Idiopathic sudden sensorineural hearing loss (sudden deafness) accounts for approximately 1% of all cases of sensorineural hearing loss, and is unfortunately a condition in which the etiology has not yet been clearly determined. Sudden deafness can be defined as a hearing loss that either occurs in an instant, or that progresses rapidly over a few days.
The hearing loss is usually unilateral, varying from a mild to a profound deafness, and is most frequently noticed on arising in the morning. In addition to the hearing loss, the patient may complain of tinnitus and a mild feeling of imbalance, although severe vertigo is usually not a feature of this syndrome.
Some recovery occurs spontaneously in approximately 50% of cases. Several factors have been found to be of value in predicting the extent of recovery from idiopathic sudden sensorineural hearing loss. A profound sensorineural loss, severe vertigo, electronystagmographic abnormalities, loss of the acoustic stapedial reflex, and the absence of tinnitus are all factors that have been associated with a poor prognosis for the return of hearing.