A novel infectious disease, 2019 Coronavirus disease (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is a highly transmissible and pathogenic human coronavirus (1). Scientific and clinical evidence suggested that COVID-19 can affect multiple organ systems (2). SARS-CoV-2 can also invade the central and peripheral nervous system to cause various neurological diseases (3).

Sudden sensorineural hearing loss (SSNHL) is defined as the sudden onset of sensorineural hearing loss (SNHL) without an identifiable etiology, with at least three consecutive frequency losses ≥ 30 dB within 72 h (4). The annual incidence of SSNHL varies between 5 and 27 cases per 100,000 persons (5). The cause of SSNHL is unclear. However, the possible causes include viral infection, circulatory abnormalities, autoimmune disease, labyrinthine membrane rupture, and central nervous system (CNS) anomalies (5, 6).

Strong evidence suggests that viral infection is a cause of SSNHL (7). It may be related to direct viral access to the labyrinth or the cochlear nerve, reactivation of latent virus inside spiral ganglia, and immunoregulation of systemic viral infections (7). Lassa fever, mumps, adenovirus, and other viruses have caused SSNHL (8–10). Growing data indicate that patients with COVID-19 are prone to SSNHL (7, 11–13). However, many aspects of COVID-19-related SSNHL have remained unclear.

The purpose of this review was to evaluate the impact of COVID-19 on the incidence of SSNHL and to provide an understanding of the clinical characteristics of COVID-19-related SSNHL.

A systematic review was conducted based on the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines (14). Ethics committee approval was not required for this literature review.

This systematic review examined whether COVID-19 leads to an increased incidence of SSNHL by using the available literature. However, the COVID-19 pandemic varied across countries, and the findings were inconsistent and even contradictory. Therefore, it remains unknown whether COVID-19 contributes to the high incidence of SSNHL.

All 23 patients with COVID-19-related SSNHL, included in this systematic review, were adults, with no significant differences in the number of incidences by age group. Pediatric SSNHL is uncommon, and there have been no reports of COVID-19-related SSNHL in children (36). Tinnitus, one of the most common sensorineural disorders, is associated with SSNHL in 66–93% of cases (37). In this review, we found that 60.9% of patients with COVID-19-related SSNHL had tinnitus symptoms similar to the presentation of regular SSNHL.

COVID-19-related SSNHL can occur on one or both sides; however, it is more common on one side (11, 15). Bilateral SSNHL is relatively uncommon (7). However, the likelihood of binaural morbidity in SSNHL was significantly higher in COVID-19 patients than in the general population. Shah et al. studied 4 COVID-19-related SSNHL patients referred to their otolaryngology clinic, 3 of whom presented with bilateral symptoms (13). It may relate to the fact that ototoxicity symmetrically affects both ears (12).

Early audiological assessments and monitoring are critical when suspected or detected with sensorineural hearing loss (SNHL) (38). PTA, otoacoustic emissions, and ABR can all be used to assess the circumstances of patients with COVID-19-related SSNHL (15). PTA helps determine the type and severity of HL. In the era of COVID-19, telemedicine can reduce outpatient follow-up visits, reduce the risk of cross-infection, and improve patient satisfaction (39). According to physical distance requirements and Centers for Disease Control and Prevention guidelines, conventional hearing services are at moderate to high risk for COVID-19 infection (40). As a result, traditional auditory service deliveries are highly restricted. In this context, tele-audiometry has become a workable option for audiometric examination, with a high level of accuracy that is not significantly different from traditional audiometric testing (41). A study by Shilo et al. based on smartphone vibration and uHear App hearing tests also confirmed that the telemedicine model for diagnosing SSNHL is valid and reliable (42). In addition, some improvements can be made to the hearing test technologies to minimize contact with the patient. A recent study has shown that PTA combined with the digits-in-noise test, without bone-conduction thresholds, can distinguish between SNHL and conductive HL (40). Since this hearing test method does not require traditional bone-conduction audiometry in a closed sound booth, it is valuable in preventing cross-contamination.

