Promontory Stimulation EABR in Sensorineural Hearing Loss

Kim, Lee Suk; Ahn, Young Min; Heo, Seong Duk; Kim, Sang Reyul

Abstract

BACKGROUND AND OBJECTIVES: Cochlear implants help patients who suffer from profound hearing loss and for whom hearing aids do not provide enough beneift rehabilitation. Promontory stimulation test (PST), a part of preoperative evaluation for cochlear implants, is not appropriate for prelingually deafened adults and young children because it is measured by the patient's subjective expression to electrical stimulation. Recently, promontory stimulation EABR (PS-EABR) was studied in order to compensate for this disadvantage of PST. The aim of this study is to investigate the feasibility of PS-EABR in the assessment of neural survival of auditory nerve. MATERIALS AND METHOD: PS-EABRs were recorded from subjects with sensorineural hearing loss (group l; pure tone average-between 40 to 70 dB HL) and deafness (group ll; pure tone average < 90 dB HL). Electrical stimulation was performed with the tip of a transtympanic electrode placed on the promontory near the round window niche. We compared PS-EABR waveforms, thresholds, wave V latencies and amplitudes.
RESULTS
Stable PS-EABR waveforms were obtained in both groups. The typical PS-EABR waveform consisted of a series of two to three peaks. The largest peak among them was the wave V which is was not identifiable due to a stimulus artifact. The mean thresholds of PS-EABR were 389.3 +/- 220.3 microampere in the group l and 921.4 +/- 610.4 microampere in the group ll. The maximal acceptable level (MAL) was 746.4 +/- 371.3 microampere in the group l and 2150 +/- 980.2 microampere in the group ll. The mean wave V latencies at threshold level were 4.63 +/- 0.07 msec in the group l and 4.58 +/- 0.35 msec in the group ll and were not significantly changed as the stimulus intensity increased. There was no statistical significant difference between these two groups. The mean wave V amplitudes at threshold level were 0.65 +/- 0.58 microvoltin the group l and 0.89 +/- 1.04 microvoltin the group ll. The amplitude of the wave V in the group l and the group ll increased as the stimulus intensity increased. There was no significant difference between these two groups.
CONCLUSION
The results of this study suggest that PS-EABR will be useful in preoperative evaluation of neural survival in young children and prelinguistically deafened adults with limited communication abilities.