Idiopathic sudden sensorineural hearing loss (i.e., unexplained unilateral sensorineural hearing loss with onset over a period of less than 72 hours) has an estimated incidence between 5 and 20 per 100,000 persons per year.1 This is likely to be an underestimate, since many who recover quickly never seek medical attention.2 Several large case series, including a total of approximately 7500 cases in the United States, Europe, and Japan,1,3,4,5,6,7,8,9,10,11 indicate that sudden sensorineural hearing loss typically occurs between 43 years and 53 years of age, with equal sex distribution.

Vestibular symptoms are present in 28 to 57% of patients. The likelihood of recovery of hearing has been reported to vary with the severity of hearing loss at presentation: patients with mild losses usually achieve full recovery, those with moderate losses often show some spontaneous recovery but seldom have a full recovery unless treated, and those with severe-to-profound hearing losses rarely show spontaneous improvement or make a full recovery.1,4,12 The prognosis for recovery of hearing also seems to be worse in older patients and those with associated vestibular symptoms.1,3,4,5 Approximately 1% of cases of sudden sensorineural hearing loss are due to "retrocochlear" disorders that may be related to vestibular schwannoma, demyelinating disease, or stroke.3 Another 10 to 15% are due to another identifiable cause, such as Meniere's disease, trauma, autoimmune disease, syphilis, Lyme disease, or perilymphatic fistula.4,5,13,14 The remainder are idiopathic and almost exclusively unilateral. Rare cases of bilateral sudden deafness most often reflect a psychiatric ("functional") cause or a neurologic process (e.g., neoplastic dural infiltration of the posterior cranial fossa, paraneoplastic syndrome, or encephalitis); transient bilateral sudden sensorineural hearing loss may also result from a sudden drop in intracranial pressure during a spinal tap or after intracranial surgery. A common problem in sudden sensorineural hearing loss is delay in diagnosis. Ear fullness, a common presenting symptom, is often attributed by patients and clinicians to impaction of cerumen or congestion from upper respiratory illness or allergies.

Insofar as evidence suggests that permanent hearing loss is more likely when treatment is delayed, it is important that a diagnosis of sudden sensorineural hearing loss be considered and prompt referral made to physicians with expertise in otolaryngology.