Article révisé par les pairs
| Résumé : | This chapter reviews the respective contributions of three categories of evoked responses to the evaluation of Auditory Neuropathy/Auditory Dys-synchrony. 1. Short-latency evoked potentials and Oto-Acoustic Emissions. The definite diagnosis of Auditory Neuropathy/Auditory Dys-synchrony relies on an operational definition which requires the demonstration of profoundly altered Auditory Brainstem Responses including wave I, combined with preserved physiological response of Outer Hair Cells. When Oto-Acoustic Emissions are present the latter condition is easy to document In practice however, emissions are often absent, either because of abnormal middle ear status or because they disappear as disease progresses. This means that in many cases the presence of an isolated Cochlear Microphonic Potential is the only remaining clue to the correct diagnosis. This chapter explains and illustrates the various recording strategies that contribute to a correct detection and identification of the Cochlear Microphonic Potential. These include: a. Systematic comparison of both acoustic polarities of the stimulus. b. Stimulus delivery incorporating an acoustic delay in order to avoid confusion with electromagnetic artifacts radiated by the transducer. c. Checking the pre-synaptic nature of the recorded signal i.e. a fixed latency across intensities, the absence of adaptation to high stimulation rates and persistence in presence of masking noise. 2. Long-Latency cortical Evoked Potentials. Some data suggest that they could, when preserved, be associated with a less severe form of desynchronization and be associated with a favourable response to conventional amplification. 3. Auditory Steady Stats Evoked Potentials. They can be absent, but in most cases are obtained at intensities for which the brainstem potentials are absent, thus adding another type of paradoxical result to the overall picture. However, behavioural thresholds cannot be reliably estimated from neurophysiological ones. |
