Oral Manifestations of Coronavirus Disease 2019 (COVID-19): An Overview

Chemosensory dysfunction: dysgeusia

One of the most common, well-recognized oral manifestations of COVID-19 is chemosensory dysfunction, leading to alterations of taste (dysgeusia) either with, or without, olfactory involvement (anosmia). There are now several reports and reviews in the literature on dysgeusia that could be characterized as a pathognomonic symptoms of COVID-19.⁴ In a previous COVID-19 commentary, we dealt with this subject in detail,⁵ although further data are now available on the condition, including a metanalysis of 31 reports by Dos Santos et al.⁶ They noted the global prevalence of taste disorders in 45% of COVID-19 patients, with 24% ageusia, 35% hypogeusia, and 38% with dysgeusia. With a moderate certainty of the evidence, they also found that taste disorders are associated with COVID-19 positivity, mild-to-moderate disease severity, and female sex. Some have evaluated the specific loss of different flavours in COVID-19-related dysgeusia, and reported, 77% with changes in their ability to taste spice, 80% for saltiness, 79% for sourness, and 91% for sweetness. However, the veracity of these data are questionable because they were obtained from a web-based questionnaire survey.⁷

The reason/s for the loss of taste in COVID-19 is/are unclear. Some have speculated that the increasing number of ACE-2 receptors on the tongue keratinocytes and the associated cell death and desquamation may block the taste buds and adversely affect taste perception.^8,9 Whether the dysgeusia is due to direct damage to the taste buds located in the filiform, fungiform and vallate papillae by the SARS-CoV-2 virus is unclear as yet. Dysgeusia is almost always temporary, and normal taste sensation returns by 4–6 weeks after recovery from the acute COVID-19 illness. Additionally, some reports indicate that women experience the condition more than men, although confirmatory evidence is required.^10,11

Salivary glands and saliva in COVID-19

One contributory reason for dysgeusia or ageusia could be the reduction in salivary flow or xerostomia associated with COVID-19. Considering that salivary tissues are replete with ACE-2 receptors, which are portals of cellular entry for SARS-CoV-2,¹² it is not surprising that salivary glands are profoundly affected by COVID-19, leading to a reduction in the salivary secretions. Indeed, it is now known that not only the major, but also the minor salivary glands in the labial and other regions of the oral cavity can be infected by SARS-CoV-2.¹²

Other secondary co-factors for COVID-19-induced xerostomia are thought to be impaired nasal breathing due to nasal congestion and/or rhinorrhoea due to the disease, which in turn, may induce a feeling of oral dryness and a sense of xerostomia, either apparent or real.¹³ Pandemic-induced psychosocial factors and chronic stress may also contribute to the functionality of salivary glands and quantitative reduction in salivary secretions.^13,14

Oral mucosal lesions (Table 1)

Reported oral mucosal manifestations associated with COVID-19 are many and varied, as shown in Table 1. Nevertheless, the vast majority of these are single anecdotal reports or mini-case series with a handful of patients, and hence their veracity remains to be confirmed. The lesions reported range from ulcers, erosions, bullae, vesicles, mucosal pustules, macules, papules and pigmentations; fissured or de-papillated tongue; and haemorrhagic manifestations, including petechiae, crusts, and spontaneous bleeding (Figure 1).

In a global review of oral manifestations of COVID-19, Iranmesh et al¹⁷ describe over 30 articles, including case reports, letters to the editor, and case series on oral manifestations. Since their publication, many other reviews have appeared describing similar lesions in COVID-19. However, none of these lesions appears to be specific for the disease, as most are relatively common generalized manifestations of systemic viral infections. For instance, enanthems are common in dengue fever disease, herpangina, human herpes virus infections, measles, and roseola infantum.

In relation to the anatomical site of the described mucosal lesions, the most common sites of presentation appear to be the tongue (38%), followed by the labial mucosa (26%) and the palate (22%). In 68% of the reported cases, oral lesions were symptomatic and almost equal in both genders (51% male and 49% female). Older patients and those with very severe COVID-19 disease had more widespread and more severe oral lesions. The vast majority of oral lesions healed, and appeared to resolve about 4 weeks after their appearance. However, fresh lesions, or crops of lesions, may appear at various stages of the disease, depending on the patient's immune status.

Perspectives

Referral to Table 1 indicates the many and varied oral manifestations of COVID-19 described in the literature thus far. At this stage, without a prospective, standardized audit of these patients, it is difficult to state with certainty the most prevalent oral lesions associated with COVID-19, apart from dysgeusia, which is generally accepted as a hallmark of the disease in many. Nevertheless, it is likely that ulcerated lesions such as herpetiform and aphthous-like lesions and white patches resembling candidiasis are more common than the others. Clearly, the presentation and frequency of oral manifestations appear to be higher in older, hospitalized cohorts, with severe COVID-19 due to a multiplicity of factors, such as immune impairment, underlying diseases (eg diabetes mellitus), poor oral hygiene, adverse drug reactions, stress, hyper-inflammatory responses secondary to COVID-19, and iatrogenic trauma (secondary to intubation).

Whether the currently emerging new viral variants will impact the oral manifestations of the disease is another unknown. Highly controlled and standardized, multicentre, prospective studies are required to yield not only definitive data on the subject, but also the optimal interventional procedures to improve the quality of life in these patients.