2.8. Nonspecific Lesions (Mucositis)
Petechiae, macules, erythema, stomatitis, brown pigmentation, mucositis, enanthema, and desquamative gingivitis were reported in many hospitalized patients [
26]. Vascular disorders could cause mucositis in the affected patients. Indeed, Cruz-Tapia et al. described a 51-year-old female with diffuse vascular-like purple macule on the left palate and a papule-plaque on the right palate [
68]. Riad et al. described 13 patients affected by mucositis; enanthema of the buccal mucosa, palate, and gingiva; and depapillation of the tongue, at hospitalization. These lesions disappeared after 7–14 days of “Magic mouthwash” and paracetamol and could be related directly to COVID-19 infection [
6,
89]. Only one study described a patient affected by oral lichenoid reaction and a case with oral enanthema, directly due to COVID-19 [
54]. Marouf et al. suggested that periodontitis was significantly associated with a higher risk of COVID-19 complications, such as ICU admission, assisted ventilation, and the increased markers levels of COVID-19 worse outcome [
55].
3. Summary
A broad spectrum of signs and symptoms were reported in association with COVID-19; however, only a few studies highlighted oral clinical manifestations observed in hospitalized patients. The pathogenesis remains unclear, but some hypotheses have been formulated. Xu et al. showed a higher expression of ACE2 in the oral mucosa, especially on the tongue and in the salivary glands [
11]. Thus, the oral cavity might be an anatomical site susceptible to SARS-CoV-2 infection [
94]. Consequently, the interaction between SARS-CoV-2 and ACE2 might dysregulate the oral keratinocytes’ function, leading to painful oral ulcers [
37]. This mechanism could also be the basis of early manifestations of COVID-19, such as taste alteration and xerostomia [
95]. The immune response to infection could activate Langerhans cells and lymphocytes, leading to vasculitis and thrombocytopenia, causing oral lesions related to vascular disorders (e.g., petechiae) [
19,
41,
92,
96].
It is still unclear whether oral lesions reflect a direct viral cytopathic effect or represent a consequence of stress, poor oral hygiene, systemic infections, medical treatments, or medical devices used during hospital admission [
97]. However, to the best of our knowledge, no attempt has been made to review the available literature regarding oral lesions in hospitalized COVID-19 patients. Therefore, this systematic review is the first to characterizs the patterns of oral lesions that occurred in hospitalized patients affected by COVID-19. As intraoral examination has not yet been considered in the screening of the disease, literature still lacks evidence to better understand the onset of oral manifestations. In this review, the most common oral lesions seen in patients before hospital admission are painful ulcers, cheilitis, and tongue lesions. According to several authors, these lesions are related directly to COVID-19 [
36,
37,
88,
89]. Conversely, the most common oral lesions displayed by patients during hospitalization are perioral pressure ulcers, macroglossia, blisters, and oral candidiasis. These lesions may be due to the long-lasting prone position of ICU patients [
21,
90], increased pressure of the endotracheal tubes [
59], prolonged inpatient care [
52], persistent immunological impairment [
43,
47], and medical treatments [
80].
Although the evidence derived from case series and case reports is very low, a strong recommendation for oral lesions of hospitalized patients, affected by COVID-19, can be provide. Moreover, GRADE literature describes five paradigmatic situations in which a strong recommendation can be made based on low quality evidence, such as a condition of life threatening [
99].
It could be suggest that: (1) painful oral ulcers, cheilitis, and tongue lesions are more frequent in patients before hospital admission; (2) perioral pressure ulcers, macroglossia, blisters, and oral candidiasis are more evident in patients during hospitalization; (3) lesions that appeared before hospital admission are mainly related directly to COVID-19; (4) lesions that appeared during hospitalization are mainly associated with medical devices and treatments, prone position, and immunological impairment; (5) all clinicians, during the hospital admission, should be encouraged to perform an accurate oral examination of all confirmed COVID-19 cases to recognize the disease’s possible early manifestations; (6) further studies are necessary to establish the pathological significance of oral manifestations during COVID-19.