COVID-19 chilblain-like lesion: immunohistochemical demonstration of SARS-CoV-2 spike protein in blood vessel endothelium and sweat gland epithelium in a polymerase chain reaction-negative patient

Engineering Materials and Devices for the Prevention, Diagnosis, and Treatment of COVID-19 and Infectious Diseases

Following the global spread of COVID-19, scientists and engineers have adapted technologies and developed new tools to aid in the fight against COVID-19. This review discusses various approaches to engineering biomaterials, devices, and therapeutics, especially at micro and nano levels, for the prevention, diagnosis, and treatment of infectious diseases, such as COVID-19, serving as a resource for scientists to identify specific tools that can be applicable for infectious-disease-related research, technology development, and treatment. From the design and production of equipment critical to first responders and patients using three-dimensional (3D) printing technology to point-of-care devices for rapid diagnosis, these technologies and tools have been essential to address current global needs for the prevention and detection of diseases. Moreover, advancements in organ-on-a-chip platforms provide a valuable platform to not only study infections and disease development in humans but also allow for the screening of more effective therapeutics. In addition, vaccines, the repurposing of approved drugs, biomaterials, drug delivery, and cell therapy are promising approaches for the prevention and treatment of infectious diseases. Following a comprehensive review of all these topics, we discuss unsolved problems and future directions.

Pemphigus Vulgaris Possibly Associated with COVID-19 Infection

Pemphigus vulgaris (PV) represents damage to epidermal keratinocytes, resulting in acantholysis due to the production of autoantibodies against desmoglein-1 and desmoglein-3. Autoimmune blistering disorders such as pemphigus vulgaris or bullous pemphigoid that develop following coronavirus disease 2019 (COVID-19) have been reported in several studies. Herein, we report a case of PV onset following COVID-19 infection in a 17-year-old female, demonstrating --the potential pathogenic capacity of SARS-CoV-2 to develop PV.

Cutaneous vasculitis: Lessons from COVID-19 and COVID-19 vaccination

Cutaneous vasculitis (CV) is an inflammatory skin-limited vascular disease affecting the dermal and/or hypodermal vessel wall. From the pathogenetic point of view, idiopathic forms are described as well as the induction from various triggers, such as drugs, infections, and vaccines. Following SARS-CoV-2 pandemic outbreak, cases of CV induced by both COVID-19 and COVID-19 vaccinations have been reported in literature. The aim of our work was to collect multiple cases available in the literature and analyze the frequency of the different forms of induced vasculitis, as well as their histological and immunopathological features. Although rare, CV induced by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and vaccines may provide interesting insights into the pathogenesis of these inflammatory processes that may in the future be useful to understand the mechanisms underlying cutaneous and systemic vasculitis.

The Impact of COVID-19 Pandemic on Dermatological Conditions: A Novel, Comprehensive Review

Background: The earliest cases of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) emerged in Wuhan, China, in December 2019. Since the declaration as a pandemic on 11 March 2020, further dermatological conditions continue to be documented. We herein present a novel literature review of dermatological manifestations associated with the Coronavirus Disease 2019 (COVID-19) pandemic. To date, this literature review is the first broad-spectrum examination that analyzes a range of dermatological manifestations related to the COVID-19 pandemic: infection, vaccinations, personal protective equipment (PPE), and psychosocial factors. Methods: A detailed literature search was conducted using key terms for cutaneous manifestations associated with the scope of this review. The search retrieved 2199 articles. Results: The COVID-19 pandemic has triggered a significant range of dermatologic sequela. Etiologies of lesions continue to be investigated. Proposed mechanisms include inflammatory response to spike protein, vitamin D deficiency, ACE2 receptor activation, androgen levels, and increased psychological stress. One prominent mechanism describes viral spike protein invasion into the dermis by binding to the angiotensin-converting enzyme 2 (ACE-2) receptors in keratinocytes, with a secondary immunological response. Conclusions: Dermatologists play an integral role in the proper diagnosis and treatment of COVID-related lesions. Early treatment regimens and timely prophylaxis have been shown to safely reduce infection-related dermatological sequelae. Additional investigations and data collection can reduce disease burden and improve overall prognosis.

