Hormones and the auditory system: a review of physiology and pathophysiology.

This review explores the potential role of hormones in modulating the auditory function. The review describes four groups of hormones (the hormones of the circadian cycle, reproduction, stress response and the fluid and electrolyte balance), their physiological variations, interactions, as well as the physiological basis for their effect on the auditory system. Possible contribution of hormones to pathophysiology of auditory dysfunctions, including hyperacusis, tinnitus, Menière's disease and pre-menstrual auditory dysfunction, has also been discussed.

Clinical value of tone burst vestibular evoked myogenic potentials at threshold in acute and stable Ménière's disease.

INTRODUCTION: The objectives of this preliminary, prospective, cohort study were to ascertain the characteristics of vestibular evoked myogenic potentials at threshold levels in two groups of Ménière's disease patients - acute and stable - and to identify whether vestibular evoked myogenic potentials can provide any specific, objective information to distinguish acute from stable Ménière's disease. SUBJECTS AND METHODS: The study was based at a tertiary neuro-otology centre. Twenty adult patients who fulfilled the American Academy of Otolaryngology-Head and Neck Surgery criteria for Ménière's disease were divided into two groups: 11 patients with acute Ménière's disease and nine patients with stable Ménière's disease. Eighteen healthy adult volunteers served as controls. All subjects underwent vestibular evoked myogenic potential testing with ipsilateral, short tone burst stimuli at 500 Hz, as well as pure tone audiometry. The patients also underwent caloric testing. RESULTS: Vestibular evoked myogenic potentials were present in all controls, and were present in 65 per cent of patients but absent in 35 per cent. The mean absolute threshold (Tvestibular evoked myogenic potential) +/- standard deviation in normal controls was 116 +/- 7.7 dBSPL; this did not differ statistically from that in patients, nor did it differ between acute and stable Ménière's disease. The p13/n23 latencies at the threshold levels in the normal, acute and stable groups (mean +/- standard deviation) were respectively: 15 +/- 2.2 ms/23.0 +/- 2.5 ms; 15.7 +/- 0.9 ms/23.7 +/- 0.9 ms; and 15.3 +/- 2.0 ms/24.2 +/- 1.9 ms. The mean interaural amplitude difference ratio (IAD) +/- standard deviation was significantly higher in the stable group compared with the acute group (0.54 +/- 0.33 vs -0.15 +/- 0.22; p = 0.007) and with the controls (0.54 +/- 0.33 vs 0.1 +/- 0.22; p = 0.05). CONCLUSIONS: The parameter that best differentiated acute from stable Ménière's disease at threshold was the interaural amplitude difference ratio. Therefore, this parameter may be used to monitor the clinical course of Ménière's disease.

Progressive auditory neuropathy in patients with Leber's hereditary optic neuropathy.

OBJECTIVE: To investigate auditory neural involvement in patients with Leber's hereditary optic neuropathy (LHON). METHODS: Auditory assessment was undertaken in two patients with LHON. One was a 45 year old woman with Harding disease (multiple-sclerosis-like illness and positive 11778mtDNA mutation) and mild auditory symptoms, whose auditory function was monitored over five years. The other was a 59 year old man with positive 11778mtDNA mutation, who presented with a long standing progressive bilateral hearing loss, moderate on one side and severe to profound on the other. Standard pure tone audiometry, tympanometry, stapedial reflex threshold measurements, stapedial reflex decay, otoacoustic emissions with olivo-cochlear suppression, auditory brain stem responses, and vestibular function tests were undertaken. RESULTS: Both patients had good cochlear function, as judged by otoacoustic emissions (intact outer hair cells) and normal stapedial reflexes (intact inner hair cells). A brain stem lesion was excluded by negative findings on imaging, recordable stapedial reflex thresholds, and, in one of the patients, olivocochlear suppression of otoacoustic emissions. The deterioration of auditory function implied a progressive course in both cases. Vestibular function was unaffected. CONCLUSIONS: The findings are consistent with auditory neuropathy-a lesion of the cochlear nerve presenting with abnormal auditory brain stem responses and with normal inner hair cells and the cochlear nucleus (lower brain stem). The association of auditory neuropathy, or any other auditory dysfunction, with LHON has not been recognised previously. Further studies are necessary to establish whether this is a consistent finding.

Objective evidence for tinnitus from spontaneous emission variability.

