With another wave of COVID-19 infections building and a peak expected around Christmas 2023, the pandemic is now having a double impact on both people with new acute infections as well as on people suffering with a variety of post-COVID-19 conditions.

Among these, there are increasing reports of Sudden Sensorineural Hearing Loss (SSNHL) and other auditory disturbances arising following acute COVID-19 infection.^1-3

SSNHL is the rapid loss of hearing of 30 decibels (dB) or greater over less than 72 hours.⁴ This hearing loss is generally idiopathic (arising spontaneously with no clear cause) and unilateral (affecting only one ear).^5-7 Sensorineural hearing loss is a result of damage to the inner ear, as opposed to conductive hearing loss, which is a result of damage to the middle or outer ear.⁸ SSNHL is often accompanied by a range of comorbid symptoms including a feeling of ear ‘fulness’, vertigo, and tinnitus.⁵ The hearing loss may be present when first waking in the morning,⁹ can develop rapidly during the day,¹⁰ or suddenly appear after hearing a loud ‘pop’.⁵ The global incidence of SSNHL in the general population (i.e., not associated with COVID-19) is 5-27 per 100,000 people, per year.¹¹ SSNHL is typically observed in people between the ages of 50-60, with the least affected group being those aged 20-30.¹²

SSNHL and COVID-19

During the early stages of the COVID-19 pandemic an increased incidence rate of SSNHL presentations was detected at a Turkish hospital, with 41 of 68 (60.3%) patients presenting with SSNHL patients also presenting with recent or current symptoms that suggested a COVID-19 infection.¹³ A similar trend was observed in a Chinese hospital, with a higher incidence rate of patients presenting with tinnitus or sudden deafness during the COVID-19 pandemic as compared to the same period the previous year.¹⁴ These findings, and observations by medical staff across the globe during the peak of the COVID-19 pandemic, brought to light the existence of this unexpected manifestation of COVID-19.

While at this stage, SSNHL following or during acute COVID-19 was poorly understood, the existence of a link was becoming evident. In 2021, Dusan and colleagues found that among 74 COVID-19 patients in Serbia, 30 (40.5%) experienced sensorineural type of hearing loss.¹⁵ Then in 2023, Dorobisz and colleagues found that among a cohort of 58 patients who had PCR-confirmed COVID-19 up to six months prior, 65.5% (n=38) could be diagnosed with sensorineural hearing loss.¹⁶ More modest incidence rates suggest an increase of SSNHL during the COVID-19 pandemic to be around 3.2%, compared to 0.0005%-0.16% before the pandemic, suggesting that COVID-19 may be among the causes of SSNHL.¹⁷ As viral aetiology for SSNHL has been previously observed, the assumption that COVID-19 may cause SSNHL is not solely theoretical.¹⁸

Aetiology

While the causes of SSNHL are often idiopathic,⁶ COVID-19-related SSNHL has been theorised to be a result of the virus affecting the cochlear hair cell functions, ¹⁹ and COVID-19 viral inflammation causing labyrinthitis or vestibular neuritis.^20,21 These theories are supported by evidence of the SARS-CoV-2 virus presence in the porous areas of the mastoid bone suggesting the virus may gain access to the labyrinth compartment,^22,23 and similar aetiology findings of other viral infections causing SSNHL.^21,24 Some studies suggest that SSNHL may be a later developing symptom caused by postinfectious inflammation of the auditory nerve and perineural tissue.^16,25 Further, as COVID-19 is known to be neurotropic, there is potential for it to affect the auditory centre in the temporal lobe,²⁶ resulting in sudden hearing loss.^27,28 More research is needed to understand the aetiology of COVID related SSNHL, however, it is evident that there is potential for auditory COVID-19 manifestations.²⁹

