Determination of a Threshold Adjusted Noise Prescription for Tinnitus Management

Abstract

Background: Tinnitus refers to the perception of auditory sensations in the absence of external stimuli (McFadden, 1982). Sound therapy refers to the use of sound to convey positive effects on tinnitus (Searchfield, Linford & Durai, 2017). Threshold adjusted noise (TAN) aims to equalise audibility of a broadband noise across individual audiometric thresholds (Searchfield, Warr, Kuklinski & Purdy, 2002, Callaway, 2014). Aims: To elucidate the optimal masker level of TAN for acute tinnitus improvement, defined as reductions in tinnitus loudness and annoyance, and determine factors affecting acute effectiveness of TAN in sound therapy. Methods: In a randomised cross-over trial design, 20 tinnitus participants (12 males, 8 females) trialled four TAN prescriptions over 10-minute intervals in a sound-treated room. Baseline and outcome measures were visual analogue scale (VAS) scores of tinnitus loudness and annoyance, noise annoyance and sound quality. Results: Results indicated the self-adjusted TAN prescription, set at approximately 72.8% of preferred narrowband listening levels and minimum masking levels, contributed the most acute reductions in tinnitus loudness and annoyance, but also elicited the most noise annoyance. Analysis of variance indicated no significant differences in VAS scores between TAN prescriptions, but VAS scores were significantly different from each other. Bivariate correlation analysis indicated change in tinnitus loudness was strongly positively correlated with change in tinnitus annoyance (r= 0.810, p<0.001), whereas noise annoyance and sound quality were weakly inversely correlated (r = -0.355, p = 0.001). Both correlations were significant. Differences in individual and tinnitus characteristics (age, TFI scores, HADS scores, hearing loss and tinnitus pitch) had no significant effects on the selfadjusted TAN prescription. Conclusions: Optimal partial masking levels to achieve tinnitus reduction varied between individuals, suggestive of an effective range of partial masking levels for use in sound therapy. Separate adaptation levels were suggested to exist for tinnitus and sound audibility. A participant-driven approach for use of TAN in sound therapy is recommended to accommodate heterogeneous tinnitus and individual characteristics. However, the optimal TAN prescription remains to be validated for efficacy in a long-term trial. Suggestions for future research are also recommended.