Audiometric Profiles of Children with Autism Spectrum Disorders

Background: Several lines of data indicate that abnormalities in auditory processing contribute to functional deficits in the autism spectrum disorders (ASDs). However, the relative impact of peripheral versus central dysfunction is presently underspecified. Particularly concerning is the possibility that partial hearing loss or other peripheral problems may have a cascade effect leading to a systemic failure in auditory processing, especially since distorted auditory perception may have more pervasive impact on functioning than a failure to hear at all (Klin, 1993).

Objectives: To characterize audiometric profiles in children with ASDs.

Methods: Participants were 28 children (aged 5-16) diagnosed with an ASD. Diagnosis was confirmed through detailed assessment, including the ADI-R, ADOS and clinical history.  Audiological examination included Tympanometry and Pure Tone Audiometry (PTA), along with evaluation of Transiently Evoked Otoacoustic Emissions (TEOAE), the Stapedius Reflex Threshold (SRT), and Uncomfortable Loudness Levels (UCL). 

Results: Rates of missing data due to limited comprehension of task demands or noncompliance with procedures included 3.57% (n=1) for PTA and Tympanometry, 42.86% (n=12) for SRT and UCL, and 7.14% (n=2) for TEOAE. Three participants (11.54%) had abnormal tympanometry measures, with one additional participant demonstrating excessive, although not definitively abnormal, eardrum mobility.  Only one subject showed evidence of significant hearing loss on PTA.  TEOAE was clearly abnormal in 15.38% (n=4) of the 26 participants that could be tested, with three additional subjects showing anomalous emissions for at least one of the tested frequencies. An abnormal SRT was found in 18.75% (n=3) of the 16 participants who could be tested.  Overall, 35.71% of participants (n=10) were rated as abnormal on at least one measure of audiological functioning.  It is also noteworthy that abnormal loudness perception, as defined by uncomfortable loudness levels less than 90dB was identified in 8/18 participants (44.44%) for the right ear, and 7/18 for the left ear (38.89%).  Point-biserial correlations between average bilateral UCL level and measures of peripheral audiology were not significant across PTA, TEOAE, and SRT.

Conclusions: The incidence of an abnormal finding on at least one measure of audiological functioning was higher in children with an ASD than has been reported for the general population (35.71% for the present study versus 14.9% of children aged 6-19 years according to CDC's Third National Health and Nutrition Examination Survey, 1988 – 1994).  The presence of sound sensitivity in at least one ear was also considerably higher for the ASD population (44.44% for ASD versus a general population estimate ranging from 8-15.2%; Baguley, 2003).  Patients with tinnitus and those with William’s syndrome also demonstrate a high prevalence of sound sensitivities. In these conditions, the anomalies in loudness perception are almost always associated with peripheral hearing loss. In contrast, sound sensitivities in children with autism were not significantly associated with peripheral hearing anomalies. This suggests a central origin for sound sensitivities in autism, and it indicates that treatment approaches viable in tinnitus and Williams syndrome may not be applicable in the ASDs.