Acoustic Trauma

Acoustic trauma is sudden sensorineural hearing loss and tinnitus after exposure to an intense sound, such as an explosion, gunshot, firecracker or loud concert. It differs from slowly progressive noise induced hearing loss.

It is common among military personnel, shooters, musicians and young people. About 10% to 30% of noise exposure cases develop permanent loss. Hearing loss typically affects 3 to 6 kHz first, with a notch at 4 kHz, and may recover partly over days.

Pathophysiology.

Intense sound causes mechanical damage to hair cells, supporting cells and the stria vascularis, with oxidative stress, calcium overload and loss of ribbon synapses. Damage of outer hair cells accounts for loss of sensitivity.

Hearing loss and fullness, tinnitus, muffled sound, hyperacusis and sometimes vertigo, immediately after the exposure. Drum perforation or ossicular disruption is possible after blast.

Red flags.

• Profound unilateral sensorineural loss.
• Vertigo or facial weakness.
• Blood from the ear, or head injury.
• Cerebrospinal fluid leak.

Otoscopy checks for tympanic membrane perforation or haemotympanum. Pure tone audiometry as soon as possible (the same day or within 48 hours) shows sensorineural loss, typically with a notch at 3 to 6 kHz, and compares it with the other ear and any earlier tests. Tympanometry and otoacoustic emissions help. Magnetic resonance imaging of the internal auditory meatus is done for asymmetric loss that does not recover.

Differential diagnosis.

• Sudden idiopathic sensorineural hearing loss.
• Barotrauma and perilymph fistula.
• Ménière disease.
• Vestibular schwannoma.
• Ototoxic drug effect.
• Cogan syndrome.

Remove the person from noise and protect against further exposure. Give corticosteroids early (within 7 days, best within 72 hours). Offer salvage intratympanic steroid if there is poor recovery after 1 to 2 weeks. Hyperbaric oxygen is an option in specialist centres. Treat tinnitus with sound enrichment and counselling.

• Prednisolone: 1 mg/kg orally once daily (usually 60 mg; maximum 60 mg) for 7 days, then taper over 7 to 10 days; monitor glucose, blood pressure, mood and sleep; reduce in older adults, and give gastric protection; use with caution in diabetes.
• Dexamethasone (intratympanic, salvage): 4 mg/mL, 0.4 to 0.6 mL into the middle ear, three injections over 7 to 10 days; maximum 3 injections; monitor for pain, dizziness and perforation; avoid with an active infection.

Advise hearing protection (earplugs or earmuffs) in future exposure, and avoid further noise for 2 weeks.

Monitoring. Audiometry at 1 week, 1 month and 3 months.

Referral and escalation. ENT and audiology urgently.

Special groups. Pregnancy: use steroids when the benefit outweighs the risk, with glucose checks.