Isolated hyperacusis (hypersensitivity to sound) is a relatively uncommon but potentially disabling condition.
It is important to know that hyperacusis does not mean any increased ability or 'better' hearing than in other people. In fact, there is often at the same time some hearing loss at particular frequencies together with discomfort.
Main forms of hyperacusis
There are three main forms of hyperacusis: general hyperacusis, hyperacute hearing and so-called 'misophonia' or soft sound sensitivity.
General hyperacusis is defined as a universal potential to experience uncomfortable oversensitivity of hearing. If the sound sensitivity affects only certain frequencies then it is usually referred to as hyperacute hearing. Again, this is often accompanied by hearing loss at other frequencies.
Misophonia or soft sound sensitivity means the patient is sensitive to specific sounds or noises, which are not necessarily particularly loud.
However, they create a strong emotional response, so that, for example, the sound of someone chewing, or the noise of the scratching of chalk on a board is perceived as highly offensive or upsetting.
The term hyperacusis is often taken to mean the same as 'phonophobia'.
However, the latter also describes the emotional component of the condition, which can create anxious anticipation of uncomfortable hearing that might be triggered independently of loudness or volume. There can be significant reactive psychosomatic features with extensive physical and mental exhaustion.
A frequent source of misunderstanding of hyperacusis is relating it to the recruitment phenomenon. This is an exaggerated response to sound only once a threshold is reached - the typical effect when you raise your voice while trying to talk to deaf people, until they suddenly ask you not to shout at them.
Recruitment is part of the ageing process and usually happens when the upper frequencies of hearing are affected by deafness. Therefore, in these cases, it is often worth trying to speak deeper rather than louder to reach the frequencies that can be received by still intact hearing cells.
Hyperacusis and recruitment are not related. The significant difference between the two is explained physiologically: recruitment is a problem of the peripheral auditory system, meaning the ear and the hair cells, whereas hyperacusis is a problem of the central auditory system.
This means that hyperacusis is more likely to be a partially learned response to a stimulus - which could also explain the frequent emotional component.
Causes of hypersensitivity
The precise mechanism for the development of hyperacusis is often unknown.
It might be unilateral or in both ears, and it can affect a patient gradually or suddenly. A significant proportion of patients notice it after head injuries, after infections, for example of the middle ear, or after ENT surgery. Also, acute acoustic trauma or chronic exposure to noise during work or leisure activities may contribute to, or even cause, the problem.
Apart from this, there is a possible link to migraine and emotional-psychiatric conditions.
Hyperacusis is much more common when there are already features of a hearing problem, predominantly a history of pre-existing tinnitus.
Because it is difficult to recognise and acknowledge the full impact of this invisible problem, it can be difficult for a healthcare professional to engage fully with it and offer straightforward practical help.
Many patients with hyperacusis in any form are convinced that the inner ear is 'damaged' and are tempted to start wearing ear protection to reduce the exposure to noise or specific sounds. It has been found that this worsens the problem, because it increases anxiety and the fixation with sounds.
It is not clear how many people are affected by hyperacusis. Patients with the condition may not experience severe enough disruption of their normal life to ask for help.
Hyperacusis seems to affect mostly adults, with an increase in incidence after the age of 40 years. However, children with autism often seem to be oversensitive to certain sounds.
If the symptoms affect sleep, the resultant feeling of continuous tiredness may worsen the condition and reduce the patient's ability to apply coping mechanisms.
To prevent the patient feeling frustrated, anxious, misunderstood or dismissed it can be useful to display a systematic approach to the problem and gather the relevant information. This at least classifies the symptoms correctly and improves communication and management.
It is easy to confuse hyperacusis with similar problems and features that may point towards different diagnoses. Sometimes it can be necessary to rule out mental illness or psychosomatic origins of the problems. The multiple-activity scale for hyperacusis (MASH) can assess the impact on a patient's life.
As with tinnitus, patients with hyperacusis may worry about a severe underlying disease such as, for example, a brain tumour.
There are, unfortunately, a number of questionable internet resources and self-help groups that are quick to blame healthcare professionals for being unhelpful and uninformed.
Sometimes unvalidated devices (such as recordings of 'pink noise') and techniques for unsupervised home use are privately promoted and sold to patients who feel that they have fallen through the net of healthcare.
These can worsen the symptoms and reinforce behaviours of chronic illness.
If there is significant hearing loss with hyperacusis, a hearing aid might be necessary, but it should be one that prevents overamplification.
Approaches such as tinnitus retraining therapy, audiologic tinnitus management, auditory integration therapy and wearable sound generators can improve patients' confidence and increase sound tolerance. However, they should only be applied by experienced and trained healthcare professionals. It can be a challenge to find a centre to refer the patient without too much inconvenience or delay.
In all cases, counselling can be beneficial. It should ideally involve professionals who are experienced in this area.
In general, hyperacusis has better long-term outcomes than tinnitus.
The level of annoyance and stress experienced by the patient can be an important predictor of improvement after treatment. If a structured approach is used, the success rate for relief of symptoms is 50-85 per cent.
Treatment can last from a few weeks to 10 months, including follow-up.
Dr Jacobi is a salaried GP in York.