Discrepancies in Hearing Thresholds between Pure-Tone Audiometry and Auditory Steady-State Response in Non-Malingerers

Objectives: To evaluate discrepancies between pure-tone audiometry (PTA) and auditory steady state response (ASSR) tests in non-malingerers and investigate brain lesions that may explain the discrepancies, especially in cases where the PTA threshold was worse than the estimated ASSR threshold. Design: PTA, speech audiometry, auditory brainstem response, ASSR, and neuroimaging tests were carried out on individuals selected from 995 cases of hearing impairment. Among these, medical records of 25 subjects (19 males, 6 females; mean age = 46.5 +/- 16.0 years) with significant discrepancy between PTA and estimated ASSR thresholds were analyzed retrospectively. To define acceptable levels of discrepancy in PTA and ASSR hearing thresholds, 56 patients (27 males, 29 females; mean age = 53.0 +/- 13.6 years) were selected for the control group. Magnetic resonance images, magnetic resonance angiograms, and positron emission tomograms were reviewed to identify any neurologic abnormalities. Results: Pathologic brain lesions were found in 20 cases (80%) in the study group, all of which showed a significant discrepancy in hearing threshold between PTA and ASSR. Temporal lobe lesions were found in 14 cases (70%), frontal lobe lesions in 12 (60%), and thalamic lesions without the frontal or temporal lobe in 2 cases (10%). On repeated PTA and ASSR tests a few months later, the discrepancy between ASSR and behavioral hearing thresholds was reduced or resolved in 6 cases (85.7%). Temporal lobe lesions were found in all 3 cases in which the estimated ASSR threshold worsened with unchanged PTA threshold, and frontal lobe lesions were found in all 3 cases in which the PTA threshold improved but the estimated ASSR threshold was unchanged. No neurological lesions were found in 5 cases (20%) of patients with a discrepancy between ASSR and behavioral hearing thresholds. Conclusions: Clinicians should not rely exclusively on ASSR, especially in cases of central nervous system including temporal, frontal lobe, or thalamus lesions. If no lesions are found in a neuroimaging study of a patient with a discrepancy between PTA thresholds and estimated ASSR thresholds, further functional studies of the brain may be needed. If clinicians encounter patients with a discrepancy between PTA thresholds and estimated ASSR thresholds, an evaluation of brain lesions and repeat audiologic tests are recommended in lieu of relying solely on ASSR.