Sudden Hearing Loss

What is Sudden Sensorineural Hearing Loss?

SSNHL is a rapid and unexplained loss of hearing that occurs in the inner ear. The clinical definition includes:

• A hearing loss of at least 30 decibels (dB)
• Affecting at least three consecutive frequencies on a hearing test
• Occurring within a 72-hour period

To better understand this, imagine suddenly losing the ability to hear your friend's voice clearly during a conversation, or struggling to hear the TV at your usual volume setting. This sudden change can be quite alarming and disorienting for patients.

How Common is SSNHL?

While SSNHL isn't an everyday occurrence, it's more common than many people realize:

• Annual incidence (based on US data): 5-20 cases per 100,000 people per year
• At least 2,000 new cases in Canada each year (extrapolating from US data)
• Most common in adults aged 50-60
• Affects men and women equally
• Can occur at any age, but rare in children

It's important to note that these numbers might be underestimated because some cases go unreported or are misdiagnosed as other conditions.

What Causes SSNHL?

The exact cause of SSNHL remains a subject of ongoing research.

In 90% of individuals, we find no cause for the SSNHL. In those situations, it is considered "idiopathic". The main theories explaining "idiopathic" SSNHL include:

1. Circulatory Disturbance:
   • This theory suggests that a reduction in blood flow to the cochlea (the hearing organ in the inner ear) could lead to SSNHL.
   • Possible causes include blood clots, narrowed blood vessels, or sudden drops in blood pressure.
   • Ultimately, this leads to lack of blood supply and cell death in the inner ear along with hearing loss.
2. Viral Infection:
   • Viruses like herpes simplex, cytomegalovirus, or influenza might infect the inner ear or the hearing nerve.
   • These infections ultimately results in inflammation in the inner ear and direct damage to the hearing structures.

In only 10% of individuals, we can find an underlying cause. The common ones would be:

1. Acoustic neuroma (or vestibular schwannoma): This is a benign tumor of the hearing and balance nerves. The tumor will irritate the hearing nerve of the cochlear itself, causing SSNHL. If you suffer from a SSSHL, the chances of it being caused by a vestibular schwannoma is less than 5%. However, in someone with a known vestibular schwannoma, the risk of having a SSNHL episode can be as high as 20-25%!
   
   
2. Autoimmune reaction: SSNHL can be sign of autoimmune diseases such as sarcoidosis, Wegener's disease, lupus, etc. Typically, these patients will have recurrent episodes of SSNHL, or even bilateral episodes of hearing fluctuations.
   
   
3. Cochlear hydrops: This is a disorder in which there is elevated pressure in the inner ear. When the pressure becomes too high, hearing can drop suddenly. This usually affects the low frequencies and can also be recurrent unlike SSNHL.
   
   
4. Perilymphatic fistula: This is caused by a breach in the inner ear membranes causing an abnormal communication between the inner and middle ear. This leads to the inner ear fluid (the perilymph) to escape, causing episodes of fluctuating hearing loss and vertigo. Usually associated with head trauma or surgery to the ear.

COVID-19 and SSNHL: Is There a Link?

There is growing scientific proof suggesting a potential link between COVID-19 and sudden sensorineural hearing loss (SSNHL). Several studies have reported cases of SSNHL occurring during or after COVID-19 infection, even in patients with mild symptoms (1). A systematic review found that approximately one-third of patients presenting with SSNHL during 2020-2021 were positive for COVID-19 (2).

Additionally, a major study in South Korea found that young adults who recovered from COVID-19 had a 3.44 times higher risk of hearing loss and a 3.52 times higher risk of sudden sensorineural hearing loss compared to those who never had COVID-19 (3). The authors of the study suggest that it may be due to direct damage to cochlear structures from the virus, inflammatory responses in the inner ear, inflammation of blood vessels in the inner ear causing small clots, and potential spread of viral meningitis to the inner ear.

However, it's important to note that while these associations have been observed, a definitive causal link has not yet been established, and more research is needed to fully understand the relationship between COVID-19 and SSNHL. You can read more about the link between COVID-19 and hearing loss in this article.