Histopathological and Immunohistochemical Characterization of Skin Biopsies From 41 SARS-CoV-2 (+) Patients: Experience in a Mexican Concentration Institute: A Case Series and Literature Review

ABSTRACT

The SARS-CoV-2 pandemic brought countless clinical and pathophysiological questions. Although mucocutaneous infections are the most visible, they are among the least studied. This article provides relevant information to characterize morphologically and immunohistochemically the dermatoses from patients with COVID-19, during the first year of the pandemic. Immunohistochemistry reactions against the spike protein were performed in 48 skin biopsies, and the positive cases were classified according to their histomorphology; at the end, 41 biopsies led us to identify 12 morphological patterns that mimic other skin pathologies, among which pityriasiform patterns predominate. For the literature review, we selected cases of SARS-CoV-2 dermatoses that included complete histopathological information and that were published during the same interval of time; after careful evaluation, 205 biopsies were selected and then classified into 8 groups according to previously published proposals. Dermatoses associated with SARS-CoV-2 are as diverse in their clinical expression as in their histopathology, mimicking entities totally unrelated to COVID-19. Furthermore, some of these groups are characteristically associated with an aggressive course of the disease. Undoubtedly, it is necessary to delve into the possibility that these findings are translatable into prognostic and therapeutic factors.

Pandemic chilblains: Are they SARS-CoV-2-related or not?

The exact etiopathology of chilblains observed during the Coronavirus Disease 2019 (COVID-19) pandemic is still unclear. Initially, SARS-CoV-2 appeared as the obvious causing agent, but two years of various investigations have failed to convincingly support its direct implication. Most affected individuals have no detectable virus, no anti-SARS-CoV-2 antibodies and no symptoms of COVID-19. Analyses of skin biopsies similarly failed to unambiguously demonstrate presence of the virus or its genome. In a recent hypothesis, SARS-CoV-2 would cause the lesions before being promptly eliminated by unusually strong type I interferon responses. With others, we feel that environmental factors have not been sufficiently considered, in particular cold exposure related to unprecedented containment measures. The cause of pandemic chilblains remains a stimulating puzzle which warrants further investigation.

Oral Manifestations of Coronavirus Disease 2019 (COVID-19): A Comprehensive Clinicopathologic and Immunohistochemical Study

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) presents rapid transmission and significant mortality worldwide. It is responsible for coronavirus disease 2019 (COVID-19). The disease presents diverse clinical symptoms, including fever, cough, dyspnea, and pneumonia. However, other manifestations associated with COVID-19 need to be clarified, leading specialists to an early diagnosis and better prognosis. We describe the spectrum of clinicopathologic COVID-19-related oral lesions that can be the first and/or the unique manifestation of the disease. Fourteen patients with a mean age of 58 years (range: 23 to 88 y) with oral lesions were included. All patients were confirmed to be infected with SARS-CoV-2 by reverse transcription polymerase chain reaction testing. Patients demonstrated mild symptoms, including dysgeusia, anosmia, fever, and headache. The lesions were recognized and classified into 2 groups: (1) lesions caused by ischemia and/or hemorrhage and (2) lesions secondary to inflammatory events associated with viral load. The palate was most affected (n=8), followed by the tongue (n=4), and both the lip and palate (n=2). Histologic analysis demonstrated thrombosis of small arteries and capillaries, associated with areas of hemorrhage and chronic inflammatory infiltrate. Immunohistochemistry showed positive staining for spike protein (SARS-CoV and SARS-CoV-2) and angiotensin-converting enzyme 2 in the surface epithelium, salivary glands, inflammatory cells, and endothelial cells. Although the incidence of oral lesions among patients infected with SARS-CoV-2 appears to be uncommon, these findings suggest that the oral mucosa can also be a target organ for SARS-CoV-2.

Extensive cutaneous leukocytoclastic vasculitis after Sinopharm vaccine: case report and review of the literature

Cutaneous leukocytoclastic vasculitis (LCV) has been reported as a rare form of cutaneous reaction to different SARS-Cov-2 vaccines. Herein, we present the first case of cutaneous LCV following BBIBP-CorV (Sinopharm) vaccine, that occurred in a female patient with no prior comorbidities. A literature review about similar cases following different COVID-19 vaccines is discussed. This article is protected by copyright. All rights reserved.

Rare and common manifestations of COVID-19 in children

Introduction

It has been almost 2 years since the first reports on cutaneous manifestations of COVID-19. Those reported in children are different and include macular, papular, lichenoid, vesicular, urticarial, and vascular morphologies, among others. The prognosis of isolated cutaneous involvement in COVID-19 in children is usually self-limiting but the extreme variety of clinical presentations complicates the clinical approach.

