auditory system during the acute phase of sudden hearing loss, the present study hypothesized that auditory processing would be asymmetric in people who have experienced sudden hearing loss. Objective  To assess the physiologic and electrophysiological conditions of the cochlea and central auditory system, as well as behavioral discrimination, of three primary aspects of sound (intensity, frequency, and time) in subjects with normal ears and ears treated successfully for SSNHL. Methods  The study included 19 SSNHL patients whose normal and treated ears were assessed for otoacoustic emissions, speech auditory brainstem response, intensity and pitch discrimination, and temporal resolution in a within-subject design. Results  The otoacoustic emissions were poorer in the treated ears compared to the normal ears. Ear- and sex-dependent differences were observed regarding otoacoustic emissions and pitch discrimination. Conclusion  The asymmetrical processing observed in the present study was not consistent with the hearing threshold values, which might suggest that the central auditory system would be affected regardless of the status of the peripheral hearing. Further experiments with larger samples, different recovery scenarios after treatment, and other assessments are required.

Otoacoustic emissions value in patients with idiopathic sudden sensorineural hearing loss

Objectives

This study aimed to determine the prognostic value of otoacoustic emissions (OAEs) in idiopathic sudden sensorineural hearing loss patients.

Methods

The study included 30 subjects with unilateral idiopathic sudden sensorineural hearing loss (ISSNHL). Each patient was evaluated four times: at baseline and after one week, one month, and three months of treatment. During each visit, each patient was subjected to full audiological history, otoscopic examination, basic audiological evaluations, and transiently evoked and distortion product otoacoustic emission (TEOAEs & DEOAEs).

Results

The hearing thresholds (frequency range 250–8000 Hz) and word recognition scores of patients with detectable TEOAEs and DPOAEs improved significantly, whereas no significant improvements were observed in those with no response.

Conclusion

Hearing improvement is better in patients with detectable TEOAEs and DPOAEs. As a result, TEOAEs and DPOAEs are recommended as routine tests in all SSNHL patients to predict outcomes and monitor treatment as TEOAEs and DPOAEs reflect the cochlear OHCs activity.

Analysis of the relationship between changes in the auditory brainstem response and prognosis in patients with sudden hearing loss

Objective

To analyse how the auditory brainstem response changes in patients with sudden sensorineural hearing loss.

Method

Data were collected via retrospective medical chart review.

Results

Forty-three patients were included in this study. The mean latency of auditory brainstem response wave 1 was significantly longer for the affected side than for the unaffected side (p = 0.003). The mean latency of auditory brainstem response wave 1 was significantly shorter, and the mean amplitude of auditory brainstem response wave 1 was significantly larger, in the good response group compared to the poor response group. In forward conditional logistic regression analysis, auditory brainstem response wave 1 latency was an independent predictor of a good response (odds ratio = 34.37, 95 per cent confidence interval = 1.56–757.15, p = 0.025).

Conclusion

In patients with sudden sensorineural hearing loss, the latency of wave 1 of the auditory brainstem response was significantly increased and was related to prognosis.

Diagnostics and therapy of sudden hearing loss

This article reviews recent aspects of diagnostics, differential diagnostics, and evidence in systemic and local therapy of idiopathic sudden sensorineural hearing loss (ISSHL). Since a number of disorders can be accompanied by sudden hearing loss, a meaningful and targeted diagnostic strategy is of utmost importance. An important differential diagnosis of sudden hearing loss are intralabyrinthine schwannomas (ILS). The incidence of ILS is probably significantly underestimated. This may be due to the lack of awareness or lack of explicit search for an intralabyrinthine tumor on MRI or an inappropriate MRI technique for the evaluation of sudden hearing loss ("head MRI" instead of "temporal bone MRI" with too high slice thicknesses). Therefore, the request to the radiologist should specifically include the question for (or exclusion of) an ILS. With special MRI techniques, it is possibly today to visualize an endolymphatic hydrops. The evidence in the therapy of ISSHL is - with respect to the quality and not quantity of studies - unsatisfying. The value of systemically (low dose) or intratympanically applied corticosteroids in the primary treatment of ISSHL is still unclear. In order to investigate the efficacy and safety of high dose corticosteroids as primary therapy for ISSHL, a national, multicenter, three-armed, randomized, triple-blind controlled clinical trial is currently performed in Germany (http://hodokort-studie.hno.org/). After insufficient recovery of the threshold with systemic therapy of ISSHL, intratympanic corticosteroid therapy appears to be associated with a significantly higher chance of an improved hearing threshold than no therapy or placebo. Both, hearing gain and final hearing threshold, however, appear to be independent from the onset of secondary therapy. Based on currently available data from clinical studies, no recommendation can be made with respect to the type of corticosteroid and specifics of the intratympanic application protocol.

