Clinical Electrocochleography in Menière´s disease
Sammanfattning: Electrocochleography (ECoG) is an objective method to evaluate cochlear electrophysiology. The recordings are considered to reflect the mechano-electric processes of the cochlea, and can indicate the presence of suspected endolymphatic hydrops. The aim of the present thesis was to investigate the value of transtympanic (TT) ECoG in the clinical diagnosis and management of Menière´s disease. The transtympanic approach offers an optimal signal-to-noise relation, and therefore TT ECoG was used in the studies. A standardized, clinically feasible TT ECoG set-up was presented. It was found that the TT ECoG technique produced reproducible responses in a clinical setting. Patients with Menière´s disease showed significantly larger click evoked summating potential/action potential (SP/AP) ratios and low-frequency burst evoked SP amplitudes, as compared to normal-hearing subjects and patients with other cochlear hearing impairments. Upper limits for the TT ECoG variables, indicating pathology, were calculated. Also upper limits indicating a significant inter-test change in the variables were determined. Using logistic regression it was found that the click evoked SP/AP ratio and the 1 kHz SP amplitude were the variables which most effectively distinguished patients with Menière´s disease from those with other cochlear impairments. It was found that the sensitivity of TT ECoG was 82%, whereas specificity was 95%. Patients with Menière´s disease showed significantly larger differences in AP latencies in response to clicks of opposite polarity, as compared to normal-hearing subjects and patients with other cochlear hearing impairments. The findings of the increased AP latency differences in Menière´s disease, support the theory that TT ECoG reflects the cochlear mechano-electric changes, caused by endolymphatic hydrops. Inclusion of measurements of AP latency differences increased the sensitivity of TT ECoG to 87%. Applications of TT ECoG in clinical practice concerning Menière´s disease were described. Thus, TT ECoG in connection with raised intrathoracic pressure was indicated as a possible method to distinguish patients with Menière´s disease from those with a long-standing perilymphatic fistula. TT ECoG evaluation of short term middle ear pressure treatment in patients with Menière´s disease was conducted. Significant changes in the TT ECoG variables indicated a decrease in endolymphatic hydrops.
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