What is SSNHL?
Sensorineural hearing loss is when the cochlea (sensory part) or the hearing nerve (neural part) is damaged or malfunctions. Sudden or rapidly progressive hearing losses fall under a single definition. But they are based on severity, period of time, hearing test criteria and the frequency spectrum of the loss.
- Waking with a hearing loss
- losing hearing over a few days
- selective low- or high-frequency loss, and
- distortions in speech perception.
SSNHL is determined by a loss of greater than 30dB over three contiguous pure-tone frequencies, over a three-day period.
It rarely occurs in both ears. But it is frequently accompanied by tinnitus (70%), vertigo (50%), aural fullness, headaches or vision changes.
What causes SSNHL?
Sudden deafness has many possible causes, but for the majority of cases the specific cause cannot be identified (idiopathic). There are several theories about what is behind the development of SSNHL. But none individually can account for all SSNHL types.
The three most prevalent theories are a:
- recent viral infection that may have damaged the cochlea;
- vascular compromise that may have altered the blood flow to the cochlea. The cochlear is very sensitive to changes in blood supply;
- rupture of the delicate membrane that separates the inner ear from the middle ear. Or the membrane in the cochlea that separates the fluid-filled perilymphatic and endolymphatic spaces may have increased pressure. This pressure could be from within (cerebrospinal fluid) or without (middle ear pressure); resulting from straining or changes in barometric pressure from flying or scuba diving.
Is SSNHL common?
The average incidence of SSNHL is about 5 to 20 per 100,000 people per year. However, it is probably much higher as many cases go unreported with spontaneous recover and no medical intervention. The estimates for unreported SSNHL are around 65%. The condition is multifaceted and occurs across all age groups, male and female. Fewer cases are reported in children and the elderly though. And young adults have similar incidence rates to middle-aged adults. The average age of those who seek medical attention is 40-54 years.
Is SSNHL temporary?
The hearing loss may be temporary or permanent. SSNHL is considered to be a medical emergency, so it is wise to seek medical attention as soon as possible as this ensures a better chance of recovering the hearing. The urgency depends upon the hearing loss being sensorineural or conductive (caused by a blockage or damage to the outer and/or middle ear) – a GP can check this with a simple tuning fork test. A sensorineural loss requires urgent referral to an ENT or better still a hospital emergency department.
How is treatment determined?
Every case is different and there is no clear cut diagnosis. The first step is a thorough search for potentially treatable causes. This is done by undertaking an exhaustive patient medical history to reveal any risk factors for hearing loss and a thorough physical examination. This should include questions about recent events like air travel, strenuous exercise, weight-lifting, diving, falls, other head trauma, viral illnesses, respiratory infections, fevers, previous ear surgery, medications and exposure to pesticides.
On the basis of any findings, carefully selected laboratory and radiographic investigations are then made. Lab tests might look for infection, thyroid disease, diabetes, autoimmune diseases, syphilis or high cholesterol. An MRI with an injection of dye to better see small structures in the ear is the standard test for checking for skull base tumours like acoustic neuromas, especially as a 30-40% false-negative rates exists with auditory brainstem response testing (if hearing levels permit). About 1-2% of patients have an internal auditory canal tumour. CT scans are generally not recommended in the initial evaluation unless the SSNHL may be trauma-induced.
Audiometry is mandatory including pure-tone and speech tests and immittance (tympanometry and acoustic reflex) tests. Auditory brainstem response testing and otoacoustic emissions tests may provide additional information regarding the functional integrity of the auditory system.
Vestibular (balance) tests may also be done. Even with all these tests, doctors may still not be able to ascertain the process within the body that resulted in the hearing loss.
What is the treatment for SSNHL?
Attempts to treat SSNHL are difficult because the exact cause of the condition is often unknown. As a result, treatment regimes are varied and dictated by the factors revealed in the patient history, physical examination and test results. Determining which treatment modalities are the most effective is also difficult due to the relatively high rate of spontaneous recovery.
