Auditory Steady State Response Findings in Adults with Auditory Neuropathy/Dys-synchrony

Auditory steady state response(ASSR) is an auditory evoked response that has received a lot of attention nowadays. At present, ASSR is mostly used to estimate pure-tone thresholds. Clinical evidence of ASSR in combination with findings for auditory middle latency response (AMLR) and 40 Hz response support the assumption that based on stimulus modulation rate, the ASSR anatomic generators are sub-cortical and/or cortical. The goal of the present study was to investigate ASSR findings in a group of young adults with auditory neuropathy/dys-synchrony(AN/AD). Patients and This cross-sectional analytical study was performed on 16 adults with AN/AD (mean age: 20 5.30 years) and 28 subjects with normal hearing(mean age: 22 3.80 years). ASSR test with high rate modulated stimulus was done at four octave frequencies of 500, 1000, 2000 and 4000 Hz on each ear individually in both AN/AD and control groups. Independent t-test was used to compare hearing thresholds obtained by behavioral evaluation and ASSR recording in each studied group individually. Average pure-tone thresholds revealed moderate hearing loss in AN/AD individuals with focus on low frequencies so that the low-tone loss seen in audiograms was observed in almost two-thirds of the subjects, a finding which is common in adults with AN/AD. However, ASSR revealed profound hearing loss at four studied frequencies in all AN/AD patients regardless of behavioral hearing thresholds, and a significant difference was shown between hearing thresholds gained by these two methods, namely PTA and ASSR. Although in clinical setting ASSR is usually used to estimate hearing thresholds in different populations and degrees of hearing loss, its findings are different in AN/AD patients and can be used for differential diagnosis of this disorder. Using high rate modulated stimulus, severe and profound hearing loss or no ASSR is expected in AN/AD. Considering the fact that ABR also leads to the same abnormal results in AN/AD, it seems that the brain generators of both ABR and ASSR are the same and the concordance between their findings can confirm a defect in auditory brainstem function in patients with suspected AN/AD.