Hearing Loss: An Odd Covid-19 Symptom We Overlooked
It appears suddenly in young people without any prior hearing problems [updated Sept].
A study published in the American Journal of Otolaryngology on 2nd April reported the first case of hearing loss in Covid-19. Among the 82 cases of Covid-19 in Thailand, an old female developed hearing loss. Her respiratory symptoms recovered, but hearing loss persisted, they found. “Probably, a neuro-auditory problem developed in the patient,” a research group in Turkey commented on the Thailand report. “Hearing loss in COVID-19 infection has never been reported in the literature so far.”
More Cases of Covid-19 Hearing Loss
A week later, another study on 20 Covid-19 symptomless cases found their hearing abilities worsened, based on multiple auditory tests, compared to controls. Patients were 20–50 years old and had no prior medical history of hearing problems. “The results of the current study showed that Covid-19 infection had deleterious effects on the hair cells in the cochlea,” the Egypt study concluded. “Moreover, the absence of the major symptoms does not guarantee a safe, healthy cochlear function.”
Cochlear is a spiral-shaped bone (purple in the figure) located in the inner ear. It is responsible for the sense of hearing and conversion of sound waves into neural signals interpretable by the brain.
Later in June, a study in Iran examined six Covid-19 patients aged 22–40 years with mild clinical symptoms of cough, fever, and breathing difficulties. They had no relevant records of medical or hearing concerns. Yet, after contracting Covid-19, their hearing suffered. Four had tinnitus (noise or ringing in ears), two had vertigo (hearing-related loss of balance), and all had mild-to-moderate hearing loss in one ear.
“It is highly likely that these otologic symptoms are directly related to/caused by Covid-19,” the Iran otolaryngologist closed. They further claimed that they had seen many patients — without prior hearing problems — who suddenly had difficulties hearing or balancing in recent weeks before they conducted their study.
[24th July update] An autopsy study published in JAMA Otolaryngology-Head & Neck Surgery has detected SARS-CoV-2 genetic material in the middle ear and mastoid (an ear bone containing air cells that surround the inner and middle ear) of two out of three deceased Covid-19 patients. “This study confirms the presence of SARS-CoV-2 virus in the middle ear and mastoid, with significant implications for otolaryngology procedures,” the study authors at the Johns Hopkins School of Medicine concluded.
[4th September update] A new study appearing in the European Archives of Oto-Rhino-Laryngology journal documented the symptoms of 155 Covid-19 patients (mean age of 36) admitted to a hospital in Turkey. The study found that only four patients (2%) had ear pain, two (1.2%) had tinnitus, and one (0.6%) had hearing loss. This research shows that hearing problems may not be so common in Covid-19 after all.
Putting Into Context
Former coronaviruses such as SARS-CoV-1 and MERS-CoV do not impair hearing, at least there are no reported cases. However, virus-induced hearing or balance loss is a familiar phenomenon. “Normally [viruses] cause all the symptoms you know well, but sometimes, for whatever reason, they get into the inner ear and wreak havoc there resulting in sudden hearing loss and/or balance problems,” stated Dr. Neil G Bauman, a CEO at The Center for Hearing Loss Help in Washington. Some examples are:
- Herpes simplex virus type 1 (HSV-1) DNA can be found in vestibular nerves of the inner ear of infected patients with vertigo (i.e., loss of balance). HSV-1 can also cause hearing loss in 56% of infected children.
- Herpes zoster virus that causes shingles can also cause Ramsay Hunt Syndrome — facial paralysis and hearing loss — if the virus infects facial nerves near the ear.
- Congenital cytomegalovirus infection causes about 25% of cases of hearing deficits in infants and children.
- Measles virus RNA can be found in the middle ear of infected people with otosclerosis — i.e., abnormal growth of middle ear bone leading to severe hearing loss.
- Human immunodeficiency virus (HIV) disrupts auditory functions in up to one-third of patients. Common auditory symptoms of HIV are ear fullness, dizziness, hearing loss, and tinnitus.
Based on the abovementioned studies, hearing loss can happen in mild or symptomless cases of Covid-19. Researchers speculate that SARS-CoV-2 neuroinvasiveness may also target auditory centers in the brain, such as the temporal lobe or brainstem. Autopsies have found SARS-CoV-2 particles in the brainstem. And brain imaging studies [references a, b, c, d] have documented neuronal damage in the temporal lobe and brainstem of Covid-19 patients.
The hearing loss appeared suddenly, often in young people without any prior hearing issues. At least the hearing impairment is mild-to-moderate — and not severe or deaf — which is consistent with other viruses.
Whether the hearing loss in Covid-19 persists for an extended period await further studies to confirm. If the trend also follows other viruses, then the Covid-19 hearing loss should not be permanent. “Most cases of sudden hearing loss are viral, and most patients are treated with steroids,” New York otolaryngologists at Icahn School of Medicine at Mount Sinai explained. “Patients with mild degrees of hearing loss usually recover.”
A Side Effect from Drugs
In a July review titled “Don’t forget ototoxicity during the SARS-CoV-2 (Covid-19) pandemic,” audiologists at the University Hospital of Ferrara pointed out that many drugs used to treat Covid-19 has ototoxicity as a side effect. (Oto- means ear, so ototoxicity means toxicity to the ear.)
These drugs include azithromycin, remdesivir, favipiravir, and lopinavir — all of which have been documented in the literature to cause hearing loss and tinnitus. The ototoxicity severity of these drugs depends on the dose and duration and may appear weeks or months after administration, the review authors said.
Besides, the review also mentioned virus invasion or virus-induced hypoxia (i.e., not enough oxygen in the blood circulation) as possible causes of hearing loss in Covid-19. “It is necessary to consider that SARS-CoV-2 could potentially target directly the inner ear, as many other viruses, that is, HSV and VZV [Varicella zoster virus],” the authors stated. “Furthermore, cochlear hair cells have high metabolic activity and are particularly vulnerable to hypoxic or ischemic damage.”