Tympanic electrocochleography for evaluation of endolymphatic hydrops

Abstract

There has been increased interest in electrocochleography for the diagnosis and intraoperative monitoring of patients with endolymphatic hydrops. Attention has been focused on the determination of the summating potential:action potential (SP:AP) ratio from alternating polarity clicks. Review of this technique at the University of Minnesota led to a reevaluation of the usual interpretation of these recordings. Separate examination of the rarefaction and condensation click recordings provides insight into abnormal response patterns. Cases are presented to illustrate a variety of normal and abnormal patterns including abnormal differences in the latency of condensation and rarefaction-click-generated action potentials, increased summating potential, uncanceled cochlear microphonic, and reduced action potential and summating potential amplitudes. These response categories may be useful in understanding the pathophysiology of Meniere's disease.

Cochlear Potentials in Clinical Audiology

“…The TM elec trode is usually a version of a foam tip elec trode [13][14][15] or a chlorided silver wirerayon wick [9,[16][17][18]. A more detailed ac count of TM electrodes is available in a recent review [15] and will not be dealt with here.…”

Electrocochleography Potentials Evoked by Condensation and Rarefaction Clicks Independently Derived by a New Numerical Filtering Approach

“…In particular, in Levine et al [1992] and Johansson et al [1997] systematic differences between the N 1 latencies in the rarefaction and condensation click cases were pointed out, ranging from 0.1 ms in the normal up to 0.70 ms in the pathologic subjects. The diversity of cochlear potentials evoked by clicks of opposite polarity may constitute a valuable indicator in the differential diagnosis of cochlear pathologies Orchik et al, 1998;Sass et al, 1998].…”

“…the difficulty in delivering exactly symmetric clicks and the unpredictable role played by the journey from the sound generator to the cochlea on the stimulus phase. More importantly, physiologic theory, mathematical modeling and clinical evidence [Biondi and Grandori, 1976;Levine et al, 1992;Margolis et al, 1992;Hall, 1992], conclude that CAP and CM in response to condensation and rarefaction clicks may be significantly different, especially in the presence of cochlear pathologies (see Johansson et al [1997] for an attempt to quantify the differences between the N 1 latencies obtained under the two stimulation modalities). Indeed, recent contributions suggested that assessing the influence of stimulus polarity on ECochG potentials may be of help in the understanding of abnormal cochlear responses and in the differential diagnosis of hearing disorders [Sass et al, 1998;Orchik et al, 1998].…”

Da eletrococleografia transtimpânica em pacientes com e sem hydrops endolinfático e limiares auditivos iguais ou maiores que 50 decibéis

“…Esta redução se justifica pela falta de sincronia nos disparos dos neurônios formadores do AP 7 e foi observada por outros autores. 8 A eletrococleografia transtimpânica foi o método de exame utilizado nesta pesquisa, por ser consagrada pela literatura como a que permite a obtenção das melhores respostas, com pouca variabilidade intrateste e interteste. 20,21 A escolha da relação SP/AP como principal parâmetro na avaliação dos resultados foi fundamentada na afirmação de Coats que propôs a avaliação desta relação para diminuir a grande variabilidade interindividual das amplitudes de SP e AP 22 .…”

“…Nas fases avançadas do hydrops endolinfático é comum encontrarmos pacientes com limiares auditivos maiores que 50 decibéis. Estes limiares levam a uma diminuição do AP por destruição das células ciliadas e alteram a relação SP/AP, similarmente ao que ocorre nos tumores no nervo vestibular e nas doenças degenerativas, quando há diminuição do AP por adaptação 7,8 .…”