Journal Club: Specific change to DPOAE at 2kHz in a group of people with severe/profound misophonia

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Today's journal article

Suraj Urs BR, Nisha KV, Mohamad A, Prabhu P. Distortion-product otoacoustic emission input-output characteristics of misophonic ears with normal hearing. 

Why I picked this article

Misophonia is a condition in which certain everyday sounds, like chewing, breathing, or tapping, trigger intense irritation and discomfort, often causing emotional reactions such as anger, disgust and anxiety (https://en.wikipedia.org/wiki/Misophonia). The cause of misophonia is currently unknown. Because it is about the perception of sounds by the individual and hence based on subjective reporting, diagnosis of misophonia is challenging and is currently not defined. 

Often, people with misophonia have other auditory disorders such as tinnitus or hyperacusis. The changes in neural network-related sounds, including altered input from the peripheral auditory system, could be a contributing factor. In this research, researchers investigate the auditory function in patients with misophonia using the distortion product otoacoustic emissions input-output test (DPOAE I/O). DPOAE is a technique that allows assessment of the sound amplification by the cochlea, a physiological process that forms the basis for our cochlea to detect the smallest sounds. 


Some of the research findings

Participants & study design:

  • 60 participants (13 males and 47 females)
  • Misophonia group (30 participants, 2 males, 28 females, mean age 21 years old) 
    • Severity of Misophonia was assessed by Misophonia Assessment Questionnaire
    • Mild misophonia (16 participants)
    • Moderate/severe misophonia (14 participants)
  • Non-misophonia (30 participants, 11 males, 19 females, mean age 23 years old)
  • Exclusion: participants with ontological conditions such as hearing loss, tinnitus. 

DPOAE I/O testing

  • Sounds presented in 5-dB increments
  • Recorded on both ears for tones 1, 1.5, 2, 3, 4 and 6 kHz
  • "The intensity (L2) was varied from 45 dB SPL to 75 dB SPL, while the corresponding L1 was set according to the formula."
  • Responses at different intensity levels were compared. 
Finding: 
  • There was no difference between groups for DPOAE I/O slope. 
  • Comparison between non-misophonia, mild misophonia and moderate/severe misophonia groups showed some differences in the 2kHz DPOAE I/O test across broad sound levels. 
  • Some sound levels at 1kHz showed some difference, but the pattern was inconsistent. 
  • The difference was between the non-misophonia group and the moderate/severe misophonia groups, where the amplitude was consistently lower for the group of participants with moderate/severe misophonia. 
  • Researchers comment that this may suggest diminished cochlear sensitivity at a specific frequency only, and a similar pattern has been reported for people with tinnitus. 
  • Demographic representation between different genders was biased due to the fact that misophonia is more common in females than males. 

Haruna's takeaway

It looked subtle, but very interesting reporting about the DPOAE change was reported in the group with misophonia. There are "efferent" nerves that come from the brain and provide input to the cochlea and control sensory cell sensitivities. As researchers suggest in the discussion section, it may be that the input from the brain via efferent has changed in misophonia. If this can be investigated further, the cause of misophonia and a potential treatment option may be unveiled one day. 

Hearing disorders like misophonia, or other conditions like hyperacusis, musical hallucinations, are all hard to diagnose because it is based on the patient's being able to report what they are experiencing. More objective diagnostic tools can help lower the bar for patients to be diagnosed, and also raise awareness of the condition. Even if there may not be treatment, getting a diagnosis and acknowledgement of their condition could be very helpful and ease the distress of patients. We currently have very limited options for diagnosing hearing disorders, and that's why we need more research in the hearing space! 

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This is Haruna's 35/100 of the 100-day challenge to post a science blog article every day! I love inner ear biology & cochlear physiology.