Clinical Presentation of Sudden Hearing Loss

The typical presentation is that of a rapid and "sudden" hearing loss. Patients often describe the onset as dramatic, like a "pop" in the ear followed by muffled hearing. The hearing loss affects one ear in over 95% of SSNHL. Patients usually suffered from a recent viral infection (a cold for instance), although this is not always the case.

Sometimes, however, the change is not as dramatic. Patients feel like they hear less well, but will attribute it to a wax plug or fluid buildup. They may see their local pharmacy for an ear cleaning, and not seek medical evaluation. They may try nasal sprays to unblock the ear. This can lead to delays in the diagnosis and may result in missing the critical period for treating the hearing loss effectively.

If you suspect you may suffer from sudden hearing loss, do not wait and seek urgent medical attention with your ENT, your audiologist or even the emergency room.

Other symptoms typically include:

• A feeling of fullness or pressure in the affected ear
• Tinnitus (ringing, buzzing, or hissing in the ear)
• Dizziness or vertigo in about 30-40% of cases
• Difficulty understanding speech, especially in noisy environments
• Sometimes accompanied by ear pain, but this is less common

Risk Factors for SSNHL

While SSNHL can affect anyone, certain factors may increase the risk:

• Age: Most common in people in their 50s and 60s
• Cardiovascular risk factors: High blood pressure, high cholesterol, diabetes
• Recent upper respiratory infection
• Exposure to loud noises
• Stress
• Smoking
• Excessive alcohol consumption
• Family history of hearing loss
• Certain autoimmune diseases

Medical Evaluation and Work-up

A thorough evaluation is crucial for proper diagnosis and treatment of SSNHL:

1. Detailed Medical History:
   • Onset and progression of symptoms
   • Recent illnesses or medications
   • History of noise exposure, head trauma or autoimmune disorders 
   • Family history of hearing loss
   • Other associated symptoms: dizziness, neurological symptoms, etc.
     
     
2. Physical Examination:
   • Otoscopy to examine the ear canal and eardrum and rule out an infection or fluid build up behind the ear.
   • Neurological exam to check for signs of central nervous system involvement
     
     
3. Comprehensive Hearing Test (Audiogram):
   • The single most important test to obtain urgently.
   • Pure tone audiometry to measure hearing thresholds
   • Speech audiometry to assess speech understanding
   • Tympanometry to evaluate middle ear function
   
   
4. MRI of the internal auditory canal (MRI IAC):
   • To rule out tumors or other structural abnormalities of the brain, hearing nerves and cochlea
   • This does not need to be done urgently as it does not affect the care in the acute setting (the treatment will not change).
     

Prognostic Factors (Factors Affecting Outcomes)

Several factors can influence the likelihood of recovery from SSNHL:

• Severity of initial hearing loss: Milder hearing loss tends to have a better prognosis
• Age: Younger patients generally have better recovery rates
• Presence of vertigo: May indicate more extensive damage and poorer prognosis
• Shape of the audiogram: Certain patterns (like low-frequency or mid-frequency hearing loss) may have better outcomes
• Time between onset and treatment: Earlier treatment is associated with better outcomes
• Overall health: Patients with fewer comorbidities (especially cardiovascular diseases) tend to have better recovery

Treatment Options

Treatment for SSNHL aims to recover as much hearing as possible by reversing the inflammation that happened in the inner ear. The main options include:

1. Oral Corticosteroids (prednisone):

• Usually the first-line treatment
• Typically prescribed for 10-14 days
• Work by reducing inflammation and swelling in the inner ear
• ONLY recommended within the first 2 weeks of the onset of the hearing loss. If more than 2 weeks have passed, oral prednisone is no longer recommended, and instead intra-tympanic injections would be used.
  
  
• In the first 2 weeks, some clinicians (including myself) will combine oral prednisone + intratympanic prednisone for people that suffer from severe to profound SSNHL. There are some studies showing that combining both therapies improves the chances of recovery in that group of patients (4).

2. Intratympanic Corticosteroid Injections:

• Involves injecting steroids directly into the middle ear via a long but thin needle
• Can be used as:
  • Initial treatment (if a patient cannot take oral prednisone, or when combined to oral prednisone) or as
  • "Salvage" therapy if oral steroids didn't work or if more than 2 weeks have passed since the onset of the hearing loss 
• May have fewer systemic side effects than oral steroids
  
• Usually a total of 3-4 doses will be administered, at a frequency of one or two times a week
• Can only be administered up to 6 weeks after the onset of hearing loss. If more than 6 weeks have passed, intra-tympanic prednisone would no longer be recommended.
  

