Comparison of summating potential in Menière's disease between trans- and extratympanic electrocochleography

The summating potential (SP) recorded concurrently with transtympanic (TT) and extratympanic (ET) electrocochleography in Menière ears was compared with respect to polarity and amplitude. There was a difference in SP polarity and amplitude between the two methods. The incidence of the increase in the ratio of -SP amplitude to the amplitude of the auditory nerve action potential (AP) (-SP/AP ratio) at 80 dB nHL as a response to a click was higher with the ET than with the TT method. Most of the ears exhibiting an increased +SP/AP ratio with the TT method showed an increased -SP/AP ratio with the ET method. The incidence of increased SP/AP ratios including -SP/AP and +SP/AP ratios was similar with both methods. A +SP was recorded in 14 of 25 ears upon stimulation with an 8-kHz tone burst with the TT method, whereas no +SP was recorded in 25 ears with the ET method. Tone bursts of 1 and 2 kHz produced a -SP and similar waveforms with both methods. Comparison of -SP amplitude recorded with both methods revealed that the ratio of -SP amplitude with both methods is different across the stimulus frequencies. The present study suggests that the -SP elicited by tone bursts of mid to low frequencies is more stable in the diagnosis of Menière's disease than -SP elicited by a click because of the lesser influence of the electrode location and that the increase in the +SP recorded with the TT method may be of clinical significance in the diagnosis of Menière's disease.