|MadSci Network: Anatomy|
Hearing loss can be grouped into two general categories: Conductive and Sensorineural. An audiogram including air and bone conduction thresholds will help differentiate them. Tuning fork tests such as the Webber and Rine test are clinical tests many physicians can perform in the office to give some indication of the type of hearing loss.
Sudden conductive hearing loss is usually caused by some type of traumatic incident that either ruptures the ear drum or disarticulates the bones that conduct sound from the ear drum to the cochlea. Other causes can be temporal bone (skull) fractures or acute otitis media (infected fluid behind the ear drum limiting its movement). Again all of these cause acute (onset in hours to days) hearing loss from sound not being conducted to the cochlea properly.
Sensorineural hearing loss is a problem in converting the sound that reaches the cochlea into nerve signals or transmitting/processing those nerve signals in the brain. The causes of sudden sensorineural hearing loss are often much more elusive. Acoustic trauma (concerts, gunfire, etc.) can cause temporary or permanent sensorineural hearing loss and are thought to primarily involve damage to hair cells which converts sound energy into nerve signals. Some medications (lasix, aspirin, aminoglycoside antibiotics) can cause temporary or permanent sensorineural hearing loss. These each affect different parts of the cochlea. Episodic hearing loss with tinnitus and vertigo is often the result of meniere's disease, but can also be caused by perilymphatic fistulas. There is a clinical entity called "sudden sensorineural hearing loss" in which the above causes have been excluded and the cause is thought to be some form of autoimmune, viral or circulatory disorder. Different treatment protocols have included high doses of steroids (either oral or injected through the ear drum), bed rest, antivirals, and blood thinners among other things. A subset of these respond very well to steroids, especially if treated quickly (within days). Some resolve on their own, and some of those who respond to steroids have their hearing loss returns as the steroids are tapered. This group is said to have steroid dependent sudden sensorineural hearing loss, and is thought to be caused by an autoimmune disorder.
So the simple answer is: Lots of things can cause a sudden hearing loss. In many of these the hearing loss will resolve, while many will not. If you have a sudden hearing loss you should seek help from a qualified physician and will likely need to see a specialist (an Otolaryngologist).
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