Current audiological diagnostics

Today's audiological functional diagnostics is based on a variety of hearing tests, whose large number takes account of the variety of malfunctions of a complex sensory organ system and the necessity to examine it in a differentiated manner and at any age of life. The objective is to identify nature and origin of the hearing loss and to quantify its extent as far as necessary to dispose of the information needed to initiate the adequate medical (conservative or operational) treatment or the provision with technical hearing aids or prostheses. Moreover, audiometry provides the basis for the assessment of impairment and handicap as well as for the calculation of the degree of disability. In the present overview, the current state of the method inventory available for practical use is described, starting from basic diagnostics over to complex special techniques. The presentation is systematically grouped in subjective procedures, based on psychoacoustic exploration, and objective methods, based on physical measurements: preliminary hearing tests, pure tone threshold, suprathreshold processing of sound intensity, directional hearing, speech understanding in quiet and in noise, dichotic hearing, tympanogram, acoustic reflex, otoacoustic emissions and auditory evoked potentials. Apart from a few still existing gaps, this method inventory covers the whole spectrum of all clinically relevant functional deficits of the auditory system.

Neuromagnetic index of hemispheric asymmetry prognosticating the outcome of sudden hearing loss

The longitudinal relationship between central plastic changes and clinical presentations of peripheral hearing impairment remains unknown. Previously, we reported a unique plastic pattern of “healthy-side dominance” in acute unilateral idiopathic sudden sensorineural hearing loss (ISSNHL). This study aimed to explore whether such hemispheric asymmetry bears any prognostic relevance to ISSNHL along the disease course. Using magnetoencephalography (MEG), inter-hemispheric differences in peak dipole amplitude and latency of N100m to monaural tones were evaluated in 21 controls and 21 ISSNHL patients at two stages: initial and fixed stage (1 month later). Dynamics/Prognostication of hemispheric asymmetry were assessed by the interplay between hearing level/hearing gain and ipsilateral/contralateral ratio (I/C) of N100m latency and amplitude. Healthy-side dominance of N100m amplitude was observed in ISSNHL initially. The pattern changed with disease process. There is a strong correlation between the hearing level at the fixed stage and initial I/C_amplitude on affected-ear stimulation in ISSNHL. The optimal cut-off value with the best prognostication effect for the hearing improvement at the fixed stage was an initial I/C_latency on affected-ear stimulation of 1.34 (between subgroups of complete and partial recovery) and an initial I/C_latency on healthy-ear stimulation of 0.76 (between subgroups of partial and no recovery), respectively. This study suggested that a dynamic process of central auditory plasticity can be induced by peripheral lesions. The hemispheric asymmetry at the initial stage bears an excellent prognostic potential for the treatment outcomes and hearing level at the fixed stage in ISSNHL. Our study demonstrated that such brain signature of central auditory plasticity in terms of both N100m latency and amplitude at defined time can serve as a prognostication predictor for ISSNHL. Further studies are needed to explore the long-term temporal scenario of auditory hemispheric asymmetry and to get better psychoacoustic correlates of pathological hemispheric asymmetry in ISSNHL.

Short-term changes of hearing and distortion product otoacoustic emissions in sudden sensorineural hearing loss

OBJECTIVES

The function of outer hair cells can be measured objectively and noninvasively by distortion product otoacoustic emission (DPOAE). The aims of the study were to investigate the changes of DPOAE in the recovery course and to pursue the relationship between the changes of DPOAE and hearing improvement in patients with sudden sensorineural hearing loss.

STUDY DESIGN

: Retrospective case series review.

