Hyperacusis is an auditory disorder in which sounds are perceived as louder than they really are and/or the pain threshold is reduced to levels that affect daily life. Everyday sounds such as clinking dishes, children screaming, dog barking, crumpling plastic bags, the sound of small speakers like those of a mobile phone or laptop, vehicle traffic noise, or even the human voice become intolerable.
There is a long list of symptoms that often accompany hyperacusis, with tinnitus being one of the most common. Some of these symptoms include a feeling of blocked ears, sharp ear pain, burning sensations, pain radiating to areas innervated by the trigeminal nerve (cheeks, jaw, teeth, scalp, etc.), tympanic flutter, sound distortion, vertigo, balance disorders or sore throat.
The exact mechanisms that explain hyperacusis are still unknown. The most widespread theory is that hyperacusis is caused by abnormal hyperactivity in the central sound processing in the brain, and that this hyperactivity was triggered by some external stimulus — for example, an acoustic trauma — which somehow caused a structural change in the auditory cortex. In any case, hyperacusis is not a disease in itself but rather a symptom of its underlying cause, just as happens with tinnitus and other related symptoms.
There are several causes that can trigger hyperacusis. The most common one is acoustic trauma, either acute (sudden exposure to very intense sounds above 140 dB) or chronic (long-term exposure to sounds above 85 dB). The population group most affected by hyperacusis is musicians, making up around 35% of those affected.
Other causes that can lead to hyperacusis include temporomandibular disorder, Ménière’s syndrome, Bell’s palsy, fibromyalgia, autism, multiple sclerosis, post-traumatic stress, brain damage, epilepsy, hyperthyroidism, benzodiazepine or antidepressant withdrawal, magnesium deficiency, Lyme disease, Williams syndrome, and many more.
Hyperacusis is very rare, especially in its most severe forms. The lack of knowledge about this disorder in society (including among health professionals), combined with its invisibility, means that those who suffer from it also have to deal with misunderstanding from the people around them — in some cases even from their own family. Unfortunately, some patients are dismissed and their symptoms are attributed solely to psychological issues. Hyperacusis often appears in people with normal or even very good hearing, at least within the frequency range assessed by standard pure-tone audiometry (125 Hz to 8,000 Hz). The rest of the usual tests performed by ear specialists — such as tuning fork tests, speech audiometry, auditory brainstem responses (ABR), tympanometry or MRI — usually show completely normal results. This is perhaps the main reason for the confusion among professionals unfamiliar with hyperacusis, who may end up attributing the patient’s complaints to hypochondria.
The UCL (Uncomfortable Level) is the sound tolerance or discomfort threshold. It is measured in dB and indicates the intensity at which sounds become uncomfortable. The test consists of listening to pure tones at different frequencies (usually between 250 Hz and 4,000 Hz), starting at a very low volume and gradually increasing it until the patient indicates the point where the sound becomes uncomfortable. This is the main diagnostic tool for hyperacusis and must be performed by an experienced audiologist. It is also known as LDL (Loudness Discomfort Level) or ULL (Uncomfortable Loudness Level).
There are four levels of hyperacusis severity, depending on UCL and the extent to which it affects daily life: mild, moderate, severe and very severe. The lower the UCL, the more severe the hyperacusis. In a healthy person, normal UCL values are around 100 dB. In very severe hyperacusis, UCL can drop to 30 dB in extreme cases.
In the middle ear there are two small muscles: the tensor tympani and the stapedius (the smallest muscle in the human body). Their function is to protect the inner ear from loud sounds. Dysfunction of the tensor tympani causes a group of symptoms known as tonic tensor tympani syndrome (TTTS), which accounts for many of the symptoms experienced by people with hyperacusis. It is believed that this dysfunction may be caused by abnormal hyperactivity in central auditory processing. In addition, there is a link between anxiety, negative emotional responses to sound, stress, etc. and abnormal contraction of the tensor tympani. The greater the aversion to sound, the more likely it is to develop one or several TTTS symptoms, and the more severe they will be. The stapedius muscle is more sensitive to sound than the tensor tympani and is more closely linked to abnormally loud perception of sounds. In rarer cases, dysfunction of the stapedius can lead to what is known as stapedius myoclonus.
There are other auditory disorders that also involve reduced sound tolerance but should not be confused with hyperacusis. These include misophonia, phonophobia and recruitment.
Misophonia and phonophobia are two forms of sound intolerance of psychological and/or neurological origin in which, according to Jastreboff/Hazell, the limbic system and the autonomic nervous system are involved. Misophonia is characterised by a negative emotional reaction to sound. People with misophonia feel anxiety, anger, rage or fear when hearing certain sounds. Phonophobia is a form of misophonia in which fear of sound is experienced in an exaggerated way.
Given the great difficulties involved in living with hyperacusis, it is very common for people who suffer from it to develop, to a greater or lesser extent, misophonia and/or phonophobia. One problem this may cause is confusing hyperacusis symptoms with those of misophonia or phonophobia. If these conditions go undetected, they won’t be treated properly and may seriously disrupt hyperacusis recovery. Therefore, alongside hyperacusis treatment, it may also be necessary to treat these sound intolerance conditions separately. Misophonia and phonophobia are treated mainly by changing one’s attitude towards the sounds that provoke the associated symptoms, and psychological therapy can be very helpful in this regard. A specific sound therapy protocol can also help to avoid focusing attention on the problematic sounds. Finally, the use of anxiolytics and/or antidepressants may be necessary to keep anxiety under control, which is very important when treating hyperacusis. You can find more information about how to treat these disorders in this article.
Pure recruitment is characterised by a sensorineural hearing loss in the inner ear, with reduced perception of low-intensity sounds and normal perception of high-intensity sounds. However, there is a form of recruitment in which not only the hearing threshold is reduced but also the discomfort threshold. The comfortable dynamic range becomes very narrow, so a person with this form of recruitment may need to ask people to speak louder in order to hear them, and then ask them to speak more quietly because it becomes uncomfortable.
In people who suffer from both hyperacusis and tinnitus, spontaneous short-lived tinnitus spikes (called TST — Transient Spontaneous Tinnitus) sometimes appear, typically lasting around 10 seconds. They can appear in one or both ears and at any frequency. The exact causes are unknown, though it is hypothesised that they may result from a stabilisation process of the outer hair cells. Either way, they should not be given any importance as they do not represent any deterioration of hearing or sound tolerance.
As we have already seen, hyperacusis may appear for a number of reasons. In some cases, once the underlying cause is resolved, hyperacusis may disappear completely. But in other cases — such as hyperacusis caused by acoustic trauma — Western medicine currently has no pharmacological or surgical treatment that can cure it. However, hyperacusis can be treated with sound therapy, which can restore a large part of the normal sound tolerance level, reaching UCLs of 100 dB even in very severe cases. Although it does not provide a complete cure, sound therapy and certain precautions in daily life can allow people to return to a normal life.
There are different variations in how sound therapy is carried out to treat hyperacusis, but most are based on the same idea: progressive exposure in both volume and time using broadband sounds (i.e. sounds that contain a wide spectrum of frequencies). Alongside sound therapy, the use of hearing protection (earplugs or earmuffs) is recommended to protect oneself from intolerable sounds and to allow daily activities to continue. However, people with hyperacusis should avoid overuse of hearing protection, as improper use can make the ears even more sensitive to sound.
The time needed to treat hyperacusis with sound therapy is usually long — from a few months to several years — and depends on many factors: the severity of the hyperacusis, relapses, emotional factors, the patient’s sound environment, etc.
Last updated: 11/09/2018
Bibliography
Tyler R, Pienkowski M, et. al. A Review of Hyperacusis and Future Directions: Part I. Definitions and Manifestations. American Journal of Audiology 2014:23:402-419.
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