What is Hyperacusis?

The lack of consistency in defining hyperacusis is frustrating for researchers and patients alike. The following are the most common definitions for terms related to hyperacusis and decreased sound tolerance.

  • Decreased Sound Tolerance- Present when every day sounds cause a negative reaction. This includes most of the conditions listed below.
  • Hyperacusis- Present when every day sounds are perceived as being uncomfortably loud or cause physical pain. Negative reactions to sound caused by something other than uncomfortable loudness or pain (e.g. fear, distortion, tinnitus, annoyance) is not defined as hyperacusis. Misuse of the term “hyperacusis” is common.
    • There is a push to include a sub-definition of the term “hyperacusis” where pain from sound is the primary complaint. “Pain hyperacusis” (Tyler 2014) or “Noxacusis” (Fuchs 2015) are now more commonly used. While “Loudness Hyperacusis” and “Pain Hyperacusis” generally occur together, there is a portion of hyperacusis patients that present loudness hyperacusis without pain and a portion that present pain hyperacusis without increased loudness sensation.
      • Pain Hyperacusis- Present when sounds trigger pain in the ear below common pain thresholds (120 dB).
      • Loudness Hyperacusis- Present when moderately intense sounds are perceived as being uncomfortably loud.
      • Noxacusis- Hyperacusis with pain.
        • This definition does not preclude other symptoms such as increased loudness sensations.
        • “Noxacusis,” originally coined by researchers studying type-II nerves, is popular in patient forums. This term is often used with the subtext that there are potential peripheral mechanisms for pain from sound.
    • The term hearing sensitivity is discouraged as the meaning is ambiguous and it can inaccurately suggests the ability to detect sounds that others cannot hear.
  • Misophonia- Present when everyday sounds cause a negative emotional reaction. Examples of emotions that can be triggered from sound include annoyance, rage and fear. Other researchers wish to drop usage of the term misophonia and instead split this into fear hyperacusis and annoyance hyperacusis in order to to simplify naming and make the terms easier to interpret by the general public.
  • Phonophobia- Present when everyday sounds cause fear (subset of misophonia). Other researchers wish to call this fear hyperacusis in order to make the term easier to interpret by the general public. For some, this is more directly linked to a fear of re-injury or long-term setback.
  • Vestibular Hyperacusis- Present when everyday sounds induce disordered balance or vertigo. This is commonly referred to as Tullio’s Phenomenon.
  • Reactive Tinnitus- Present when everyday sounds increase tinnitus activity. This is not a term used in research literature but commonly used by tinnitus patients. Winding-up and kindling are terms sometimes used to describe similar effects.
  • Distortion from Sound- Present when everyday sounds become distorted. Can cause a negative reaction to loud sounds.
  • Diplacusis- Generally occurs when one ear has sustained more damage than the other.
    • Diplacusis Dysharmonica- Present when a tone is perceived normally in one ear but at a different pitch in the other ear. This is the most common form of diplacusis.
    • Diplacusis Echoica- Present when the timing of tones is slightly different in each ear. The same sound is repeated as an echo.
    • Diplacusis Binauralis- Present when same sound is perceived differently in each ear. This may be a change in pitch or timing.
    • Diplacusis Monauralis- Present when one ear hears the same tone as two different sounds.
  • Acoustic Shock- Acoustic shock is the alteration of auditory function that results from an adverse response to a sudden, unexpected noise event. Tinnitus, hyperacusis, and tonic tensor tympani syndrome (TTTS) are examples of symptoms that can occur as part of acoustic shock.

What is Loudness Recruitment?

Loudness recruitment is not fundamentally related to decreased sound tolerance or hyperacusis. Loudness recruitment is present when sensorineural hearing loss results in an abnormal growth in loudness perception. With pure recruitment, loudness discomfort levels are normal. Soft sounds are perceived at a reduced intensity while loud sounds are perceived at a normal intensity when compared to those with normal hearing. Loudness recruitment can be thought of as an earplug that gradually disappears as sound gets louder. Loudness recruitment leads to the somewhat paradoxical but common request of people to “speak louder” followed by the complaint to “stop shouting” due to the unexpectedly large change in loudness.

  • Those with recruitment may also develop hyperacusis. Hyperacusis symptoms of those with recruitment are often imprecisely described as recruitment symptoms.
  • Recruitment is expected to be a cochlear phenomenon as it is frequency selective and often occurs unilaterally. As described in Potential Mechanisms, there is debate as to whether hyperacusis shares these traits.

Next: Causes

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Liu C, Glowatzki E, Fuchs P. Unmyelinated type II afferent neurons report cochlear damage. Neuroscience 2015:112(47):14723-14727

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