METHODS

Both DPOAE and pure tone audiometry were performed before 7 days after the onset and followed after 2 weeks in 40 patients with sudden sensorineural hearing loss. Patients were grouped on the basis of the initial hearing loss and the results of their recovery. All DPOAE amplitudes were analyzed at 2f1-f2, and DPOAE sum was calculated.

RESULTS

The initial DPOAE sum in ears with the initial mild-to-moderate hearing loss (hearing threshold, <or=55 dB) was not different from that in contralateral normal ears, but it was decreased or absent in ears with the initial moderately severe to profound hearing loss (hearing threshold, >55 dB) compared with that in contralateral normal ears. In ears with the initial moderately severe to profound hearing loss, the changes of DPOAE sum values positively correlated with the hearing improvement but not in ears with the initial mild-to-moderate hearing loss. Although the presence of initial DPOAE responses indicated good prognosis, the absence of initial DPOAE responses did not always indicate poor prognosis.

CONCLUSION

Our findings showed that the function of outer hair cells is relatively spared in ears with the initial mild-to-moderate hearing loss, and its recovery is not related to the hearing improvement; however, the function of outer hair cells is impaired in ears with the initial moderately severe to profound hearing loss, and the functional improvement of outer hair cells is important for hearing recovery. Clinical implications of our findings were discussed.

Evaluation of cochlear hearing disorders: normative distortion product otoacoustic emission measurements

OBJECTIVE

The overall objective was to begin the investigation, in humans, of distortion product otoacoustic emission measurements, which are intended to be part of a diagnostic protocol being developed. This protocol, designed to distinguish among different cochlear hearing disorders, has been tested to date only through lesion studies in the gerbil (Mills, Ear and Hearing, 27, 508-525, 2006). To be applied successfully to human subjects, it was required that parameters and procedures for emission measurements be found, which resulted in sufficiently small intersubject variability in normal subjects, among other requirements. To attain these objectives, measurements of particular otoacoustic emission responses were made in a reference group of young adults having excellent hearing.

DESIGN

Twenty young adults (age 18 to 24 yr; 40 ears) comprised the subject group, with equal numbers of men and women. Inclusion criteria included hearing thresholds of 10 dB HL or better in both ears at all frequencies (0.5, 1, 2, 3, 4, 6, and 8 kHz), plus a tympanometric peak response located within +/-30 daPa of ambient pressure in both ears. The otoacoustic emission stimulus consisted of two tones (frequencies f1 and f2) varied in level using 5-dB steps with the lower-frequency stimulus level always 10 dB greater than that of the higher-frequency stimulus. The emission isoresponse threshold was defined to be the stimulus level required to obtain an emission amplitude of -10 dB SPL. Another potential measure was defined to be the emission amplitude at the highest stimulus levels routinely tested. Mean emission amplitudes and thresholds were determined for f2 frequencies equal to audiometric frequencies from 1 to 8 kHz, using two different stimulus frequency ratios, f2/f1=1.21 and 1.28.

RESULTS

One result of the study was the derivation of reference standards for the emission threshold level, similar to the HL scale for pure-tone thresholds. For use in diagnosis, the optimal measure was found to be the otoacoustic emission threshold for the stimulus frequency ratio f2/f1=1.21 and for f2 frequencies from 1 to 6 kHz. The f2 frequency of 8 kHz seemed less useful because the emission had a relatively high mean threshold. For frequencies 1 to 6 kHz, the variances were adequately small: 95% of the emission thresholds fell within +/-13 dB of the mean at each frequency, a variability only slightly larger than that for the gerbil. Finally, even within the 10-dB HL limit, responses showed a slight trend for increased emission thresholds with increased auditory threshold. Only at 8 kHz was the amount of covariance important, however, with the relationship between emission and auditory thresholds strongest for men.

CONCLUSIONS

Emission reference standards can be developed by testing a group of young adults with excellent hearing. The diagnostic procedure previously proposed on the basis of gerbil lesion studies may be adapted with relatively little modification for use in human subjects. However, validity of the test and specific numerical results for human subjects remain to be firmly established for the purpose of distinguishing among different cochlear disorders.