Frequency characteristics of summating potential in Menière's disease

Apical hair cell degeneration causes the increase in the amplitude of summating potential

CONCLUSION

This study indicates that the lesion of hair cells in the apical turn of the cochlea can cause the change in the summating potential (SP)/Compound potential (CAP) ratio.

OBJECTIVES

Electrocochleography is a valuable clinic test for diagnosis of cochlear pathologies and the ratio of SP to CAP has been used to identify Meniere's disease. However, it remains controversial whether the increase of the SP/CAP ratio represents exclusively the endolymphatic hydrops.

METHOD

This study measured the SP and CAP in mice that displayed outer hair cell (OHC) degeneration in the apical section of the cochlea as their age increased.

RESULTS

As compared with the mice aged 8-10 months, the 24-month old mice displayed a significant increase in the amplitude of SP at 12-16 kHz. This result suggests that the degeneration of OHCs in the apical turn leads to the increase of the + SP at the middle frequencies. In contrast, the aging mice did not have a significant change in the CAP amplitude at super-threshold levels.

Electrocochleographic findings: Menière's disease versus sudden sensorineural hearing loss

Electrocochleography was conducted in 185 patients with Menière's disease and 117 with sudden deafness. Electrophysiological findings from the two groups were compared in order to identify pathogenic similarities between the two conditions. Parameters investigated were the summating potential (SP)/action potential (AP) ratio, audiometric profiles and audiometric changes after medical therapy. A high SP/AP ratio was found in the patients with sudden deafness, thus supporting a possible hydropic aetiology in this group. In conclusion, electrocochleography can be considered a useful technique as it permits identification of an hydropic condition in certain cases of sudden deafness.