Methods

Numerous reviews have been systematically drafted and edited giving the clinicians a future direction for skin presentations during pandemics.

Results and Discussion

Hereby we report the rare and common manifestations of COVID-19 in children and question the recurrence phenomena and age-related distribution of the eruptions.

A Standardization Protocol for the In Situ Detection of SARS-CoV2 RNA and Proteins

This manuscript details a stringent protocol for the in situ detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) RNA and 4 different viral proteins: envelope, spike, membrane, and nucleocapsid. Key aspects of the protocol are: (1) analysis of adjacent (serial) sections for viral RNA and at least 2 viral proteins; (2) cytologic alterations in the cells scored as virus positive based on an hematoxylin and eosin stain; (3) in situ demonstration of a host response in the cells scored as virus positive; (4) co-labeling experiments that show that the viral RNA and/or proteins co-localize with each other and the angiotensin converting enzyme 2 (ACE2) receptor; and (5) lack of signal in equivalent tissues obtained before the pandemic. Optimization conditions for the four viral proteins as well as the ACE2 receptor were each antigen retrieval in an EDTA solution which facilitates co-expression analyses. It is recommended not to use either electron microscopy or qRTPCR as methods to corroborate in situ SARS-CoV2 detection. This stringent protocol, that relies on sequentially labeled serial sections and can be completed in one working day, demonstrated the following: (1) infectious SARS-CoV2 is abundant in the lung in fatal coronavirus disease-2019 and is seen primarily in macrophages and endothelial cells; (2) circulating viral capsid proteins (spike, envelope, membrane without RNA) are evident in multiple organs including the skin and brain where it is endocytosed by ACE2+ cells and induce an endothelialitis; (3) both the infectious virus and circulating spike protein induce complement activation and cytologic changes in the viral positive cells.

SARS-CoV-2 might transmit through the skin while the skin barrier function could be the mediator

During the coronavirus disease 2019 (COVID-19) pandemic, it were reported that COVID-19 patients could have cutaneous symptoms, and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was observed on the skin of COVID-19 patients, which indicated that the skin is one target of SARS-CoV-2. Meanwhile, reports about SARS-CoV-2 transmission through food cold-chain overpacks emerged. With the fact that SARS-CoV-2 could survive on the skin for more than 9 h, the skin could be implicated in SARS CoV-2 transmission. Angiotensin-converting enzyme 2 (ACE2), a critical membrane protein for SARS-CoV-2 that enters a host cell, was recognized to be associated with the risk of SARS-CoV-2 infection. Therefore, tissues that express ACE2 might have the potential to be infected by and transmit SARS-CoV-2. The skin is one such tissue that expresses ACE2. However, unlike the lung that expresses ACE2 on the upper-most epithelial layer, the skin is composed of different layers of cells that function as a barrier, and cells under the top epidermal layer express ACE2. Since the skin barrier is the first line of protection, the typical position of ACE2-expressing cells in the skin implies that the skin barrier function could be the mediator of SARS-CoV-2. In our study, we found that ACE2 could be expressed in the skin, and its expression level is increased in psoriasis, an inflammatory disease of the skin with barrier dysfunction. Additionally, by applying the SARS-CoV-2 pseudovirus on mouse models with or without deteriorated skin barrier, we found that the SARS-CoV-2 pseudovirus could infect the skin and lungs of mouse models, and when the skin barrier was impaired, more SARS-CoV-2-infected cells could be found. Thus, we hypothesized that a deteriorated condition of the skin barrier might increase the risk of SARS-CoV-2 infection through the skin.

Clinicopathologic features among different viral epidemic outbreaks involving the skin

The current coronavirus disease 2019 pandemic has exceeded any epidemiologic prevision, but increasing information suggests some analogies with the major viral outbreaks in the last century, and a general warning has been issued on the possibility that coinfections can make the differential diagnosis and treatment difficult, especially in tropical countries. Some reports have noted that the presence of high dengue antibodies can give a false-negative result when testing for severe acute respiratory syndrome coronavirus 2. Mucocutaneous manifestations are very frequent, with an apparent overlap among different pathogens. However, strong clinicopathologic correlation might provide some clues to address differentials. Waiting for laboratory and instrumental results, the timing and distribution of skin lesions is often pathognomonic. Histopathologic findings characterize certain reaction patterns and provide insights on pathogenetic mechanisms. Unfortunately, skin assessment, especially invasive examinations such as biopsy, takes a back seat in severely ill patients. A literature retrieval was performed to collect information from other epidemics to counteract what has become the most frightening disease of our time.