According to the clinical practice guidelines of the American Academy of Otolaryngology-Head and Neck Surgery, glucocorticoids can be used as initial treatment for SSNHL patients within 2 weeks after the onset of the disease (4). Since there are contradictory results on adverse reactions to corticosteroids in patients with COVID-19, IT administration is a beneficial option (6). A clinical study compared the therapeutic efficacy of IT corticosteroid administration vs. intravenous corticosteroids in COVID-19-related SSNHL, and found comparable efficacy of both treatments (43). However, IT administration did not cause systemic side effects compared to intravenous corticosteroids (43). Therefore, patients with COVID-19-related SSNHL can be treated with IT corticosteroids as soon as they are diagnosed (6).

A recent systematic review and meta-analysis published in JAMA Otolaryngology-Head and Neck Surgery showed, including over 20 years of literature data, that HBOT as part of a comprehensive treatment for patients with SSNHL significantly improves hearing outcomes (44). However, HBOT sessions should be adjusted to meet COVID-19 prevention and control requirements for infection identification, distancing, and isolation, to avoid breathing with an internal chamber atmosphere (45). Moreover, pediatric patients can be safely treated with HBOT (46). Thus, HBOT can be applied while meeting the protection of medical staff and patients to improve the outcomes.

Patients who do not regain their hearing after active treatment may consider hearing aids or CI to improve their hearing. In patients with poor physical condition, CI procedures can be conducted under local anesthesia with analgesia to limit the risk of anesthesia (12).

Individuals with HL may experience challenges, such as difficulty perceiving speech, leading to communication and social difficulties (47). Surgical face masks and face shields were essential for personal protection during the COVID-19 era. However, this impaired the speech perception in individuals with moderate-to-severe HL (48). The pandemic has exacerbated the situation, worsening patients' mental health, particularly in rural areas (49). As a result, the entire society should pay attention to people with HL by giving practical support in various areas such as socialization, detection, treatment, and rehabilitation.

Otolaryngology is considered a high-risk unit for COVID-19 (50). During the ongoing pandemic, there are many infected individuals with atypical symptoms. Each symptom should be considered for association with COVID-19 (51). Kilic et al. detected one positive patient for SARS-CoV-2 among five male patients with unilateral SSNHL as the only complaint in an outpatient otolaryngology clinic (35). SSNHL may be the first symptom of COVID-19. Therefore, all patients with SSNHL and/or acute vestibular disease should be screened for SARS-CoV-2 infection (17, 52). In addition, patients in the otolaryngology outpatient clinic should receive enough attention to their anxiety and stress levels (53).

The majority of the extant research is based on retrospective studies with limited sample sizes, and large-scale prospective investigations are lacking. As a result, large-scale, multicenter research on the pathophysiology, treatment, and prognosis of COVID-19-related SSNHL should be conducted. In the available literature, pure tone audiometry is mainly used to detect COVID-19-related SSNHL, while speech audiometry is rarely used to examine patients' WRS. Speech audiometry may be considered to evaluate the effect of SARS-CoV-2 on cognitive processes.

SARS-CoV-2 has the potential to cause damage to the audio-vestibular system, resulting in SSNHL. However, the exact mechanisms by which SARS-CoV-2 affects the audio-vestibular system remain unclear. Although numerous investigations have been conducted on COVID-19-related SSNHL, they are fragmented and unsystematic. The true prevalence of SSNHL in COVID-19 patients around the world is unknown. Glucocorticoids are the preferred medication to treat COVID-19-related SSNHL. Hearing testing is recommended when HL is suspected in COVID-19 individuals, and if SSNHL is identified, prompt and vigorous treatment is critical.

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.

XM and JS conceptualized and drafted the manuscript. JW and KZ critically reviewed the literature and extracted data. XM revised the draft manuscript. All authors contributed to the article and approved the submitted version.

This study was funded by the Science and Technology Development Project of the Bureau of Science and Technology of Wuxi, China (Grant number CSZ0N1622).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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