Intratympanic Injection of Dexamethasone With Hyaluronic Acid in Treatment of Sudden Sensorineural Hearing Loss

Sudden sensory neural hearing loss (SSNHL) is defined as sensorineural hearing loss of at least 30 dB over 3 consecutive frequencies within 3 days. Different treatment modalities have been used in treatment of SSNHL including systemic corticosteroids alone or in combination with vasodilators as pentoxifylline and hydroxyethylstarch (HES) or low molecular weight dextran, hyperbaric oxygen therapy \& plasmapheresis. Intratympanic (IT) dexamethasone application has shown significantly higher perilymph steroid concentrations with lower systemic concentrations, thus avoiding the side effects associated with the systemic route. It has been used with varying results for the treatment of Meniere's disease, SSNHL, low frequency hearing loss and tinnitus. After IT injection, the drug concentration in the inner ear depends on the drug being in contact with the round window membrane (RWM), absorbing it from the middle ear into the inner ear. However, large amount of the injected drugs are either absorbed by the middle ear mucosa or evacuated via the eustachian tube. It has been postulated that combining the drug with a biodegradable material will prolong its availability in the middle ear and/or aid its diffusion across the RWM. Between these materials, Hyaluronic acid (HA) is a natural product normally present is humans' perilymph in small amounts along with many other tissues throughout the body. Several postulations have been given to HA mechanism of action in drug delivery in the middle ear either by its osmotic effect on the perilymph, modulating RWM permeability or altering blood viscosity thus increasing blood and oxygen delivery.