Evoked otoacoustic emissions in differential diagnosis: a case report

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.

Auditory Efferent Function Is Affected in Multiple Sclerosis

OBJECTIVE

This study evaluated efferent medial olivocochlear (MOC) function in patients with multiple sclerosis (MS). Various afferent auditory abnormalities have been described in MS, but there is a paucity of data on efferent function. The brain stem is a site of predilection for MS plaques and the efferent MOC pathway may be affected at this level.

METHODS

The study included 30 patients who had normal hearing. According to MRI findings, they were divided into two groups: those with an identifiable brain stem lesion (n = 10) and those with MS lesions in other parts of the central nervous system but without demonstrable MS plaques in the brain stem (n = 20). MOC function was evaluated by the olivocochlear suppression test, using transient evoked otoacoustic emissions. All subjects underwent standard auditory tests, including pure-tone audiometry and recording of auditory brain stem evoked responses. Twenty-two healthy subjects with normal hearing, matched for age and gender, served as a reference group for the auditory data.

RESULTS

The results showed that 66.6% of all patients had reduced MOC function, particularly those (90%) with identified lesions of the brain stem on MRI. Furthermore, abnormal MOC function was found in 55% patients without evidence of a brain stem lesion on MRI.

CONCLUSIONS

This study provides the evidence for a deficit of efferent auditory function in the majority of patients with MS. Taking into consideration the possible roles of the MOC system in processing of auditory information, abnormal MOC suppression in patients with MS may explain a variety of auditory presentations that are currently largely overlooked. This study also highlights the diagnostic value of the MOC suppression test as a site-of-lesion diagnostic test in MS and in identifying subtle brain stem lesions undetected by MRI, suggesting that subtle brain stem lesions may exist and that the MOC suppression test is sufficiently sensitive to detect them. Accordingly, the MOC suppression test may provide a tool for an early diagnosis of MS.

Preserved otoacoustic emission in a child with a profound unilateral sensorineural hearing loss

We report a case of profound unilateral sensorineural hearing loss with good response of otoacoustic emission. The patient was a 5-year-old boy. who was diagnosed to have unilateral hearing impairment on pure tone audiometry at the first visit. The affected ear showed the absence of auditory brainstem response; however, its transiently evoked otoacoutic emission and distortion product otoacoustic emission were considered to be normal. These findings indicated that the outer hair cell of cochlea was not impaired and that the impairment should be localized between inner hair cells, primary afferent fiber or its synapses, spiral ganglion of the cochlea and acoustic fiber, or at a combination of these areas. That is, evaluation of otoacoustic emission was useful in determining the region of impairment in sensorineural hearing loss. Further follow-up will be necessary to differentiate the present case from auditory neuropathy.

Anomalous screening outcomes from click-evoked otoacoustic emissions and auditory brainstem response tests

Transiently evoked otoacoustic emissions (TEOAE) and auditory brainstem response (ABR) tests were used in parallel to screen 862 neonates with risk factors for hearing loss. Seven neonates (0.81%) passed on TEOAE screen yet failed on ABR in one ear (six neonates) or both ears (one neonate). This combination of results has been termed 'anomalous'. Examination of audiometric results obtained on follow-up shows that in one ear of one neonate the result was consistent with the later confirmed audiogram shape. The explanation for the anomalous results in the remaining ears is unclear although neural maturation and the effects of hyperbilirubinaemia are possibilities. There were no instances of progressive or retrocochlear hearing loss identified. None of the seven neonates had better ear hearing loss of > or = 40 dB on long term follow-up.

Diagnostic potential of distortion product otoacoustic emissions in severe or profound sensorineural hearing loss

To evaluate the potential of distortion product otoacoustic emissions (DPOAEs) in differential diagnosis of hearing loss, these were routinely measured in 232 ears of severe or profound sensorineural hearing loss. Normally recordable DPOAEs were found in 16 ears (8 patients) and the results were confirmed through retests after intervals; positive responses of transiently evoked otoacoustic emissions (TEOAEs) were additionally tested. The findings suggest that nerve deafness and hair cell deafness may be partly distinguishable.