Various classes of treatment are available but none have been conclusively proven to be effective. The most popular treatment is anti-inflammatory corticosteroids – firstly with oral prednisone followed by injecting dexamethasone into the middle ear cavity for patients with severe to profound SSNHL who do not improve on the oral steroids. Sometimes hyaluronic acid may also be injected into the cavity to increase the permeability of the membranes and the distribution of the steroid in the inner ear.
Other classes of treatment include vasodilators to improve blood supply to the cochlea and reduce vascular spasms; anticoagulants to improve blood flow; diuretics under the assumption that episodes of idiopathic SSNHL are secondary to endolymphatic hydrops (Ménière’s disease) that refers to a condition of increased hydraulic pressure within the inner ear endolymphatic system; anti-viral agents; triiodobenzoic acid derivatives; and hyperbaric oxygen. Occasionally surgery may be recommended to repair an inner ear membrane tear.
Follow-up audiometry within six months of diagnosis should be obtained and patients who do not fully recover their hearing should consider aural rehabilitation and hearing aids or the use of an assistive listening device.
What outcome can be expected?
It is difficult to accurately predict the outcome of SSNHL. Primarily because of the low incidence of the condition and the unpredictability of its natural causes. However, patients who seek medical treatment within 7-10 days after onset of the hearing loss do better than those who wait 30 days or more. The severity of the hearing loss is inversely proportional to the rate of recovery. Patients with a mid-frequency loss do better than those with high-frequency loss. Poorer recovery rates have been recorded for patients with vertigo. The intensity of the vertigo roughly correlates with the degree of hearing loss. Elevated ESR levels (a screening test that measures the sedimentation rate of red blood cells and can pick up inflammatory diseases) also signals a poorer prognosis. Patients with normal hearing in the other ear do better.
Bettina Turnbull, an audiologist, professional development manager for Connect Hearing and vice-president of the Australian College of Audiology shares her recent frightening experience of SSNHL.
Recently, totally out of the blue I lost my hearing in one ear. Thankfully it has returned but it was frightening as there was a possibility that I could have ended up with permanent single-sided deafness.
As a hearing person who works with hearing-impaired patients it was a particularly eye-opening experience and I now have a much better understanding of how you actually “feel” when you have compromised hearing.
It happened at a training meeting. One of my ears blocked up and I started to hear an intermittent “chirp, chirp” sound like crickets at night. It was a very busy period and I thought a quite weekend and sleep would sort it out, but a few days later the same thing happened at another training meeting. Only this time is was much worse with nausea and light-headedness where I couldn’t focus my thoughts.
Surrounded by audiologists, I had my hearing tested to confirm I wasn’t imagining the hearing loss. Promptly taking myself off to Melbourne’s Eye and Ear Hospital emergency department, I was seen by an ENT who diagnosed idiopathic SSNHL. I’m not sure why hearing loss but she suspected the cause was a virus. I was prescribed a fortnight-long high-dose course of the oral steroid prednisone and was advised not to fly for two weeks other than to get back home to Sydney (as flying stresses the ear and body).
I was told to rest and I now understand why. Taking steroids at such a high dose was quite an experience – it’s like having your blood rush around your head at 20 times the speed it should and the side effects include anxiety and insomnia.
I was totally surprised at how difficult it was to hear in a noisy place, even with one good ear. I felt disorientated, frustrated and my brain had to work ten times harder to concentrate on hearing what was being said. (For audiologists, this is an area we perhaps underestimate and should talk about with patients rather than just focusing on volume, clarity and functions.)
I was also terrified that my hearing may not return and anxious to investigate further what may have caused the hearing loss.
Once home I contacted my local ENT who organised an immediate MRI to check my inner ear structures were normal, which they were thankfully. He then injected another steroid – dexamethasone – into the middle ear space to be absorbed through the round and oval windows. This was done with a needle after anesthetising the tympanic membrane (eardrum). I was told to go home and lie on my good side for maximum absorption of the drug into the cochlea. Five days later I had another hearing test and things were very much improved. A week later my ENT repeated the injection treatment.
I am so relieved my hearing has returned. I still get ‘overload’ twang when sounds are quite loud but otherwise all sounds normal now.
This article on SSNHL originally appeared in Hearing HQ magazine in Dec 2013.