[Retrocochlear hearing disorders]

The diagnosis of retrocochlear hearing impairment is mainly based on threshold tone decay, absence of the stapedius reflex, abnormal dichotic speech discrimination and ERA findings. A relatively poor discrimination for monosyllables with regressive understanding at high intensities can also indicate a neural or central lesion provided that the unaffected side has been correctly masked. ERA results mainly show a synchronisation disorder within the brain-stem, i.e. the J V-response is prolonged or cannot be recorded at all. The cortical response N1, however, corresponds to the subjective threshold except that in impairments of the cortex, the N1-response is worse than expected from the pure tone threshold. Representative examples are given.