what causes sudden hearing loss

Sudden hearing loss (SHL) is defined as greater than 30 dB hearing reduction, over at least three contiguous frequencies, occurring over a period of 72 hours or less. Some patients describe that the hearing loss was noticed instantaneously in the morning and others report that it rapidly developed over a period of hours or days.

The severity of the hearing loss however varies from one patient to another and only one ear is usually affected. Sudden hearing loss frequently involves both ears (Schreiber et al 2010). Tinnitus is usually reported in patients with SHL loss and vestibular symptomsare present in roughly 40% of cases (Mattox & Simmons 1977). The incidence of SHL has been reported to be 5-30 per 100,000 person per year (Nosrati-Zarenoe et al 2007, Wu et al 2006)and accounts for 1% of all sensorineural hearing loss cases (Hughes et al 1996). Males are equally affected as females. The average age at onset is reported to be 46 to 49 years with increasing incidence with age (Byl 1984).

There are many causes for sudden hearing loss which include infectious, circulatory, inner ear problems like meniere’s disease, neoplastic, traumatic, metabolic, neurologic, immunologic, toxic, cochlear, idiopathic (unknown cause) and other causes. Unfortunately, even after a thorough search for a possible pathology, the cause of sudden hearing loss remains unknown in most patients (Hughes et al 1996).