Acoustic Shock

 What is acoustic shock?

An acoustic shock is an involuntary startle and fright reaction to a sudden, loud, unexpected sound, leading to a typical cluster of involuntary, highly specific symptoms.

Acoustic Shock becomes an acoustic shock disorder or acoustic shock injury if symptoms persist.   Acoustic Shock needs to be distinguished from, and is separate and different to, inner ear damage from noise exposure, also known as acoustic trauma, causing a noise induced hearing loss.

Acoustic Incidents

The acoustic incident resulting in an acoustic shock is always an unexpected or unpredictable sound, triggering a strong startle and threat response.

Additionally, acoustic incidents leading to acoustic shock are often:

  • loud
  • sudden or have an impact quality
  • threatening
  • in close proximity to the ear(s)
  • occurring in a situation where the person is unable to move away from the sound
  • outside the person’s control

Call centre staff wearing a headset are vulnerable to acoustic shock, and the research has tended to focus on this group.

However, acoustic incidents can occur anywhere.

Acoustic incidents through a telephone line can originate as feedback oscillation, fax tones, signalling tones, or even malicious whistleblowing by dissatisfied call centre customers. Acoustic shock symptoms can develop as a result of cumulative exposure to sustained headset use. In some call centre cases, this can occur without a specific acoustic incident being identified.

Acoustic Shock Symptoms

Typically, people experiencing an acoustic shock describe it like being stabbed or electrocuted in the ear. 

The initial symptoms can include some or all of the following:

  • A severe startle reaction, this may include a head and neck jerk
  • A stabbing pain in the ear
  • Tinnitus, hyperacusis
  • Sensations of burning, numbness, tingling, and a feeling of blockage or pressure in the ear
  • Sensations of muffled or distorted hearing 
  • Mild vertigo and nausea
  • Headache
  • A shock response: shaking, crying, disorientation, fatigue

Symptoms usually fade within a few hours or days.  In some cases, almost always associated with the development of hyperacusis, some of the symptoms can persist for months or indefinitely. Persistent symptoms are often sound-induced and can include:

  • pain in and around the ear
  • tinnitus
  • a feeling of pressure or fullness in the ear
  • pain/numbness/burning/tingling in the side of the neck/jaw/face
  • balance problems or unsteadiness
  • rarely, a hearing loss

Acoustic shock symptoms are involuntary, so they cannot be readily controlled, and subtle or subjective, so they cannot be easily objectively measured. The unusual symptom cluster may be misunderstood or not believed. Persistent symptoms are unpleasant, frightening and can be deeply distressing, potentially leading to a range of emotional reactions including trauma, panic attacks, anxiety disorders and depression.

Cause of Acoustic Shock Disorder Symptoms

The immediate cause of acoustic shock symptoms is considered to be excessive contractions of the middle ear muscles (stapedius and tensor tympani muscles), triggered by hearing the acoustic incident.  While the stapedial reflex is an acoustic reflex triggered by high volume levels, the tensor tympani reflex is a startle and ‘protective’ reflex with a variable threshold.

Persistent acoustic shock disorder symptoms are consistent with a condition called Tonic Tensor Tympani Syndrome (TTTS). With TTTS, the tensor tympani muscle is spontaneously active, rhythmically contracting and relaxing. This appears to initiate a cascade of physiological reactions in and around the ear.

Symptoms consistent with TTTS can include:

  • Tinnitus, often with a rumbling quality
  • Rhythmic sensations in the ears such as clicks and tympanic membrane (ear drum) flutter
  • Alterations in ventilation of the middle ear cavity leading to symptoms in the ears of a sense of blockage or fullness, frequent “popping” sensations (like a balloon popping) and mild vertigo
  • Minor alterations in middle ear impedance (stiffness) leading to fluctuating symptoms of muffled or distorted hearing
  • Irritation of the trigeminal nerve innervating the tensor tympani muscle. This leads to pain, numbness and burning sensations in and around the ear, along the cheek, neck and temporomandibular joint (TMJ) area.

Our Acoustic Shock Disorder Program

Our Audiology practice provides unique expertise in the evaluation and management of acoustic shock patients and in acoustic shock workplace consultancy.

Ms Myriam Westcott has been working with acoustic shock patients on a frequent basis since 2002. She is the most experienced audiologist internationally in the provision of acoustic shock evaluation and therapy. Myriam has extensive experience in the rehabilitation of tinnitus and hyperacusis, dominant symptoms of acoustic shock disorder.

Our evaluation and management program includes:

  • A definitive diagnosis
  • A hearing assessment
  • An evaluation of the emotional impact of acoustic shock disorder
  • Detailed and personalised explanations
  • A detailed report, including fitness for work, rehabilitation recommendations and referral for further evaluation and management

FAQs

Acoustic shock needs to be distinguished from and is different to cochlear (inner ear) damage from noise, also known as acoustic trauma, potentially causing a noise induced hearing loss.

Acoustic shock symptoms are usually temporary. Acoustic shock can become a disorder if hyperacusis develops. 

The neurophysiological symptoms associated with acoustic shock disorder are subjective, so cannot be objectively measured.

A carefully considered evaluation and diagnosis is made on the basis of the medical history noting acoustic incident exposure; the onset of symptoms consistent with acoustic shock following acoustic incident exposure; the pattern of symptom persistence and escalation over time; the development of hyperacusis; and any symptom exacerbation following exposure to intolerable (or difficult to tolerate) sounds.

Acoustic trauma from an intense sound wave can cause damage to the inner ear structures and rupture the tympanic membrane (ear drum). The tympanic membrane will usually heal over time.

Treatment of inner damage with steroid medication, either via intratympanic injections or orally, and hyperbaric oxygen therapy may be provided. However, permanent inner ear damage is likely.

The factors resulting in acoustic shock disorder leading to the development of hyperacusis are complex and outside a patient’s conscious control. Symptoms of pain can be treated and take priority.

Hyperacusis desensitisation is slow, requiring determination and belief in the prospect of change. Complete desensitisation may be difficult to achieve and an unrealistic expectation. However, partial desensitisation can make a big difference to symptom severity, and to the emotional impact and lifestyle constraints of acoustic shock disorder. 



Acoustic shock generally does not result in a hearing loss, although if present it tends not to follow the typical high frequency pattern of a noise induced hearing injury but affects low and mid frequency sensorineural and/or conductive hearing.  

Fluctuating symptoms of muffled or distorted hearing are common with acoustic shock disorder. A hearing assessment will identify significant hearing damage.



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