Idiopathic Sudden Sensorineural Hearing Loss (ISSHL) is defined as hearing loss of at least 30dB occurring within 3 days over at least three contiguous frequencies.1
The most common clinical presentation involves sudden unilateral hearing loss, tinnitus, aural fullness and vertigo. The incidence is estimated at 8-15 per 10,0000 worldwide.2
There are currently over 100 publications available evaluating the use of hyperbaric oxygen therapy (HBOT) for treatment of ISSHL, including eight randomised control trials and a Cochrane meta-analysis.
On average, HBOT has been shown to impart a 19.3dB gain for moderate hearing loss and 37.7dB gain for severe cases. 3 This improvement brings hearing deficits from the moderate/severe range into the slight/no impairment range, a significant gain that can markedly improve a patient’s quality of life.
There is currently no consensus over the aetiology of ISSHL, with suggested mechanisms including vascular occlusion, ischemia, viral infection, labyrinthine membrane breaks, immune associated disease, abnormal cochlear stress response, trauma, abnormal tissue growth, toxins, ototoxic drugs and cochlear membrane damage. 4
The rationale for the mechanism of action for HBOT in ISSHL is likely due to the high metabolism and vascular paucity of the cochlea. Tissue oxygenation of the cochlear structures occurs via diffusion from cochlear capillary networks into the perilymph and cortilymph.
Perilymph oxygen tension has been shown to decrease significantly with ISSHL. 5 Animal studies have shown that compared to room air, normobaric oxygen increases perilymph PO2 3.4 fold, while HBO2 increases perilymph PO2 9.4 fold. 6 However, only HBO2 has been shown to achieve extremely high arterial perilymphatic oxygen concentration gradients in both animals and humans. Other additional postulated benefits include anti-inflammatory effects, blunting of ischemia reperfusion injury and oedema reduction.
When ISSHL is diagnosed, immediate referral to an ENT surgeon should occur. Oral steroids at 1mg/kg/day is a common initial dose tapering over the course of 2-3 weeks.
HBOT has been shown to be most effective if delivered within 2 weeks of hearing loss, with benefit possible up to 3 months post insult.7,8 Patients with a delay of greater than 14 days, advanced age and vertigo are however associated with poorer outcomes. 8
The Cochrane analysis of HBOT for ISSHL has shown a NNT of 5.3.3
A typical treatment regimen is of 10-15 treatments breathing 100% oxygen at 2.4ATA, during which routine pure tune audiometry is undertaken on a weekly basis to track changes in hearing acuity as a response to the treatment.
There is no medicare item number for treatment of ISSHL at this point in time, but the treatment is covered by Alliance health funds so there is no out of pocket expense for their clients.
Our unit will happily asses any referred patient with ISSHL. We can then discuss options and undertake treatment if required.