​Early Latency Auditory Evoked Potentials in Retrocochlear Disease and Auditory Neuropathy Spectrum Disorder

The Auditory Brainstem Response in Retrocochlear Disease

  • Early latency auditory evoked potentials specifically the ABR have been considered a primary functional measure of retrocochlear ear disease for several decades
  • very high sensitivity of ABR to tumors of the eighth cranial nerve
  • many clinics now bypass ABR testing in favor of imaging techniques in patients suspected of having retrocochlear involvement

Candidacy for Neurodiagnostic ABR Testing

  • Unilateral tinnitus, unilateral or asymmetric sensorineural hearing loss, unexplained dizziness, facial nerve symptoms, significant hearing loss with normal otoacoustic emissions, unexplained poor word recognition scores or speech in noise scores, head injury and the onset of auditory processing disorders

Recommended Stimulus and Recording Parameters

  • Stimulus type: 100 usec click
    • the extreme brevity of the click stimulus onset will cause a highly synchronous firing of neurons innervating the basal regions of the cochlea and the broadband nature of the stimulus will maximize the number of neurons that evoke the response
    • for patients with severe high frequency loss or an extreme high frequency asymmetry, the ABR can be evoked using tone burss centered at a frequency at which hearing is more symmetric then compared with the wave V interaural latency difference ILD V
  • Rate: 21/s
  • Intensity: 80 db nHL or greater
  • Masking: contralateral wideband noise
  • Polarity: Alternating with the ability to view separate rarefaction and condensation clicks

Determining a Normal or Abnormal Neurodiagnostic ABR

  • the two most powerful ABR indices are the wave I-V interpeak latency and the interaural latency difference of wave V

Auditory Neuropathy Spectrum Disorder

  • sensorineural hearing loss in that the site of the lesion involves the cochlea and/or the auditory nerve
  • ANSD is defined as present outer hair cell function accompanied by dyssynchronous auditory neural responses
  • Evoked Potential measures are the defining features in the diagnosis of ANSD
    • present otoacoustic emissions and/or cochlear microphonic
    • absent ABR

Cochlear Microphonic and Auditory Brainstem Response

  • electrical current generated by the OHCs as they depolarize and hyperpolarize in response to a stimulus