[Influence of the hearing loss level and auditory sensation curve type on click evoked SP/AP amplitude ratio in Menière's disease]

Abstract

Objective: To assess the influence of hearing loss level and auditory sensation curve type on click evoked SP/AP amplitude ratio (negative summating potential/action potential) in the diagnosis of Meniere's disease.

Method: AP and SP was recorded with tympanic ECochG in normal controls (50 ears), patients with sensorineural hearing loss (SNHL) and patients with Meniere's disease (90 ears) which were further divided based upon the degree of hearing loss and audiometric configuration. SP/AP amplitude ratio was calculated and analyzed.

Result: AP latency in the three groups had no significant differences. AP amplitude in normal hearing subjects was higher than other two patients groups (P < 0.05). Amplitude of SP of control group was higher than that of SNHL group (P < 0.01), but lower than Meniere's disease group (P < 0.01). SP/AP amplitude ratio in Meniere's disease ears was (48.09 +/- 14.83)%, which was significantly higher than that of SNHL group (20.20 +/- 15.00)% (P < 0.01) and normal group (23.85 +/- 8.05)% (P < 0.01). In Meniere's disease ears, SP/AP amplitude ratio was positively correlated to pure tone thresholds (r = 0.5601 P < 0.01). An elevated SP/AP ratio was found in 73% of the Meniere's ears and 6% of the SNHL ears. SP/AP ratio among the different levels of hearing loss in Meniere's disease ears, of the ears with mild hearing loss was lower than those with moderate (P < 0.01) and severe hearing loss (P < 0.01), but between later groups there was no statistical significant difference (P > 0.05). Positive rate of SP/AP ratio was 63% in mild, 83% in moderate, 73% in severe hearing loss ears respectively. SP/AP amplitude ratio in patients with low tone auditory curve type was lower than that with flat type(P < 0.05), the latter had no significant difference (P > 0.05) compared with high tone type. Positive rate was 67.57% in low tone type, 75% in high tone type and 78% in flat tone type respectively.

Conclusion: Results suggests the increase of SP/AP ratio was of clinical significance in the diagnosis of Meniere's disease, and was with advancing pure tone thresholds in certain range of hearing loss levels. Click evoked SP/AP amplitude ratio was affected by degree of hearing loss and auditory sensation curve as well, perhaps the influence of the former on SP/AP ratio was considerable significant.