Q&A: Causal link between COVID-19 and hearing, balance disorders ‘weak’
A growing amount of evidence, albeit limited in its strength, suggests that auditory and vestibular effects should be added to the list of symptoms linked to COVID-19, according to an expert.
Colleen Le Prell, PhD, a professor and chair of the department of speech, language and hearing at the University of Texas at Dallas, said the inflammatory effects of COVID-19 in neurological tissue may be to blame.
“Inflammation can damage the auditory and vestibular pathways in the peripheral and central nervous system, just as it damages smell and taste pathways and other neural systems,” she said in a press release.
Le Prell cautioned that unproven treatments for COVID-19, such as chloroquine and hydroxychloroquine, may also have adverse auditory effects, particularly in patients with kidney problems.
“When the kidneys are not functioning properly, the drug may not [be] metabolized and eliminated from the body as quickly, which can increase physiological drug concentrations and risk of side effects,” Le Prell said in the release. “Old age is often accompanied by decreased renal function, and COVID-19 can cause renal dysfunction, which increases the risk that a patient who is given an experimental therapy for COVID-19 will be at risk for ototoxicity.”
In an interview with Healio Primary Care, she discussed the limitations of the evidence surrounding the link between COVID-19 and hearing and balance disorders, the duration of such symptoms, who might be more susceptible to these effects and more.
Healio Primary Care: What evidence is there to suggest that hearing and balance disorders are symptoms of COVID-19? How strong is the evidence?
Le Prell: Most of the evidence that hearing and balance disorders are symptoms of COVID‐19 comes from case reports and retrospective reviews using patient databases. Thus, much of the data is descriptive in nature, providing statistical information about the percent of patients hospitalized with COVID-19 who also have documentation of specific symptoms such as hearing loss, tinnitus or balance disorders. Some studies specify new hearing loss, tinnitus or balance disorders, but some studies might identify people with preexisting symptoms if their methodology is not limited to new symptoms. These studies also generally have not included any control population to look at the prevalence of symptoms in age‐ or otherwise-matched individuals who have not tested positive for COVID‐19. Thus, the evidence for causal relationships is relatively weak, suggesting but not confirming possible relationships.
Healio Primary Care: About how long do hearing and balance disorders related to COVID‐19 last?
Le Prell: I am not aware of any data regarding the duration of hearing and balance disorders after COVID‐19. Depending on the specific pathology that underlies the disorder, recovery may or may not be possible. Many of the cells in the cochlea do not have a regenerative process and if those cells die, they are not replaced by new cell growth.
Healio Primary Care: Does COVID-19 severity impact the likelihood of developing these symptoms?
Le Prell: The majority of the published research is drawn from severe COVID‐19 cases, requiring hospitalization for other severe and possible life‐threatening symptoms. One study looked at individuals who were identified as asymptomatic cases, and the asymptomatic group had poorer hearing outcomes compared to a control group that was specifically recruited as a normal hearing control group. The small observed differences need to be interpreted with caution as it is possible that the experimental group (identified as asymptomatic) could have had hearing loss prior to the COVID‐19 infection. Prospective longitudinal data, in which changes in hearing within the same group of people are monitored, are needed. Those data allow the amount of hearing change over time in those with and without COVID‐19 infection to be determined.
Healio Primary Care: What preexisting conditions might make a person more susceptible to experiencing hearing and balance disorders as a symptom of COVID‐19?
Le Prell: There are not any published data on this. Because COVID 19 attacks many neurological systems throughout the body, one could speculate that preexisting neural damage might increase the risk for hearing and balance disorders, as the loss of additional neurons or other vulnerable cells could more quickly result in measurable deficits. Another possibility that should be considered is the potential for ototoxic side effects of COVID‐19 therapeutics. A number of the drugs being investigated as possible therapeutics have resulted in either temporary or permanent hearing loss when these drugs have been used for other disease conditions. Increased doses used for COVID‐19 patients and the combination of multiple drug treatments within COVID‐19 patients could increase those risks.
Healio Primary Care: What are the possible reasons for the link between these disorders and COVID-19?
Le Prell: COVID‐19 is well documented as causing a cytokine storm — essentially a condition in which the body’s defense mechanisms act against its own tissues. When the immune system is activated, white blood cells release inflammatory cytokines, and these cytokines recruit additional immune cells to the site of injury. In COVID‐19, this process can be increased to the point that it becomes pathological rather than beneficial. This is thought to be the cause of damage to the auditory and vestibular systems, as well as other tissues.
Healio Primary Care: Should PCPs screen for hearing and balance disorders in patients with COVID‐19? When should they refer patients with these symptoms to a specialist?
Le Prell: Even outside of COVID‐19, there has been significant discussion among the public health service agencies, scientists and clinicians regarding the benefits of hearing and balance screenings, including whether early identification leads to early intervention.
If a patient reports difficulty communicating with others in quiet or in noise, has balance deficits that put them at risk for falling and injuring themselves, or has other hearing or balance complaints, referral is certainly warranted so that rehabilitation options can be discussed.
In the absence of symptoms or complaints, there is not consensus across stakeholder groups on routine hearing and/or balance screening. There are tests that are sensitive to preclinical pathology, such as otoacoustic emission tests which provide a measurement of the health of a specific type of sensory cell (the outer hair cell). If decreased emissions are detected during screening, patients can be counseled regarding the need to protect their ears against additional injury, and educated on hearing protection options that best meet their hearing needs. Decreased emissions have been reported in asymptomatic COVID‐19 cases, although the level of evidence is still weak as prospective longitudinal data are lacking.
Acoustical Society of America. COVID-19 creates hearing, balance disorders, aggravates tinnitus symptoms. https://www.eurekalert.org/pub_releases/2021-06/asoa-cch060721.php. Accessed July 22, 2021.