Clinical applications of otoacoustic emissions in sudden hearing loss

Sudden hearing loss (SHL) is a controversial topic for which no definitive practical guidelines exist. Studies employing vasodilators, plasma expanders, anticoagulants, and carbogen inhalations have shown no improvement over the rate of spontaneous recovery. At present, there is insufficient evidence to support medical treatment for SHL, except steroid therapy in selected patients. Distortion product otoacoustic emissions (DPOAEs) are sensitive to cochlear disorders and are absent in ischemic injury to the cochlea, but can persist in cochlear neuritis. In a prospective study of 10 patients who presented to Albany Medical Center from 1995 to 1996, three patients with intact DPOAEs at presentation had an average improvement of 33 dB in the pure-tone average (PTA) of 0.5, 1.0, and 2.0 kHz with steroid therapy, whereas five of seven patients with absent DPOAEs had no improvement in hearing despite steroid therapy in six patients. The presence of DPOAEs may be a useful prognostic factor that positively correlates with recovery from SHL.

Persistent dizziness following head trauma and perilymphatic fistula

A growing body of evidence supports the idea that dizziness that persists for months and even years can be caused by an unsuspected perilymphatic fistula. Perilymphatic fistulas are abnormal ruptures that allow perilymph to leak out of the inner ear into the middle ear space. Most commonly, these ruptures occur secondary to a traumatic event. The term postconcussive syndrome has been used to describe a myriad of symptoms following head trauma. Some of these symptoms, such as cognitive changes, tinnitus, neck stiffness, and dizziness, are also commonly caused by active perilymphatic fistulas. This article discusses the typical history and diagnostic tests for patients with perilymphatic fistula. Common diagnostic tests include audiograms, electronystagmograms, electrocochleograms, and subjective and platform fistula tests. Also, the surgical treatment for the perilymphatic fistula (ie, repair of the oval and round windows) is reviewed, along with the results produced by this relatively minor ear operation. Suggestions are made to help the medical professionals involved in rehabilitative care to be aware of perilymphatic fistulas and seek proper consultations from inner ear specialists if they suspect the existence of this easily cured disorder.

Clinical application of otoacoustic emissions: what do we know about factors influencing measurement and analysis?

Three electrophysiologic audiologic procedures-aural immittance measurement, auditory brainstem response (ABR), and otoacoustic emissions (OAE)- were first described in the 1970's. Immittance measurement and ABR have contributed importantly for years to the assessment of auditory function in children and adults, whereas OAEs have not yet been incorporated into the everyday audiology test battery. In this article, we argue that the transition from OAE measurement by hearing scientists in laboratory settings to routine application by audiologists in the clinic will be greatly facilitated by (1) comprehensive, large-scale studies of the effects of subject characteristics, such as gender and age (from infancy to advancing adulthood), on both transient evoked (TEOAE) and distortion product (DPOAE) otoacoustic emissions; (2) clinical investigations of TEOAE and DPOAE in sizeable patient populations with specific neurotologic diagnoses; (3) guidelines for OAE test protocols in clinical environments; and (4) clear criteria for OAE analysis in clinical populations.

Use of TEOAE, ABR, and Acoustic Reflex Measures to Assess Auditory Function Patients With Acoustic Neuroma

Cochlear and neural auditory function for a series of 30 patients with acoustic neuroma was assessed pre- and postoperatively by transiently evoked otoacoustic emission (TEOAE), auditory brain stem response (ABR), and acoustic reflex measures. Employing a retrosigmoid surgical approach, physical integrity of the acoustic nerve was preserved for 22 patients. TEOAEs were observed preoperatively for 13 patients and postoperatively for 6 of them. Postoperative neural function remained unchanged or improved following surgery for 7 patients, and cochlear function decreased. TEOAE, ABR, and acoustic reflex measurements were considered valuable in providing information about site of lesion and probable mechanisms of injury associated with tumor removal.