[Auditory neuropathy: Findings of behavioral physiological and neurophysiological tests]

ABSTRACT

Auditory neuropathy [AN] can be diagnosed by abnormal auditory brainstem response [ABR], in the presence of normal cochlear microphonic [CM] and otoacoustic emissions [OAEs]. The aim of this study was to investigate the ABR and other electrodiagnostic test results of 6 patients suspicious to AN with problems in speech recognition. This cross sectional study was conducted on 6 AN patients with different ages evaluated by pure tone audiometry, speech discrimination score [SDS], immittance audiometry. ElectroCochleoGraphy, ABR, middle latency response [MLR], Late latency response [LLR], and OAEs. Behavioral pure tone audiometric tests showed moderate to profound hearing loss. SDS was so poor which is not in accordance with pure tone thresholds. All patients had normal tympanogram but absent acoustic reflexes. CMs and OAEs were within normal limits. There was no contra lateral suppression of OAEs. None of cases had normal ABR or MLR although LLR was recorded in 4. All patients in this study are typical cases of auditory neuropathy. Despite having abnormal input, LLR remains normal that indicates differences in auditory evoked potentials related to required neural synchrony. These findings show that auditory cortex may play a role in regulating presentation of deficient signals along auditory pathways in primary steps: