Hyperacusis, for a long time a clinical enigma, can represent a serious challenge for both the professional and the patient, since it is still an under-investigated area. In this article we review what is known about the causes of hyperacusis according to an article in the National Library of Medicine, where a table is presented on the causes investigated so far that we will capture in this article.

In the vast majority of cases the common cause is acoustic trauma.

Conditions in which hyperacusis has been reported as a symptom have been reviewed by Katzenell and Segal, and those identified are listed in the table below. It should be noted, however, that of the peripheral conditions identified, several involve facial nerve dysfunction. Since the facial nerve innervates the stapedial reflex, which is a mechanism for reducing the perceived intensity of impulsive sound, these conditions can reduce the effectiveness of that reflex and thus increase the perceived intensity of the sound.

Table 1- Investigated Causes of Hyperacusis

What about the core conditions? Lyme disease is a systemic infection with the tick-borne spirochete Borrelia burgdorferi that targets specific organs in the body, including the peripheral and central nervous systems. Some caution should be exercised in interpreting reports of hyperacusis because facial palsy may be a feature and thus stapedial reflex dysfunction as described above. However, there are reports of hyperacusis in Lyme disease without facial nerve dysfunction.

Williams syndrome is a disorder characterized by deficits in conceptual reasoning, problem solving, motor control, arithmetic ability, and spatial cognition, with an incidence of 1 in 20,000 live births. Up to 90% of people with this syndrome report hyperacusis, and one proposed mechanism is 5-hydroxytryptamine (5-HT) dysfunction;

Other conditions in which hyperacusis has been reported are midbrain aneurysm and migrainous cerebral infarction. A number of cases of hyperacusis have been reported in multiple sclerosis, although the association is unusual.

Although most cases of hyperacusis are non-syndromic, that is, they do not reflect an underlying medical disorder, a medical evaluation is advisable.

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