Distortion-product otoacoustic emission input-output characteristics of misophonic ears with normal hearing

The study aimed to evaluate the cochlear non-linear mechanisms in individuals with misophonia. We compared the absolute amplitude of distortion product otoacoustic emission (DPOAE) as a function of input using distortion product otoacoustic emissions input-output (DPOAE I/O) test and the slope of input-output curve in individuals with and without misophonia.

Total of 60 participants with normal hearing were split into two groups - with misophonia (30 participants, 60 ears) and without misophonia (30 participants, 60 ears), were considered in the study. The misophonic group was further divided into mild (16 participants, 32 ears) and moderate/severe (14 participants, 28 ears) misophonia groups based on the misophonia severity, which was assessed using the misophonia assessment questionnaire (MAQ). DPOAE amplitudes (output) corresponding to input levels of 45 to 75 dB SPL (5 dB steps) were obtained bilaterally for all the participants for six frequencies: 1 kHz, 1.5 kHz, 2 kHz, 3 kHz, 4 kHz, and 6 kHz. Along with amplitude (DPOAE O/P), the DPOAE I/O slope for each of the six frequencies was calculated.

The results of Kruskal Wallis H-test comparing DPOAE amplitudes at different input intensities between the three groups showed a statistically significant difference (p < 0.01) at 2 kHz at all input intensities. Post hoc analysis showed Statistically significant differences (p < 0.05) between (i) non-misophonics and moderate/severe misophonics at all input levels, and (ii) between mild misophonics and moderate/severe misophonics at input levels of 60, 65, 70, and 75 dB SPL. Statistically significant difference was also observed at 1 kHz for input levels of 50, 60, and 75 dB SPL, while post hoc analysis showed no significant differences between the three groups. Individuals with moderate/severe misophonia showed reduced DPOAE amplitudes at all input intensities. Although not statistically significant, the DPOAE I/O mean amplitudes at 1 kHz and 1.5 kHz were lower in individuals with moderate/severe misophonia when compared to individuals without misophonia. The Kruskal Wallis H-test showed no statistically significant difference (p > 0.05) in input-output slope between individuals with (mild or moderate/severe) misophonia and without misophonia.

The results suggest subtle differences in cochlear non-linear mechanisms in individuals with misophonia. These alterations represented at the higher auditory centres may indicate a possible contribution towards misophonia development.