Sudden deafness – The how and why

Have you ever been unfortunate to suddenly lose your hearing, or know of someone who had? This is a disaster if it should happen. Thankfully the likelihood is very uncommon and estimated to happen to 12 out of every 100, 000 persons each year. Nonetheless this condition has a name - it is commonly called sudden sensorineural hearing loss and is regarded as one of the few medical emergencies of the ear.

Why does it happen? There are many reasons why we might suddenly lose our sensorineural hearing. The easiest way to understand this is to consider what could damage our hearing pathway from our inner ear to our auditory nerve (nerve of hearing) and to our auditory cortex, the part of the brain that interprets sound. Sufferers often claim they wake up with reduced or no hearing, or pressure in the ear with a ringing noise, with the hearing gradually getting worse without recovery. This sudden loss of hearing may or may not be accompanied by a sense of unbalance, dizziness, nausea and vomiting. Sometimes there is ear pain with a painful rash around the affected ear.

It should be said that some obvious causes do not come under this medical label of sudden hearing loss even though hearing loss may be a result. This includes history of trauma to the head which can cause concussion and/or bleeds in the brain as well as shock and fracture damage to the cochlea. Surgery to the ear and/or brain for other conditions, may also cause hearing loss. This causes are obvious and treated accordingly.

So what are the possible causes that are not so obvious? At the cochlear and auditory nerve level, viruses have been often cited as a cause especially the Herpes family of viruses. A herpes zoster infection, which is the same as secondary chicken pox viral infection or shingles, can cause an inner hearing loss with a painful shingles rash on the ear and face. Bacterial infection e.g. syphilis, of the cochlear is very rare and patients are usually very sick. Diabetes mellitus has also been said to be a cause. This condition is known to cause small vessel disease, blocking the vessels that feed the cochlea, and hence it dies. Similarly, autoimmune conditions in general are thought to also cause vessel blockage and nerve tissue inflammation, which can damage the cochlea and the auditory nerve. As there are many types of autoimmune diseases, identifying the hearing loss as due to that possibility usually starts the diagnostic process for that autoimmune condition.

Tumors are sometimes the cause of the sudden hearing loss. This is often what the patient fears the most, yet it is even less likely to occur and much easier to diagnose with highly sensitive magnetic resonance imaging of the brain today. The commonest tumor grows from the nerve lining of the auditory nerve. These tumors are called acoustic neuromas and occur in 2-3 out of every 100,000 Hong Kong persons each year. They are almost always benign and grow very slowly. However, as the auditory nerve passes through a narrow bony canal to get to the brain, it can get compressed even with a small growth, starving and paralyzing the auditory nerve and causing hearing loss.

When a patient seeks a medical consultation for sudden hearing loss, it is important to diagnose the reason and to offer the correct treatment. A hearing test is mandatory after a complete ear examination and can confirm or refute cochlear hearing loss. If it is confirmed that a sudden hearing loss event has occurred, then the diagnosis should be established if possible. A battery of tests to view the blood profile, kidney function, inflammatory blood markers, thyroid function, the fasting glucose and cholesterol profile as well as a magnetic resonance imaging of the brain and auditory nerve, are usually performed to seek the cause. Unfortunately, or fortunately, the cause is not usually found with this test battery screen. The true-positive hit rate of this test battery for a diagnosis is about 0.1% i.e. 1 out of every 1000 patients screened. Hence most of the time, the diagnosis is idiopathic sudden sensorineural hearing loss, which is to say we have search for all possible diagnoses but cannot establish one as yet. Nonetheless the test battery is important as it screens for treatable conditions. Understandably the sufferer may not be satisfied that a cause cannot be clearly established. However, in the absence of a clear diagnosis, hearing rescue treatment can still and is given, and this will be discussed later.

The final take home message for readers is that sudden hearing loss is regarded as a medical emergency as the available evidence–based medicine research shows that early treatment within two weeks of the hearing loss event has the best chance of recovery. So here, early medical attention is the rule. If in doubt, do not be. Seek medical advice early.

The Chinese version of this article was published in Hong Kong Economic Journal on 20 Jun 2016 and 4 Jul 2016