Noise exposure is the most common cause for the generation of tinnitus. This study evaluated the variability of spontaneous emissions in industrial workers exposed to noise and reporting the presence of tinnitus in comparison with those exposed to noise but without tinnitus. The assumption being that exposure to noise leads to some instability within the cochlea, which alters the spontaneous emission activity. Thus those experiencing tinnitus may show greater variability than those without tinnitus. 198 mill workers in Poland exposed to noise levels between 85-95dBA for a mean of 12+/-6.6 years, 104 of whom had reported the presence tinnitus and 94 without tinnitus were evaluated for otoscopy, audiometry and otoacoustic emissions. The tests were repeated between 5-10 days in most subjects to check for variability. There were significant differences in the mean age, pure tone average, transient emissions amplitude and variability between groups with and without tinnitus. There were no significant differences between sessions for these measures in either group. Those with tinnitus had poorer thresholds by an average of around 15dB, and reduced TOAE of around 2.6dB compared with those without tinnitus. There are a number of factors such as age, pure tone thresholds and tinntius, which may be responsible for the reduction in emissions. For the purposes of examining SOAE stability, all SOAE peaks were classed as stable if SOAE frequency in the two sessions remained unchanged and variable if SOAE peaks were present in both sessions but shifted in frequency or present in one sessions and absent in the other. SOAE were present in 73.1% of tinnitus group and in 50% of non-tinnitus group. Of these 92% of the tinnitus group had present and variable SOAE whereas 48.9% of the non-tinnitus group did. Thus the positive predictive value was calculated at 65% for those with variable SOAE having tinnitus and significantly higher at 86% negative predictive value for those with stable SOAE having no tinntus. The likelihood ratio of tinnitus being present given that SOAE are present and variable is 1.87 and is significantly reduced for no tinnitus given that SOAE are present and stable at 0.156. This study has clearly demonstrated that the incidence of spontaneous emissions is higher in noise-exposed workers than previously observed and the stability from week to week is significantly lower in those with subjective tinnitus.

Tinnitus after head injury: evidence from otoacoustic emissions.

OBJECTIVE: Tinnitus may be caused by a lesion or dysfunction at any level of the auditory system. This study explores cochlear mechanics using otoacoustic emissions in patients with tinnitus after head injury, in whom there seems to be evidence to support dysfunction within the CNS. METHODS: The study included 20 patients with tinnitus and other auditory symptoms, such as hyperacusis and difficulty in listening in background noise, after head injury, in the presence of an "intact" auditory periphery (normal or near normal audiometric thresholds). They were compared with 20 normal subjects and 12 subjects with head injury, but without tinnitus, who had similar audiometric thresholds. In all subjects otoacoustic emissions, including transient click-evoked (TEOAEs) and spontaneous otoacoustic emissions (SOAEs), were recorded, and a test of efferent medial olivocochlear suppression, consisting of recording of TEOAEs under contralateral stimulation, was performed. RESULTS: A significantly higher prevalence of SOAEs (100%), higher TEOAE response amplitudes, and reduced medial olivocochlear suppression in patients with tinnitus in comparison with subjects without tinnitus have been found. CONCLUSION: These findings have been interpreted to be an extracochlear phenomenon, in which the reduction in central efferent suppression of cochlear mechanics, leading to an increase in cochlear amplifier gain, was subsequent to head injury. Auditory symptoms in these patients seemed to constitute the "disinhibition syndrome".

Presence of tinnitus indicated by variable spontaneous otoacoustic emissions.

Spontaneous otoacoustic emissions (SOAE) have been widely studied in normal subjects, and there is evidence of their high frequency stability in repeated recordings. A study to determine the frequency stability of SOAE in 53 of 100 consecutive patients, who presented with tinnitus and in whom SOAE were recordable, was undertaken. Patients were divided into five aetiologically homogeneous subgroups: (i) those with normal hearing and no identified pathology, (ii) those with sensorineural hearing loss of unknown origin, (iii) those with normal hearing, but complaining of tinnitus related to head injury, (iv) those with endolymphatic hydrops, and (v) those with noise exposure. The control group consisted of 20 subjects, selected on the basis of recordable SOAE from 38 volunteers with normal hearing and no tinnitus. The prevalence of SOAE and their inter-session frequency stability (reproducibility and relative frequency shift) were analysed. In contrast to the controls, the tinnitus group had significantly increased frequency variability of SOAE (lower reproducibility and increased relative frequency shift). The prevalence of subjects with SOAE was not notably different between the controls and subjects with tinnitus, if the tinnitus group was considered in toto, but a striking 100% prevalence of bilaterally present SOAE was observed in the tinnitus subgroup with head injury.

Paroxysmal tinnitus due to a meningioma in the cerebellopontine angle.

A 44 year old woman presented with frequent paroxysms of unilateral tinnitus and ataxia which were abolished by treatment with carbamazepine. Hearing was normal and initially there were no other symptoms or signs between paroxysms. Brain stem evoked responses from the affected left ear were absent and MRI showed a large tumour in the left cerebellopontine angle. This was completely removed and histologically proved to be a meningioma. There were striking similarities to trigeminal neuralgia and other paroxysmal brain stem symptoms which occasionally occur in multiple sclerosis and diseases of the cerebellopontine angle. Possible mechanisms are discussed.