The clinical value of auditory steady state responses in the audiological assessment of pseudohypacusic workers with noise-induced hearing loss in the South African mining industry

Abstract

Large numbers of South African mine workers incur noise-induced hearing loss. The prevalence of noise-induced hearing loss is such that its financial implications for the industry are significant. This situation is often further compounded by an exaggeration of their hearing loss by some workers in an attempt to obtain compensation. Questionable cases must be re-assessed, increasing the cost of evaluations and the number of unproductive shifts. The inability to obtain true pure-tone thresholds in unco-operative workers leads to ineffectiveness in and frustration for audiologists and occupational health centres because they are not delivering an accountable service to the mining company and individual workers. The failure to obtain pure-tone thresholds may also lead to deserving workers not receiving compensation, and sudden hearing loss not being diagnosed. Workers unfit for their present occupations can also be further exposed to noise. Current audiological procedures can identify instances of exaggerated hearing loss (pseudohypacusis), but do not quantify the extent of exaggeration. Traditional testing techniques require patient co-operation and, hence, are insufficient to resolve cases where patient co-operation is not forthcoming. As a result this study was undertaken to determine the value of auditory steady state responses (ASSRs) as a means of estimating the pure-tone thresholds of noise-exposed workers. ASSRs need no response from the patient, and the electrical responses to the presented sound are measured by means of a real-time statistical analysis of the samples, using a computer, thereby offering real objectivity. The following research question was addressed: “What is the clinical value of ASSRs in the audiological assessment of pseudohypacusic workers with noise-induced hearing loss?” An experimental study was conducted, where different protocols and types of equipment used in the testing of ASSRs were evaluated in a group of min workers with noise-induced hearing loss (n=81). The influence of sedation on the threshold estimation was also evaluated. The proven best protocol was finally evaluated in a pseudohypacusic group of workers (n=29). The study indicates that ASSRs are a valid and accurate alternative to pure-tone testing in populations with noise-induced hearing loss. The test can serve as a once-off test procedure for an unco-operative client. The mean threshold estimates of ASSRs never differed more than 10 dB from the mean pure-tone thresholds. The test procedure was accurate throughout the severity range of hearing loss, and age did not influence the reliability of the threshold estimates. Single-frequency techniques were found to be the technique of choice in this population and it is recommended that the 40 Hz response is employed as a modulation frequency. Sedation did not have any effect on the length and the sensitivity of the procedure, and is thus not advocated if co-operation can be obtained. The length of the procedure is estimated at 60 minutes. Finally, this study has contributed to the validation of the technique (previous research was limited). As a result of this study, the implementation of this procedure in mines’ audiological centres is advocated since it has been proven to be of clinical value.