McMahon Catherine M, Patuzzi Robert B, Gibson William P R, Sanli Halit
Speech, Hearing and Language Research Centre, Department Linguistics, Macquarie University, NSW, Australia.
Ear Hear. 2008 Jun;29(3):314-25. doi: 10.1097/AUD.0b013e3181662c2a.
The physiological mechanisms underlying auditory neuropathy (AN) remain unclear and it is likely that the multiple disruptions are classified under the broadly defined term. Cochlear implantation is being more widely used in this population to bypass the suspected site-of-lesion although a number of cases have been identified within the Sydney Cochlear Implant Centre where this management strategy has been unsuccessful. It is likely that this relates to the different physiological mechanisms underlying AN.
To investigate the site-of-lesion in AN, frequency-specific round window electrocochleography (ECochG) was used to assess local hair-cell, dendritic, and axonal currents generated within the cochlea in 14 subjects with AN and compared with responses from two normally hearing subjects. ECochG results were then compared with electrically evoked auditory brain stem response (EABR) measured after cochlear implantation.
The results of this study demonstrate that two dominant patterns of ECochG waveforms (produced by a high-frequency alternating tone burst) can be identified in this population of AN subjects: (a) gross waveform showing a prolonged summating potential (SP) latency that, in most cases, is followed by a small compound action potential; and (b) gross waveform showing a normal latency SP waveform followed by a broad negative potential [assumed to reflect the dendritic potential (DP) identified in anaesthetized guinea-pigs]. This study demonstrates that in most subjects (n = 7) with a prolonged latency SP but no DP, normal morphology EABR waveforms were elicited for all electrode channels. On the other hand, all subjects (n = 7) who showed a normal latency SP followed by a broad negative DP, showed EABR waveforms that were absent or having poor wave V morphology. The authors' interpretation of this is that ECochG results may provide a classification of AN into pre- and postsynaptic lesions.
We suggest that a presynaptic and postsynaptic type of AN exist that may have implications for the fitting of cochlear implants.
听觉神经病（AN）的生理机制仍不清楚，很可能多种功能障碍都可归类于这个广义术语之下。尽管悉尼人工耳蜗植入中心已发现一些病例中这种治疗策略未成功，但人工耳蜗植入在这一人群中应用越来越广泛，以绕过疑似病变部位。这可能与AN潜在的不同生理机制有关。
为研究AN的病变部位，采用频率特异性圆窗电耳蜗图（ECochG）评估14例AN患者耳蜗内产生的局部毛细胞、树突和轴突电流，并与两名听力正常受试者的反应进行比较。然后将ECochG结果与人工耳蜗植入后测量的电诱发听性脑干反应（EABR）进行比较。
本研究结果表明，在这组AN受试者中可识别出两种主要的ECochG波形模式（由高频交替短音诱发）：（a）总体波形显示总和电位（SP）潜伏期延长，在大多数情况下，随后是小的复合动作电位；（b）总体波形显示SP波形潜伏期正常，随后是一个宽的负电位[假定反映在麻醉豚鼠中识别出的树突电位（DP）]。本研究表明，在大多数SP潜伏期延长但无DP的受试者（n = 7）中，所有电极通道均引出了形态正常的EABR波形。另一方面，所有显示SP潜伏期正常随后是宽负DP的受试者（n = 7），其EABR波形缺失或V波形态不佳。作者对此的解释是，ECochG结果可能将AN分为突触前和突触后病变。
我们认为存在突触前和突触后型AN，这可能对人工耳蜗的选配具有重要意义。