3. Hyperbaric Oxygen Therapy 

• Involves breathing pure oxygen in a pressurized room
• May improve oxygen supply to the inner ear
• Can be used as: initial treatment or as "salvage" therapy (up to 1 month after the onset of symptoms), but always used in combination with steroid treatment
• Its effectiveness remains a topic of debate.
  
  

❗❗❗ No further treatment can be given if more than 6 weeks have passed since the onset of the hearing loss. This is why rapid diagnosis and treatment is critical in SSNHL.

 

According to the 2019 American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) clinical practice guidelines:

• Oral corticosteroids are strongly recommended as initial therapy for SSNHL
• Intratympanic corticosteroid therapy is recommended as initial therapy for patients who can't tolerate oral steroids, or as salvage therapy for patients who don't respond to oral steroids
• Hyperbaric oxygen therapy may be offered within 2 weeks of onset of SSNHL or up to 1 month as salvage therapy.
• The guidelines recommend against routine use of antivirals, thrombolytics, vasodilators, or vasoactive substances
• Follow-up audiometric evaluation is recommended within 6 months of diagnosis

How To Live With Single-Sided Deafness 

If you suffered from a severe episode of SSNHL, and treatment was unsuccessful in restoring your hearing in that ear, you will only have one residual ear to function. This is a situation we call "single-sided deafness" (also called SSD).

Living with single-sided deafness can be challenging, as it affects not only hearing but also daily interactions and overall quality of life. People with single-sided deafness often struggle with sound localization, making it difficult to determine where sounds are coming from, such as a ringing phone or approaching vehicles. Background noise in social settings can make conversations exhausting, as the brain has to work harder to focus on a single voice without the benefit of binaural hearing. This can lead to feelings of frustration, fatigue, and even social isolation. Additionally, individuals may feel vulnerable in certain situations, such as crossing streets or responding to people speaking on their deaf side.

Hearing rehabilitation strategies for single-sided deafness

The aim is to improve sound awareness and communication. Common options include :

1. Contralateral routing of signal (CROS) devices: Type of hearing aids that transfer sound from the deaf side to the better-hearing ear. Simply put, while you won't regain hearing in the deaf ear, the CROS hearing aid will pick up sounds from that side and transmit them to your better-hearing ear. This allows you to hear sounds from that direction without needing to constantly turn your head. You will need a hearing aid in each ear for this to work (one captures the sound, the other one emits the sound).
   
   
2. Bone conduction devices (such as BAHA, Ponto, etc.), which are surgically implanted devices that transmit sound vibrations through the skull to the functioning ear.

   It operates on the same principle as the CROS hearing aid, which is to transmit sounds from the deaf ear to the functioning ear. However, instead of utilizing two hearing aids, the implanted device conveys sound to the good ear through skull vibrations. The primary benefits include improved sound clarity and the elimination of the need for any hearing aid.

3. Cochlear implant (CI): While CROS hearing aids and BAHA devices improve sound awareness, they cannot restore true binaural (with both ears) hearing. For those seeking more advanced solutions, cochlear implants are the only option that can restore binaural hearing by directly stimulating the auditory nerve on the deaf side. In most places, it is hard to get approved for a CI when you suffer from single-sided deafness, because you have one functioning ear (CIs are usually done in patients with bilateral deafness). 

There are in addition rehabilitation strategies that involves practical changes like sitting with the deaf ear against a wall in noisy environments and being open with others about the condition to foster understanding and support. With a combination of technology and adaptive techniques, individuals with SSD can significantly enhance their quality of life.

Conclusion

It's crucial to start treatment as soon as possible after the onset of symptoms. ENTs consider SSNHL a medical emergency, and earlier treatment is associated with better outcomes. Remember, if you or someone you know experiences sudden hearing loss, seek medical attention immediately. Don't wait to see if it gets better on its own – prompt treatment can make a significant difference in recovery.