RNAscope in situ hybridization and RT-PCR for detection of SARS-CoV-2 in chilblain-like lesions: A clinical, laboratory and histopathological study

BACKGROUND

Since the beginning of the coronavirus disease 2019 (COVID-19) pandemic, an increasing number of chilblain-like lesions (ChLL) have been increasingly reported worldwide. To date, the causal link between ChLL and SARS-CoV-2 infection has not been unequivocally established.

METHODS

In this case series, we present demographic, clinical, laboratory, and histopathological information regarding 27 young patients with a clinical diagnosis of ChLL who referred to the Dermatology Unit of Papa Giovanni XXIII Hospital, Bergamo, Italy, from 1 April 2020 to 1 June 2020.

RESULTS

The mean age was 14.2 years, and 21 patients (78%) experienced mild systemic symptoms a median of 28 days before the onset of cutaneous lesions. ChLL mostly involved the feet (20 patients - 74%). Among acral lesions, we identified three different clinical patterns: (i) chilblains in 20 patients (74%); (ii) fixed erythematous macules in 4 children (15%); (iii) erythrocyanosis in 3 female patients (11%). Blood examinations and viral serologies, including parvovirus B19, cytomegalovirus (CMV), Epstein-Barr virus (EBV), and coxsackievirus were normal in all. Three patients (11%) underwent nasopharyngeal swab for RT-PCR for SARS-CoV-2 showing only 1 positive. Histopathological examinations of 7 skin biopsies confirmed the clinical diagnosis of chilblains; vessel thrombi were observed only in 1 case. Our findings failed to demonstrate the direct presence of SARS-CoV-2 RNA in skin biopsies, both with real-time polymerase chain reaction (RT-PCR) and RNAscope in situ hybridization (ISH).

LIMITATIONS

Limited number of cases, unavailability of laboratory confirmation of COVID-19 in all patients, potential methodological weakness, and latency of skin biopsies in comparison to cutaneous lesions onset.

CONCLUSIONS

These observations may support the hypothesis of an inflammatory pathogenesis rather than the presence of peripheral viral particles. Although, we could not exclude an early phase of viral endothelial damage followed by an IFN-I or complement-mediated inflammatory phase. Further observations on a large number of patients are needed to confirm this hypothesis.

Recent Advancements on COVID-19: A Comprehensive Review

Over the last few decades, there have been several global outbreaks of severe respiratory infections. The causes of these outbreaks were coronaviruses that had infected birds, mammals and humans. The outbreaks predominantly caused respiratory tract and gastrointestinal tract symptoms and other mild to very severe clinical signs. The current coronavirus disease-2019 (COVID-19) outbreak, caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a rapidly spreading illness affecting millions of people worldwide. Among the countries most affected by the disease are the United States of America (USA), India, Brazil, and Russia, with France recording the highest infection, morbidity, and mortality rates. Since early January 2021, thousands of articles have been published on COVID-19. Most of these articles were consistent with the reports on the mode of transmission, spread, duration, and severity of the sickness. Thus, this review comprehensively discusses the most critical aspects of COVID-19, including etiology, epidemiology, pathogenesis, clinical signs, transmission, pathological changes, diagnosis, treatment, prevention and control, and vaccination.

Cutaneous Leukocytoclastic Vasculitis Induction Following ChAdOx1 nCoV-19 Vaccine

The coronavirus disease 2019 (COVID-19) pandemic is an unprecedented event, and in order to control its spread and minimize its damages, all efforts are immediately mobilized. Mass vaccination is considered a promising solution to combat this universal issue. However, given the urgent need for vaccine production, some of the side effects may not have been presented during trials and will only appear during the mass vaccination. Limited vasculitis cases have been reported so far following vaccination against COVID-19. We present a case of cutaneous leukocytoclastic vasculitis (LCV) induced following the first dose of the ChAdOx1 nCoV-19 vaccine in an otherwise healthy individual.

From Your Nose to Your Toes: A Review of Severe Acute Respiratory Syndrome Coronavirus 2 Pandemic‒Associated Pernio

Despite thousands of reported patients with pandemic-associated pernio, low rates of seroconversion and PCR positivity have defied causative linkage to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Pernio in uninfected children is associated with monogenic disorders of excessive IFN-1 immunity, whereas severe COVID-19 pneumonia can result from insufficient IFN-1. Moreover, SARS-CoV-2 spike protein and robust IFN-1 response are seen in the skin of patients with pandemic-associated pernio, suggesting an excessive innate immune skin response to SARS-CoV-2. Understanding the pathophysiology of this phenomenon may elucidate the host mechanisms that drive a resilient immune response to SARS-CoV-2 and could produce relevant therapeutic targets.

