Sudden hearing loss

The definition of sudden hearing loss is widely accepted as a sensorineural hearing loss of 30 dB or more, over at least three contiguous audiometric frequencies, that develops over 3 days or less. It must either be a new loss occurring in an ear with previously normal hearing or an incremental deterioration in an ear with pre-existing hearing loss. Although conductive hearing loss may also be sudden, with middle ear effusion as the most common cause, the term sudden hearing loss specifically refers to sudden sensorineural hearing loss. Its low incidence (eight per 100 000 persons per year), heterogeneous pathologies and spontaneous recovery (50% of patients) mean that few controlled studies exist. Comparisons are made difficult by diverse inclusion criteria and outcome measures, leading to a myriad of treatment protocols. In all, 5–10 % of sudden hearing loss cases are because of identifiable causes, which may be infectious, traumatic, neoplastic, auto-immune, toxic, circulatory, neurologic and metabolic. The overwhelming majority of cases are idiopathic, with labyrinthine viral infection, vascular insult, intracochlear membrane rupture, autoimmune inner ear disease and activation of cochlear nuclear factor kappa B (NFjB) proposed as possible causes.