PP1004 - Audiological Tests Used in the Evaluation of the Effects of Solvents on the Human Auditory System

This review synthesized evidence on audiological evaluation of workers exposed to solvents. Using Covidence, 454 references were assessed for eligibility. Ultimately, 37 studies were selected and examined for results and risk of bias.  Data from 25 different audiological tests were analyzed. The quality for most studies, individually, was moderate; overall, the quality of evidence was considered low. Due to discrepancies between studies, the best test battery to assess the auditory effects of occupational solvents was unclear. However, current evidence identified types of auditory dysfunctions to be expected and important characteristics an audiological test battery for solvent exposed workers should include.

Summary:

Rationale: The measurable effects of workplace chemical exposures, such as toluene, styrene, and xylene, on the auditory system are diverse. Taking into consideration that neurotoxic effects of solvents can impact many different biological pathways and structures important to processing sound in both the ear and the brain, the use of a battery of tests has been proposed. However, there is still no clear consensus about which tests should be included in this battery. Thus, this study aimed to scope the literature, identify knowledge gaps, appraise results, and synthesize the evidence on the audiological evaluation of workers exposed to solvents.

Design: We searched Medline; PubMed; Embase; CINAHL; NIOSHTIC-2 to March 22, 2021. Using Covidence, 2 authors independently assessed study eligibility, risk of bias, and extracted data. National Institute of Health Quality Assessment Tools were used in the quality evaluation of included studies; the Downs and Black checklist was used to assess the risk of bias.

Results: Of 454 located references 37 were included. The 37 papers reviewed demonstrate that a variety of tests have been used to evaluate many aspects of auditory function in workers exposed to solvents. Twenty-five tests were studied: two tests to measure hearing thresholds, one test to measure word recognition in quiet, six electroacoustic procedures, four electrophysiological tests, and twelve behavioral tests used to assess auditory processing skills. In addition, it was also used one self-report questionnaire.  Pure-tone audiometry was the most used auditory test, and Auditory Brainstem Response was the second most used test. Few studies used the Amsterdam Inventory for Auditory Disability and Handicap self-report questionnaire, or assessed auditory processing skills through the Dichotic Digit, Filtered Speech, Hearing-in-Noise, Pitch Pattern Sequence, or Random Gap Detection behavioral tests. All studies which used these six tests reported significant differences among solvent-exposed groups, so we suggest future research and clinical practice focus on these tests. The quality of individual studies was mostly considered moderate, but the overall quality of evidence was considered low.

Conclusions: The discrepancies between studies and differences in the methodologies/outcomes prevent recommending a specific test battery to assess the auditory effects of occupational solvents. Current evidence however allows us to identify the type of auditory dysfunctions to be expected and characteristics that an audiological test battery for solvent exposed workers should have. Furthermore, information provided by the current review should facilitate the development of high-quality studies in the future to better address these existing gaps and limitations. Finally, the absence of conclusive evidence should not be interpreted as evidence of lack of effectiveness for the audiological methodologies studied. Rather, it means that further research in occupational ototoxicity determination is very likely to have an important impact.