The Emerging Link Between COVID-19 and Hearing Loss
The COVID-19 pandemic has brought to light various long-term medical conditions that can arise as a result of the infection. These include chronic fatigue, heart damage, lung damage, and psychological disorders. However, emerging research is now investigating another potential impact of COVID-19 on individuals-its potential connection to hearing loss and tinnitus. Understanding this potential relationship is crucial for providing comprehensive care and support to those affected by the virus.
Viral-Induced Hearing Loss: Established Associations
Numerous viruses have been identified as potential causes of Sensorineural Hearing Loss. Among them are mumps, measles, meningitis, and cytomegalovirus. These viruses have been extensively studied, and their association with hearing impairment is well-documented.
The mechanisms by which these viruses lead to Sensorineural Hearing Loss vary. Some viruses directly infect the structures of the inner ear, causing inflammation and damage to the sensory cells responsible for hearing. Others induce an immune response that mistakenly targets the auditory system, resulting in damage to the cochlea or auditory nerve.
Given the established link between these viruses and Sensorineural Hearing Loss, it is reasonable to explore whether a SARS-CoV-2 infection could have similar effects on hearing. While the specific mechanisms of COVID-19-related hearing loss are still being investigated, there is growing evidence suggesting a potential association.
The prognosis for patients with SSNHL varies, with some individuals experiencing spontaneous recovery of their hearing, while others may have persistent hearing loss. Factors such as the severity of hearing loss, age, and underlying cause can influence the prognosis.
Possible Mechanisms Linking COVID-19 to Hearing Loss
Possible routes for the virus to enter the ears include the Eustachian tube, which connects the nose to the middle ear. The virus may also be able to escape from the nose through small openings surrounding the olfactory nerves, Stankovic says.
A new study from MIT and Massachusetts Eye and Ear provides evidence that the virus can indeed infect cells of the inner ear, including hair cells, which are critical for both hearing and balance. The researchers used novel cellular models of the human inner ear that they developed, as well as hard-to-obtain adult human inner ear tissue, for their studies.
In both the human inner ear samples and the stem-cell-derived cellular models, the researchers found that certain types of cells - hair cells and Schwann cells - express the proteins that are needed for the SARS-CoV-2 virus to enter the cells. The researchers then showed that the virus can actually infect the inner ear, specifically the hair cells and, to a lesser degree, Schwann cells.
The human hair cells that the researchers studied were vestibular hair cells, which are involved in sensing head motion and maintaining balance. Cochlear hair cells, which are involved in hearing, are much harder to obtain or generate in a cellular model.
| Cell Type | Role | Susceptibility to SARS-CoV-2 |
|---|---|---|
| Hair Cells | Hearing and Balance | Infected by SARS-CoV-2 |
| Schwann Cells | Support nerve cells | Infected to a lesser degree |
The pattern of infection that the researchers found in their tissue samples appears to correspond to the symptoms observed in a group of 10 Covid-19 patients who reported ear-related symptoms following their infection. Damage to cochlear hair cells, which can cause hearing loss, is usually evaluated by measuring otoacoustic emissions - sounds given off by sensory hair cells as they respond to auditory stimulation.
Link with Guillain-Barre Syndrome
Guillain-Barre syndrome (gee-YAH-buh-RAY), also known as GBS, is a rare neurological disorder that has been associated with auditory neuropathy, a condition characterised by disrupted nerve impulses between the inner ear and the brain, leading to sudden hearing loss.
GBS typically occurs after an infection, often a viral infection. It is believed that the immune response triggered by the viral infection mistakenly attacks the peripheral nerves, including those involved in hearing.
Several coronaviruses have been associated with cases of GBS, including the severe acute respiratory syndrome coronavirus (SARS-CoV) and the Middle East respiratory syndrome coronavirus (MERS-CoV). Given the similarities between these coronaviruses and SARS-CoV-2, the virus responsible for COVID-19, it raises the possibility of COVID-19-related auditory neuropathy. Further research is needed to determine the extent and nature of this potential association.
Understanding the potential links between COVID-19 and viral-induced hearing loss is crucial for healthcare professionals in providing comprehensive care to individuals affected by the virus. By recognising the potential impact on hearing and addressing it promptly, healthcare providers can ensure appropriate management and support for patients experiencing loss of hearing or related symptoms.
Atypical Symptoms of Covid 19
While respiratory symptoms are commonly associated with COVID-19, there is growing evidence suggesting that the virus can also cause atypical symptoms, including acute hearing loss. Some individuals with COVID-19 have reported experiencing changes in their hearing, such as a decline in hearing ability or the onset of tinnitus. These atypical symptoms highlight the need to consider the potential impact of the virus on the auditory system.
Audiovestibular Symptoms
In addition to hearing loss, individuals with COVID-19 may experience audiovestibular symptoms. These symptoms can include dizziness, vertigo, imbalance, and difficulties with spatial orientation. The audiovestibular system, which is responsible for both hearing and balance, can be affected by the virus, leading to these symptoms. Proper evaluation and management of audiovestibular symptoms are essential to minimise their impact on an individual's daily life.
