Sudden Hearing Loss

In most people, no cause can be found for their sudden hearing loss. However, doctors have several theories. Possible causes include viral infections (particularly infections with herpes simplex virus), an attack on the inner ear or its nerves by the body's immune system (autoimmune reaction), and blockage of the small blood vessels of the inner ear or the blood vessels of its nerves. Perhaps different causes affect different people.

In many other people, a cause for the sudden hearing loss is obvious. Such causes include

• Head injury

• Severe pressure change

• Drugs that damage the inner ear (ototoxic drugs)

• Infections

Head injury (such as a fracture of the temporal bone in the skull or sometimes a severe concussion without a fracture) can damage the inner ear and cause sudden hearing loss.

Severe pressure changes (such as those that can occur with diving or less often by bearing down during weightlifting) can cause a hole (fistula) to form between the middle and inner ear. Sometimes, such a fistula is present from birth and can spontaneously cause sudden hearing loss or make the person more susceptible to hearing loss after a head injury or pressure changes.

Ototoxic drugs are drugs that have damaging side effects to the ears. Some drugs can rapidly cause hearing loss, sometimes within a day (especially with an overdose). A few people have a rare genetic disorder that makes them more susceptible to hearing loss from the class of antibiotics called aminoglycosides. All people taking such antibiotics should have blood tests while on the drug to screen for toxic levels that can cause hearing loss. People receiving drugs that are excreted in the urine, such as aminoglycosides, should also have their kidney function checked and monitored to avoid kidney damage.

A number of infections cause sudden hearing loss during or immediately after acute illness. These infections include bacterial meningitis, Lyme disease, and many viral infections. The most common viral causes in the developed world are mumps and herpes simplex brain infection. Measles is a very rare cause because most people are immunized against the infection.

Sudden hearing loss rarely can be the first symptom of some disorders that usually have other initial symptoms. Such disorders include a tumor of the auditory nerve called acoustic neuroma, multiple sclerosis, Meniere disease, or a small stroke due to a blockage of a branch of the artery that goes to the balance center of the brain (the cerebellum). Sometimes a syphilis infection reactivates in people who have HIV infection. This reactivation can cause sudden hearing loss.

Rarer disorders include Cogan syndrome, in which an autoimmune reaction attacks the inner ear (and also the surface of the eye); certain disorders involving blood vessel inflammation (vasculitis); and blood disorders such as Waldenström macroglobulinemia, sickle cell disease, and some forms of leukemia.

Sudden hearing loss is itself a warning sign.

Anyone with sudden hearing loss should see a doctor right away because some causes must be treated quickly. If symptoms of dysfunction of the nervous system other than hearing loss are present, hearing loss may be a symptom of nerve or brain dysfunction.

Doctors first ask questions about the person's symptoms and medical history. Doctors then do a physical examination. What they find during the history and physical examination may suggest a cause of the sudden hearing loss and the tests that may need to be done.

Doctors note whether hearing loss affects one or both ears and whether a specific event such as head injury, diving injury, or infectious illness occurred. They ask about accompanying symptoms that involve the ear (such as ringing in the ears or ear discharge), balance center (such as disorientation in the dark or vertigo), and other parts of the brain and nervous system (such as headache, weakness, or an abnormal sense of taste). They try to identify whether people are currently taking (or recently took) any ototoxic drugs.

The physical examination focuses on the ears and hearing and on examination of the nervous system.

Typically, people should have an audiogram (a hearing test). Unless doctors think the problem is clearly an acute infection or drug toxicity, they usually also do gadolinium-enhanced magnetic resonance imaging (MRI) or computed tomography (CT), particularly when the hearing loss is greater in one ear. Other tests are done based on the likely cause. For example, people who had a head injury should have MRI. People at risk of sexually transmitted infections should have blood tests for HIV infection and syphilis.