By: Sean Lennox
Acoustic shock disorder (ASD) is a little known syndrome that can follow abrupt loud noise exposure. I didn’t learn about this syndrome until I met patient A.W. last year and I was left searching for answers as she suffered from the effects of loud noise exposure. Please be advised that this is not a typical hyperacusis or tinnitus case and the interested audiologist should search the current literature themselves prior to suspecting ASD as a final diagnosis Patient R.A. is a 40 year old female call centre employee that works for a major cell phone company. Her initial consultation occurred November 12th, 2010. She reported a sudden significant hearing loss on her right side that is accompanied by a plugged sensation, hyperacusis, and distressing humming tinnitus. She also experiences bouts of vertigo that last for about an hour and she has been experiencing them about once a day. She reports that the onset of her symptoms coincided with a brief loud squawking sound that was emitted from her headset during a call to a client September 12th, 2010. The loud sound lasted around 3 seconds as she tried to frantically remove the headset. Peak output of the telephone headset was measured using a sound level meter with a fast response at 128dBA. She immediately experienced a plugged sensation on her right side followed by the humming tinnitus that lasted the rest of the day. She reports that the hearing loss didn’t occur until the following morning and the first episode of vertigo was experienced that evening. Since impact noise exposure incident she reports intermittent stabbing otalgia, increased anxiety when in even low levels of ambient noise, and a hypersensitivity to loud sounds and certain pitches of sound.
At the initial visit R.A. was found to have a moderate low frequency rising to normal at 2 KHz SNHL on the right side. Right ear immittence and acoustic reflexes were normal and speech discrimination was degraded to 70%. Additional electrophysiological tests of brainstem and auditory nerve function were found to be normal bilaterally. Her loudness discomfort levels were between 65-80dB overall which is considerably lower than expected. A physiologic test of outer hair cell function was inconclusive because of ambient noise. A tinnitus evaluation was done 2 weeks later on Nov 28th 2010 (see appendix), and she matched the tinnitus to 500Hz pure tone at 3 dB SL. MML level using broad band noise was 45dB HL. Residual inhibition was negative. Given these results, I was not confident in attributing her hearing loss and accompanying symptoms to a transient loud noise exposure, and I wanted to rule out Endolymphatic hydrops, and specifically Meniere’s disease. I stated that we needed to monitor over the next 2 months to check for symptom stability as it was only 2 months since the acoustic trauma occurred. In the interim she had a Videonystamography (VNG) assessment done which showed normal oculomotor and vestibular function bilaterally. A consult with an Otolaryngologist was scheduled and he ruled out Meniere’s based on the information provided to him and patient history. He agreed that the audiologic profile did not match the typical noise induced hearing loss audiometric configuration. An audio done January 12th, 2011 ( see appendix) showed a stable low frequency SNHL on the right side and she was still reporting a fullness on the right side, bothersome unilateral tinnitus, otalgia, hyperacusis, phobia of loud sounds, and vertiginous episodes every week or so.
Confirming the stability of the aural symptoms encouraged me to consult the current literature on the likelihood that a transient noise exposure could have contributed to the hearing loss and cluster of symptoms she was experiencing. A thorough literature search brought me to a syndrome called Acoustic Shock Disorder / Syndrome (ASD). ASD is a cluster of symptoms including: “…otalgia, altered hearing, aural fullness, imbalance, tinnitus, dislike or even fear of loud noises, and anxiety and/or depression” (McFerran and Baguley, 2007) following an acoustic trauma from a transient loud sound. The otalgia, dizziness, plugged sensation, hyperacusis, general anxiety/depression and phobia to sound in the affected ear was highlighted in many studies (McFerran and Baguley, 2007; Westcott, 2006; Milhinch, 2002) although hearing loss for ASD is not as predictable and tends to fully recover (Lawton, 2003; Milhinch, 2002). Most of these symptoms have been attributed to the prolonged dysynchrony of the tensor tympani and stapedius muscle reflexes (Westcott, 2006; Milhinch, 2002) which are associated with the
physiologic startle reflex (Mcferran and Baguley, 2007).
At her 1 year post-noise exposure visit her hearing on her right ear returned to normal. However, she still experiences the symptoms of hyperacusis, tinnitus and aural pressure however at a diminished level. She was still suffering from a general phobia of loud sounds and reported she could not return to work especially in a noisy work environment.
Lawton, BW, (2003). Audiometric Findings in Call Centre Workers Exposed to Acoustic Shock. Proceedings for the Institute of Acoustics. Vol 25 ; 3.
McFerran DJ and Baguley DM. (2007): Acoustic shock. Journal of Laryngology and Otology. 13: 133-134.
Westcott, M. (2006). Acoustic Shock Injury (ASI). Acta Oto-Laryngologica Vol.126; 54-58
Milhinch (2002). Acoustic Shock Injury: Real or Imaginary? Audiologyonline.com. http:// www.audiologyonline.com/articles/article_detail.asp?article_id=351 (accessed July 2011)