Decreased sound tolerance includes more than one phenomenon. In the past, we have used two terms: Hyperacusis to describe patients experiencing discomfort to sound resulting from abnormally high activation of the auditory system. Phonophobia was used for patients expressing a fear of certain sounds, or all sounds and resulting from abnormal activation of the limbic and autonomic nervous systems.
Clinical observations reveal that in many cases, decreased sound tolerance consists of more that one problem. It is not necessarily loud sounds, but even quiet sounds, which can cause discomfort. Decreased sound tolerance might reflect a physical discomfort, or can be related to a dislike or a fear of sound.
Hyperacusis can be defined as an abnormally strong reaction to sound occurring within the auditory pathways. At the behavioral level, it is manifested by a patient experiencing physical discomfort as a result of exposure to sound (quiet, medium or loud). The same sound would not evoke a similar reaction in the average listener. The strength of the reaction is controlled by the physical characteristics of the sound, e.g., its spectrum and intensity.
Misophonia and phonophobia can be defined as abnormally strong reactions of the autonomic and limbic systems resulting from enhanced connections between the auditory and limbic systems. Importantly, misophonia and phonophobia do not involve a significant activation of the auditory system. At the behavioral level, patients have a negative attitude to sound (misophonia), or are afraid of sound (phonophobia). In cases of misophonia and phonophobia, the strength of the patient’s reaction is only partially determined by the physical characteristics of the upsetting sound. It is also dependent on the patient’s previous evaluation and recollection of the sound (e.g., sound as a potential threat, and/or the belief that the sound can be harmful), the patient’s psychological profile and the context in which the sound is presented.
Medical conditions previously linked to decreased sound tolerance include: tinnitus, Bell’s palsy, Lyme Disease, Williams Syndrome, Ramsay Hunt Syndrome, stapedectomy, perilymphatic fistula, head injury, migraine, depression, withdrawal from benzodiazepines, increased Cerebral Spinal Fluid (CSF) pressure and Addison’s disease.
Most frequently, significantly decreased sound tolerance results from a combination of hyperacusis and misophonia/phonophobia.
While there is no clearly accepted consensus method for the evaluation of decreased sound tolerance, there appears to be general agreement that loudness discomfort levels (LDLs) provide a reasonable estimation of the problem.
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