Abstract
Hyperacusis is a frequent auditory disorder where sounds of normal volume are perceived as too loud or even painfully loud. There is a high degree of co-morbidity between hyperacusis and tinnitus, most hyperacusis patients also have tinnitus, but only about 30–40% of tinnitus patients also show symptoms of hyperacusis. In order to elucidate the mechanisms of hyperacusis, detailed measurements of loudness discomfort levels (LDLs) across the hearing range would be desirable. However, previous studies have only reported LDLs for a restricted frequency range, e.g., from 0.5 to 4 kHz or from 1 to 8 kHz. We have measured audiograms and LDLs in 381 patients with a primary complaint of hyperacusis for the full standard audiometric frequency range from 0.125 to 8 kHz. On average, patients had mild high-frequency hearing loss, but more than a third of the tested ears had normal hearing thresholds (HTs), i.e., ≤20 dB HL. LDLs were found to be significantly decreased compared to a normal-hearing reference group, with average values around 85 dB HL across the frequency range. However, receiver operating characteristic analysis showed that LDL measurements are neither sensitive nor specific enough to serve as a single test for hyperacusis. There was a moderate positive correlation between HTs and LDLs (r = 0.36), i.e., LDLs tended to be higher at frequencies where hearing loss was present, suggesting that hyperacusis is unlikely to be caused by HT increase, in contrast to tinnitus for which hearing loss is a main trigger. Moreover, our finding that LDLs are decreased across the full range of audiometric frequencies, regardless of the pattern or degree of hearing loss, indicates that hyperacusis might be due to a generalized increase in auditory gain. Tinnitus on the other hand is thought to be caused by neuroplastic changes in a restricted frequency range, suggesting that tinnitus and hyperacusis might not share a common mechanism.
Highlights
Hyperacusis is an auditory disorder that is characterized by an “unusual tolerance for everyday sounds” [1], an “abnormal reduced tolerance to environmental sound” [2], or “abnormal increased sound-induced activity within the auditory pathways” [3]
We have found that on average the loudness discomfort levels (LDLs) are almost flat across frequencies from 125 to 8 kHz, and decreased by about 16–18 dB compared to a reference group [12], indicating a certain generalized, frequency-independent distortion of auditory processing or loudness evaluation
LDL values might not always adequately reflect subjective perception in hyperacusis, since all patients sought treatment for problems with sound sensitivity. This might be because we measured LDLs using pure-tone stimuli, and the response to pure tones might reflect perception of real-world sounds only to a certain degree
Summary
Hyperacusis is an auditory disorder that is characterized by an “unusual tolerance for everyday sounds” [1], an “abnormal reduced tolerance to environmental sound” [2], or “abnormal increased sound-induced activity within the auditory pathways” [3]. Many patients describe that everyday sounds, i.e., sounds that would generally be considered to be of normal loudness and comfortable to listen to, are too loud or unbearably loud, causing them discomfort or even pain. Other forms of decreased sound tolerance are misophonia (strong dislike of sounds) or phonophobia (fear of sounds), where specific sounds cause aversive reactions regardless of sound intensity [3]. On Audiometric characteristics of hyperacusis patients the other hand, problems are generally related to sound intensity, and not restricted to specific types of sounds [3, 4]. Even the most conservative estimate of 2% indicates that this is a quite frequent disorder that affects millions
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