Endothelial contribution to COVID-19: an update on mechanisms and therapeutic implications

The global propagation of SARS-CoV-2 leads to an unprecedented public health emergency. Despite that the lungs are the primary organ targeted by COVID-19, systemic endothelial inflammation and dysfunction is observed particularly in patients with severe COVID-19, manifested by elevated endothelial injury markers, endotheliitis, and coagulopathy. Here, we review the clinical characteristics of COVID-19 associated endothelial dysfunction; and the likely pathological mechanisms underlying the disease including direct cell entry or indirect immune overreactions after SARS-CoV-2 infection. In addition, we discuss potential biomarkers that might indicate the disease severity, particularly related to the abnormal development of thrombosis that is a fatal vascular complication of severe COVID-19. Furthermore, we summarize clinical trials targeting the direct and indirect pathological pathways after SARS-CoV-2 infection to prevent or inhibit the virus induced endothelial disorders.

Skin manifestations associated with COVID-19

This article will address the main aspects of skin manifestations associated with COVID-19, based on a review of the literature published to date. Since the beginning of the pandemic, more than 1,500 articles have been published on the subject. Regarding the pathophysiology, it is believed that the same mechanisms responsible for the disease in the main target organs also act in the skin, although they are not yet fully elucidated. The actual frequency of dermatological manifestations remains uncertain – it can range from 0.2% to 45%, being close to 6% in systematic reviews. Pioneering studies of large case series conducted in European countries and the USA provide the first information on the main skin manifestations associated with COVID-19 and propose classifications regarding their clinical presentation, pathophysiology, as well as their frequencies. Although there is yet no consensus, maculopapular eruptions are considered the most frequent presentations, followed by erythema pernio-like (EPL) lesions. Manifestations such as urticaria, vesicular conditions and livedo/purpura/necrosis are rare. The time of onset, severity, need for specific treatment and prognosis vary according to the clinical presentation pattern. The increasing histopathological description of skin conditions can contribute to the diagnosis, as well as to the understanding of the pathophysiology. Also, in the dermatological field, the relationship between COVID-19 and androgens has been increasingly studied. Despite all the generated knowledge, the actual biological meaning of skin manifestations remains uncertain. Therefore, the exclusion of the main differential diagnoses is essential for the correlation between skin manifestation and COVID-19.

Clinical Patterns and Morphology of COVID-19 Dermatology

Coronavirus disease 2019 (COVID-19), an emergent disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has rapidly spread throughout the globe since its discovery in December 2019. Although first appreciated to cause pneumonia, numerous organ systems are now known to be involved. The objective of this article is to review the broad spectrum of cutaneous manifestations reported in association with SARS-CoV-2 infection. The most commonly reported cutaneous manifestations associated with COVID-19 infection include pernio (chilblain)-like acral lesions, morbilliform (exanthematous) rash, urticaria, vesicular (varicella-like) eruptions, and vaso-occlusive lesions (livedo racemosa, retiform purpura). It is important to consider SARS-CoV-2 infection in the differential diagnosis of a patient presenting with these lesions in the appropriate clinical context, as cutaneous manifestations may be present in otherwise asymptomatic individuals, or present before developing other symptoms of infection. With increased access to diagnostic testing, we are beginning to understand the utility and limitations of currently available assays.

Cutaneous manifestations in children with SARS-CoV-2 infection and/or COVID-19: what do we know after 10 months under this pandemic?

BACKGROUND

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a global crisis. However, cutaneous manifestations in children with SARS-CoV-2 infection have received little attention.

OBJECTIVE

Our study was aimed to present clinical and cutaneous manifestations of children with SARS-CoV-2 and to provide the basis for early diagnosis.

METHODS

We analyzed the clinical data of COVID-19 infected (CI) children worldwide from December 2019 to October 6, 2020, by using search terms "COVID-19," "SARS-CoV-2," "Coronavirus" in combination with "cutaneous," "lesion," "rash," "skin," "dermatology," "epidermis," "dermis," "multisystem inflammatory syndrome." We collected and analyzed the general information, clinical symptoms, cutaneous manifestations, laboratory examination results, history of close contact with CI patients or suspected CI patients, and outcome in CI children.

