ABSTRACT
Vestibular evoked myogenic potentials (VEMPs) were measured in 22 unilateral Menière patients with monaural and binaural stimulation with 250 and 500 Hz tone bursts. For all measurement situations significantly lower VEMP amplitudes were on average measured at the affected side compared to the unaffected side. Unilateral Menière patients have, in contrast to normal subjects, asymmetric VEMPs, indicating a permanently affected vestibular (most likely otolith) system at the side of hearing loss. The diagnostic value of VEMP amplitude asymmetry measurement in individual patients is low, because of the large overlap of the VEMP amplitude asymmetry range for unilateral Menière patients with that for normal subjects.
Subject(s)
Meniere Disease/physiopathology , Vestibular Evoked Myogenic Potentials/physiology , Acoustic Stimulation , Female , Humans , Male , Middle AgedABSTRACT
To investigate the effect on the functioning of the vestibular system of a rupture of Reissner's membrane, artificial endolymph was injected in scala media of ten guinea pigs and vestibular evoked potentials (VsEPs), evoked by vertical acceleration pulses, were measured. Directly after injection of a sufficient volume to cause rupture, all ears showed a complete disappearance of VsEP, followed by partial recovery. To investigate the effect of perilymphatic potassium concentration on the vestibular sensory and neural structures, different concentrations of KCl were injected directly into the vestibule. The KCl injections resulted in a dose-dependent decrease of VsEP, followed by a dose-dependent slow recovery. This animal model clearly shows a disturbing effect of a higher than normal K(+) concentration in perilymph on the vestibular and neural structures in the inner ear. Potassium intoxication is the most probable explanation for the observed effects. It is one of the explanations for Menière attacks.
Subject(s)
Perilymph/chemistry , Potassium/metabolism , Vestibule, Labyrinth/metabolism , Analysis of Variance , Animals , Dose-Response Relationship, Drug , Guinea Pigs , Injections , Meniere Disease/etiology , Meniere Disease/metabolism , Potassium/administration & dosage , Potassium/toxicity , Vestibular Evoked Myogenic PotentialsABSTRACT
To investigate the effect of an acute endolymphatic hydrops on the functioning of the vestibular system a hydrops was created by microinjection of artificial endolymph through the basilar membrane into scala media in 10 guinea pigs. To control for the effect of perforation of the basilar membrane, the same procedure was performed in 9 other guinea pigs, but without injection of endolymph. Contralateral ears served as control ears. Vestibular evoked potentials, evoked by vertical acceleration pulses applied to the guinea pig's head, were measured in all ears before, immediately after, and 2, 4, and 5 hours after perforation/injection. Acute endolymphatic hydrops did not affect the amplitude of the VsEP immediately after injection. After 4 to 5 hours VsEP was significantly reduced in both hydrops and perforated-only ears, compared to control ears. However, no significant difference was found between VsEP of the hydrops ears and perforated-only ears. Reduction of VsEP is not caused by a direct hydromechanical effect on the vestibular system, but possibly by leakage of perilymph through the perforation hole, supporting the membrane rupture theory for Menière-attacks.
Subject(s)
Endolymphatic Hydrops/physiopathology , Evoked Potentials , Vestibule, Labyrinth/physiopathology , Acceleration , Acute Disease , Animals , Basilar Membrane , Cochlear Duct , Endolymph , Endolymphatic Hydrops/etiology , Guinea Pigs , Microinjections , Physical Stimulation/methods , Time FactorsABSTRACT
UNLABELLED: Since 1938 endolymphatic hydrops has generally been accepted as the basic histopathological substrate of Menière's disease. In animal studies it has been found that exogenous administration of aldosterone resulted in endolymphatic hydrops. Manifestations of Menière's disease are frequently observed in times of emotional stress. Mediated through the hypothalamus, stress leads to an increased secretion of adrenocorticotropic hormone from the anterior pituitary gland, followed by an increased adrenocortical production of glucocorticoids (cortisol and corticosterone) and mineralocorticoids (aldosterone). We addressed the question whether plasma aldosterone levels, like in guinea pigs, would be increased in patients with Menière's disease. As part of a diagnostic protocol a clinical prospective cohort study was therefore performed on 89 patients with Menière's disease to assess plasma aldosterone levels. Plasma aldosterone was not elevated in Menière patients compared to plasma aldosterone in a control group of 27 normal subjects. No statistically significant differences were found in plasma aldosterone between uni- and bilateral Menière's disease. Plasma aldosterone levels did not correlate with age, average hearing loss, duration or perceived severity of subjective complaints (vertigo, hearing loss, tinnitus and aural pressure). In this study plasma aldosterone was not elevated in patients with Menière's disease compared to normal subjects. Plasma aldosterone can thus not be used as a diagnostic tool for Menière's disease. IN CONCLUSION: No anomalous plasma aldosterone levels were found in Menière patients during an attack-free period. The question whether plasma aldosterone and cortisol levels show variations before, during and after an attack remains to be answered. If so, this might contribute to a better understanding of the pathophysiological mechanism of Menière's disease.
