SPECIAL FEATURE
how they differ, and how they can be diagnosed and treated.2 This article focuses on explaining how loudness hyperacusis differs from pain hyperacusis.
Loudness Hyperacusis Definition Loudness hyperacusis is the experience of uncomfortable-tounbearable physical sensations (exclusive of piercing, burning, or stabbing pain) in the ears and/or head when exposed to any sound at intensity levels that would not be uncomfortable for the typical person.2
Symptoms This definition is the basis for diagnosing loudness hyperacusis. The physical symptoms might involve an uncomfortable sense of fullness in one or both ears (like a balloon being blown up inside the ear), dull earache, or headache. The sensations are often difficult to describe, but they are not
typically characterized using adjectives such as “piercing,” “burning,” or “stabbing” that would indicate severe physical pain. Although loudness hyperacusis can occur in isolation, it is commonly associated with a range of audiovestibular, neurological, psychological, and neurodevelopmental conditions, including tinnitus, hearing loss, migraine, autism spectrum disorder, brain injury, William’s syndrome, and post-traumatic stress disorder, to name a few.3,4
Theorized Mechanisms Loudness hyperacusis is widely believed to be caused by heightened central auditory gain (i.e., the “volume control” in the brain is turned up too high).5–7 “A consensus is emerging in the auditory neuroscience literature that hyperacusis may be associated with a sustained and persistent increase in central auditory gain.”8
“A sound hypersensitivity disorder is characterized by interference with or prevention of participation in normal life activities because everyday sounds cause physical discomfort, pain, negative emotional reactions, fear, or some combination of these symptoms.”
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What is central auditory gain? Briefly, all neurons in the central auditory system fire spontaneously even in the absence of sound, which is normal for everyone.2 The spontaneous activity has a “set point,” which is recalibrated depending on the level of sound entering the ears.5,9 During an extended period of quiet or when there is hearing loss, the set point may be raised such that the central auditory system amplifies sound more than usual, which could result in loudness hyperacusis. Another source of physical discomfort can be caused by tightening of the tensor tympani muscle—one of the two middle-ear muscles that contracts to stiffen the middle-ear bones (ossicles)—which reduces the amount of sound energy entering the cochlea.2 Physical discomfort associated with loudness hyperacusis could be due to everyday sounds causing contraction of the tensor tympani muscle, which would cause fullness in the ear and other uncomfortable sensations, often described as “pain” but not meeting the definition for pain hyperacusis as explained below. Some people have tensor tympani syndrome, which could explain why the tensor tympani contracts so easily with sound exposure.
Treatment Treatment often involves some type of systematic sound exposure to desensitize (or recalibrate) central auditory gain. These interventions typically focus on alleviating the physical discomfort caused by sound. If a patient also has negative emotional reactions to this physical discomfort, then resolving the
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