Sudden Sensorineural Hearing Loss

Imagine waking up one morning and feeling like the speakers have been switched off on one side of the house. In some cases, the entire sound system fails, with sounds through both sides reduced to a muffled mumble. Sudden sensorineural hearing loss (SSHL) can be an alarming event- one moment you’re experiencing the world in surround sound and the next you’re watching a silent film.

SSHL is an inner ear condition involving sudden loss of at least 30 decibels over at least three consecutive frequencies within a period of 72 hours. If normal speech volume is 60dB and whispering is half that, SSHL at its minimum reduction in hearing for this diagnosis means suddenly every conversation feels like someone is telling you a secret in hushed tones.

In the US, around 66,000 new cases of SSHL are diagnosed every year. The vast majority of cases occur just in the one ear (unilateral), though around 2% of affected individuals will find themselves watching a silent film due to bilateral hearing loss in both ears. Any age group can be affected though the prevalence of SSHL peaks around the fifth and sixth decade; both males and females are equally affected.

What Causes SSHL?
Though the number of potential underlying causes for SSHL are typically quoted as being over a hundred, up to 90% of patients with SSHL will actually not have an identifiable cause, meaning their hearing loss is considered idiopathic. One meta-analysis of various studies found the most common categories of SSHL causes were infectious, otologic (relating directly to the anatomy and function of the ear itself), traumatic, vascular (involving blood or the blood vessel system), and neoplastic (involving a tumor). In many cases of SSHL, identifying the underlying cause of the hearing loss is important not only to treat the hearing but also to address the underlying disorder, which can often be more serious in its consequences than the hearing loss.

In the US, the most common bacterial infections known to result in SSHL are Lyme disease and syphilis. Lyme disease is transmitted via the bite of a tick and is considered endemic throughout North America. The bacteria can cause other neurological symptoms throughout the body, including facial paralysis and fibromyalgia, as well as secondary conditions such as arthritis and atrioventricular block. Regarding syphilis infections, we all already know how that is transmitted but you probably have never heard of the term otosyphilis. In addition to SSHL, syphilis infection of the ear can induce fluctuating and progressive hearing loss, tinnitus, and attacks of vertigo.

Other causes of SSHL include:

  • Viral infection, including herpes, rubella, HIV, the flu, and mumps
  • Otologic disorders such as Meniere’s disease, otosclerosis, and an enlarged vestibular aqueduct
  • Trauma, which is often reasonably easy to identify. However, some cases of SSHL may result from very mild trauma, such as jumping into a pool, an event which does not immediately come to mind during presentation. Traumatic causes can also come from medical procedures such as surgery
  • Vascular and blood-related conditions, such as sickle cell anemia, strokes, and subdural hematoma (bleeding between the outer layers of the brain). These conditions reduce blood flow to the cochlea of the inner ear, which can be very sensitive to oxygen deprivation
  • Neoplasms, including acoustic neuromas
  • Ototoxic medications, which can damage hearing, such as aminoglycoside antibiotics, chemotherapy medications, and non-steroidal anti-inflammatory drugs
  • Systemic autoimmune diseases, such as lupus and thyroid dysfunction

 
Treatment and Prognosis of SSHL
As one of the indicators of a better prognosis for SSHL is timely treatment, patients who experience sudden hearing loss should see an appropriate medical professional immediately. High-dose oral steroids, such as prednisolone, when administered within the first two weeks of the onset of SSHL provide the best chance of improvement; however, around 45-65% of idiopathic SSHL have been known to spontaneously recover some degree of hearing within the first couple of weeks without treatment. Those with a better chance of recovery include those with hearing loss at low frequencies and less severe hearing loss. Patients under 15 years or over 60 years old have been found to have a poorer prognosis, as well as those with concurrent symptoms of vertigo or dizziness.

For patients with an identifiable underlying cause, in addition to oral steroids there may be another therapy required, such as antibiotics to treat bacterial infection or substituting a medication for a less ototoxic drug.

Audiometry testing is valuable not only for diagnosing SSHL but also can provide some information about prognosis and to monitor recovery. A tuning fork test, known as the Rinne test, can help to differentiate sensorineural hearing loss from other types of loss by comparing air conduction to bone conduction in the ear. To rule out other causes of SSHL, the doctor may request MRI scans or various blood tests.

There is some debate surrounding the necessity of treatment as around 50% of idiopathic SSHL cases self-resolve without the need for medical intervention. The current practice guidelines by the American Academy of Otolaryngology – Head and Neck Surgery recommend clinicians educate patients with SSHL about the possibility of spontaneous resolution and the benefits versus risks of medical intervention. Despite this, studies have found the vast majority of clinicians presented with SSHL will opt to treat with steroid medications.

Tinnitus is a commonly presenting symptom alongside SSHL. Unfortunately, even after restoration of hearing loss, tinnitus is known to persist and may, in fact, present as a greater source of distress than the hearing loss itself. Long-term, the usefulness of hearing rehabilitation with hearing aids or cochlear implants should not be underestimated in improving the quality of life for those affected by SSHL and its consequences – it’s always preferable to hear the world in surround sound.

References
Sudden sensorineural hearing loss (SSHL). https://www.healthline.com/health/sensorineural-deafness
Sudden onset hearing loss. https://www.racgp.org.au/afp/2013/september/sudden-onset-hearing-loss/
Sudden sensorineural hearing loss: a review of diagnosis, treatment, and prognosis. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4040829/
Rinne and Weber tests. https://www.healthline.com/health/rinne-and-weber-tests
Clinical practice guideline: sudden hearing loss (update). https://journals.sagepub.com/doi/full/10.1177/0194599819859885