Neurological Symptoms
COVID-19 is known to affect the central nervous system, and neurological symptoms can manifest in some individuals. These symptoms may include headache, confusion, altered consciousness, and nerve-related issues. Since hearing involves the transmission of signals from the ear to the brain, it is possible that the virus's impact on the central nervous system may contribute to hearing-related complications. Further research is needed to understand the neurological mechanisms underlying COVID-19-related hearing loss.
COVID-19 may lead to various degrees of hearing loss, ranging from mild to profound. Some individuals may experience a temporary decline in their hearing ability, while others may face irreversible hearing loss post-infection. The severity of hearing loss can vary depending on factors such as the individual's overall health, age, and underlying conditions. It is crucial to assess the degree of hearing loss accurately to determine appropriate management strategies and support for affected individuals.
“Having the models is the first step, and this work opens a path now for working with not only SARS-CoV-2 but also other viruses that affect hearing,” says Lee Gehrke, the Hermann L.F. Konstantina Stankovic, a former associate professor at Harvard Medical School and former chief of otology and neurotology at Massachusetts Eye and Ear, who is now the Bertarelli Foundation Professor and chair of the Department of Otolaryngology - Head and Neck Surgery at Stanford University School of Medicine, co-led the study. Before the Covid-19 pandemic began, Gehrke and Stankovic began working together on a project to develop cellular models to study infections of the human inner ear. In early 2020, after the SARS-CoV-2 virus emerged, the researchers altered their plans. At Massachusetts Eye and Ear, Stankovic started to see patients who were experiencing hearing loss, tinnitus, and dizziness, who had tested positive for Covid-19. She and Gehrke decided to use the model system they were working on to study infection of SARS-CoV-2.
They created their cellular models by taking human skin cells and transforming them into induced pluripotent stem cells. These cells could be grown in a flat, two-dimensional layer or organized into three-dimensional organoids.
Otoacoustic Emissions
Otoacoustic emissions (OAEs) are sounds that are generated by the inner ear in response to external stimuli. They provide valuable information about the health of the auditory system. Studies have shown that individuals with COVID-19 may exhibit alterations in OAEs, suggesting potential damage to the sensory cells in the inner ear. Monitoring OAEs in individuals with COVID-19 can aid in the early detection of hearing-related complications and guide appropriate interventions.
Study on Hearing Changes in COVID-19 Patients
A previous study conducted at Wythenshawe Hospital in England sought to shed light on the potential impact of COVID-19 on hearing. The study included 121 adults who had been diagnosed with COVID-19 and required intensive care at Wythenshawe Hospital. The participants were carefully selected based on the severity of their symptoms during the COVID-19 infection.
After an eight-week period following their discharge, the participants were questioned about any changes in their hearing or the presence of tinnitus. The results revealed that approximately 13% of the individuals self-reported experiencing hearing deterioration or the onset of tinnitus since their COVID-19 diagnosis. Specifically, eight participants reported a decline in their hearing ability, while an additional eight participants reported the presence of tinnitus.
While these findings provide valuable insights into the potential association between COVID-19 and hearing changes, it is essential to exercise caution when interpreting the data. Several factors other than the virus itself may contribute to these reported hearing changes.
The use of face masks during the COVID-19 pandemic can create communication difficulties and affect how individuals perceive sounds. The hospital environment and associated stressors may also play a role in the reported hearing alterations. Additionally, medications used to treat COVID-19, such as antiviral drugs or other systemic medications, may have side effects that affect hearing.
Implications and the Need for Further Research
Recognising the potential long-term impact of COVID-19 on hearing, it is crucial to conduct high-quality studies to thoroughly investigate the relationship between the virus and hearing loss/tinnitus. Addressing confounding factors such as face mask use, hospital environment, anxiety, and medications is essential in understanding the true impact of COVID-19 on auditory function. Further research is needed to establish a clearer understanding of the connection and provide evidence-based guidelines for prevention, diagnosis, and treatment.
“Initially this was because routine testing was not readily available for patients who were diagnosed with Covid, and also, when patients were having more life-threatening complications, they weren’t paying much attention to whether their hearing was reduced or whether they had tinnitus,” Stankovic says.
Future Directions and Updates
As we continue to navigate the aftermath of the COVID-19 pandemic, it is essential to recognise the importance of ongoing research in the field of COVID-19 and its potential impact on hearing. At Abi Hearing, we are staying updated on new findings and advancements in research, which we believe is crucial for healthcare professionals, audiologists, and individuals themselves. As new studies emerge and data is collected, it is important to stay informed about the latest insights and developments in the field of COVID-19 and hearing loss. This knowledge will guide healthcare providers in providing appropriate care and support to individuals experiencing changes in their hearing.