Electrocochleography in retrosigmoid vestibular nerve section for intractable vertigo caused by Menière's disease

Interest in electrocochleography has increased in recent years because of the discovery of an elevated summating potential to action potential amplitude ratio (SP/AP ratio) in patients with endolymphatic hydrops caused by Menière's disease or perilymph fistula. It was the purpose of this investigation to determine whether the intraoperative SP/AP ratio will decrease after vestibular nerve section in patients with intractable Meniere's disease. Fourteen patients with medically intractable classic Menière's disease underwent retrosigmoid vestibular nerve section. Intraoperative transtympanic electrocochleography was performed with alternating click stimuli presented at 95 dB HL. In all patients the SP/AP ratio was recorded before the skin incision ("baseline" condition) and after the dura was closed ("closing" condition). Statistical analysis was applied to the recorded data. In 11 (79%) patients, the SP/AP ratio was found to be elevated above 0.30 in the baseline state. In 13 (93%) patients, the SP/AP ratio decreased more than 25% after the nerve was sectioned. These results were highly statistically significant (p < 0.001). We conclude that the SP/AP ratio does decrease in patients with Menière's disease after undergoing retrosigmoid vestibular nerve section and offer a possible explanation.