Symptoms

COVID-19 related SSNHL presentations are likely to be comorbid with tinnitus, vertigo, and dizziness, with a small amount of people also experiencing peripheral nerve palsy.³⁰ Additionally, some may experience chemosensory loss prior to hearing loss,^31,32 suggesting that the loss of taste and/or smell could prodrome COVID-19-related SSNHL. Symptoms are likely to develop at between seven days to two moths post COVID-19 diagnostic,^2,17 suggesting that COVID-19 related SSNHL may be a delayed symptom of COVID-19 and occur after the recovery from the acute phase, however some may developed it before the diagnosis of COVID-19.²

Diagnosis

The diagnosis of SSNHL requires ruling out conductive hearing loss.⁹ Sensorineural hearing loss is a result of damage to the inner ear, often to the cochlear hairs, whereas conductive hearing loss is a result of sound waves being unable to reach the inner ear, often a result of damage or blockage to the middle or external ear.⁸ This distinction can be made by using tuning fork evaluations, otoscopy, acumetry, tonal audiometry, speech audiometry, and tympanometry diagnostics, which can also be used to determine the extent of hearing loss.^33,34 Further, a MRI can be performed to help discount specific causes of hearing loss and may help in assessing the hearing losses aetiology.^34,35 If the cause of hearing loss remains unknown, practitioners are urged to consider the possibility of the link between SSNHL and COVID-19 and begin an immediate course of treatment.

Treatment

Early detection and aggressive treatment of SSNHL is required for best outcomes and to reduce risk of permanent damage.^36,37 Treatments for COVID-19 SSNHL are suggested to include an immediate course of systemic steroids (e.g., Corticosteroids, Glucocorticoids).³⁶ A high-dose of oral steroids, ³⁸ intratympanic treatment, ² or a combination of the two is recommended.⁹ The immediate use of systemic steroids may help to reduce viral inflammation in the inner ear,³⁹ however as they are immunosuppressant risks and benefits for patients on high-dose steroids should be considered,⁴⁰ especially for those with current COVID-19 infections.⁴¹ Treatment is most effective when prescribed within two weeks,⁴² therefore those with suspected SSNHL are urged to seek immediate medical attention.

Conclusion

Preliminary findings on the causes of SSNHL following acute COVID-19 findings suggest a neurotropic pathophysiology,^27,28 with a prevalence rate of around 3.2% following acute COVID-19.¹⁷ SSNHL often presents in previous COVID-19 sufferers as sudden, mild, unilateral hearing loss, often alongside of tinnitus and vertigo. Those with any symptoms are urged to seek immediate medical attention as aggressive courses of steroids are required for best outcomes. Additionally, clinicians should consider the COVID-19 may lead to SSNHL and conduct screening where appropriate, to allow for early diagnostic and treatment.³⁸

Clinicians and policy makers should recognise SSNHL as a possible sign of COVID-19, a complication of acute COVID-19 and Long COVID. Additionally, research supported via the Medical Research Future Fund (MRFF) into post-acute sequelae of COVID-19 (PASC) should include a focus on COVID-19-related SSNHL, its aetiology and its impact on sufferers. With the growing number of COVID-19 cases in Australia, up to date COVID-19 vaccinations remain recommended for reducing the risk and severity of COVID-19 infection, and no large-scale clinical evidence exists to suggest that the vaccination may impact upon the prevalence of SSNHL following COVID-19.⁴³

References

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Authors:

Jarrod Clarke and Dr Micah DJ Peters are also based in the Rosemary Bryant AO Research Centre, Clinical and Health Sciences, University of South Australia. Jarrod and Micah are also from the Australian Nursing and Midwifery Federation’s (ANMF) National Policy Research Unit (Federal Office). Micah holds adjunct appointments at the University of Adelaide with Health Evidence Synthesis, Recommendations and Impact (HESRI) in the School of Public Health and the School of Nursing, Health and Medical Sciences.

Kim Gibson is a registered nurse and lecturer based in the Rosemary Bryant AO Research Centre, Clinical and Health Sciences, University of South Australia.