Speech-in-noise testing as a marker for noise-induced hearing loss and tinnitus

Noise-induced hearing loss and tinnitus are auditory complaints that often co-occur. Often, there is no immediate indication of changes in the pure tone audiogram. Patients can still have clinically normal hearing thresholds while clearly experiencing reduced speech comprehension. This might be explained by the process of neurodegeneration of the innervated dendrites of the auditory nerve fibres and secondary degeneration of spiral ganglion neurons. Subsequent maladaptive neuronal plasticity of the central auditory system can induce tinnitus. Standard hearing testing is no longer sufficient in these patients. Therefore more complex tasks, such as speech-in-noise tests, might be valuable extensions to the standard hearing tests. We carried out a prospective investigation of the influence of tinnitus upon speech comprehension in noise and the effectiveness of speech-in-noise testing, using the Flemish version of the digit triplet test (DTT). Thirty-seven patients with mild noise induced hearing loss, tinnitus complaints and clinically normal pure tone thresholds completed the DTI' and filled in two tinnitus enquiries. A statistically significant (p=0.026) correlation between the averaged high PTA(1,2,4 kHz) and the averaged SRT across ears on the DTT was found. There also seems to be a slight influence of tinnitus onset on the SRT score.