RESULTS

Among 90 CI children, there were 46 boys (59%) and 32 girls (41%). Erythema was the most frequent lesion, followed by conjunctivitis, and edematous lesions. Face was the most commonly affected location including lips, conjunctivae, tongue, eyes, and eyelids. Sixty-three (73.3%) patients had multisystem inflammatory syndrome (MIS-C). As for clinical symptoms, 70 (81.4%) CI children suffered fever, and 34 (39.5%) patients had lung involvement. Meanwhile, 65.1% of patients had cardiac involvement, 4.7% of patients were asymptomatic, and 71.6% of patients received intravenous immunoglobulin, as well as 31.1% of CI children received systemic corticosteroids. Three children were dead. The most frequent route of infection was familial clustering. As silent virus carriers of CI children, it is important to find out the clinical and cutaneous manifestations in CI children to prevent and control COVID-19 transmission.

Clinicopathologic features between different viral epidemic outbreaks involving the skin

The current coronavirus disease 2019 pandemic has exceeded any epidemiologic prevision, but increasing information suggests some analogies with the major viral outbreaks of the last century. A general warning has been issued on the possibility that coinfections can make differential diagnosis and treatment difficult, especially in tropical countries. Some reports have pointed out that the presence of high Dengue antibodies can give a false-negative result for severe acute respiratory syndrome coronavirus 2. Mucocutaneous manifestations are very frequent, with an apparent overlap among different pathogens. A strong clinicopathologic correlation, however, may provide some clues to address the differential. Waiting for laboratory and instrumental results, the timing and distribution of skin lesions is often pathognomonic. Histopathologic findings characterize certain reaction patterns and provide insights on pathogenetic mechanisms. Unfortunately, skin assessments, especially invasive exams such as biopsy, are less important in severely ill patients. A literature review was performed to collect information from other epidemics to counteract what has become the most frightening disease of our time.

Papulo-purpuric dermatitis of childhood: a distinct PLEVA-like eruption associated to SARS-CoV-2 infection. Clinical, histopathological and immunohistochemical study of 10 cases

We observed ten children with a papular eruption with purpuric features during the SARS-CoV-2 pandemic in Northern Italy (May-December 2020). Histological examination showed signs of SARS-CoV-2-related dermatosis. Evidence of nucleocapsid viral proteins using SARS-CoV-2 (2019-nCoV) nucleocapsid antibody revealed cuticular staining of the deep portion of the eccrine glands in all cases.

A clinicopathological description of COVID-19-induced chilblains (COVID-toes) correlated with a published literature review

Background

The abundance of publications of COVID‐19‐induced chilblains has resulted in a confusing situation.

Methods

This is a prospective single‐institution study from 15 March to 13 May 2020. Thirty‐two patients received PCR nasopharyngeal swabs. Of these, 28 patients had a thoracic CT‐scan, 31 patients had blood and urine examinations, 24 patients had skin biopsies including immunohistochemical and direct immunofluorescence studies, and four patients had electron microscopy.

Results

COVID‐19‐induced chilblains are clinically and histopathologically identical to chilblains from other causes. Although intravascular thrombi are sometimes observed, no patient had a systemic coagulopathy or severe clinical course. The exhaustive clinical, radiological, and laboratory work‐up in this study ruled‐out other primary and secondary causes. Electron microscopy revealed rare, probable viral particles whose core and spikes measured from 120 to 133 nm within endothelium and eccrine glands in two cases.

Conclusion

This study provides further clinicopathologic evidence of COVID‐19‐related chilblains. Negative PCR and antibody tests do not rule‐out infection. Chilblains represent a good prognosis, occurring later in the disease course. No systemic coagulopathy was identified in any patient. Patients presenting with acral lesions should be isolated, and chilblains should be distinguished from thrombotic lesions (livedo racemosa, retiform purpura, or ischemic acral necrosis).

A Review of COVID-19 Chilblains-like Lesions and Their Differential Diagnoses

GENERAL PURPOSE

To familiarize wound care practitioners with the differential diagnoses of chilblains-like lesions that could be associated with the complications of COVID-19.

TARGET AUDIENCE

This continuing education activity is intended for physicians, physician assistants, nurse practitioners, and nurses with an interest in skin and wound care.

LEARNING OBJECTIVES/OUTCOMES

After participating in this educational activity, the participant will:1. Identify the population most often affected by COVID toes.2. Select the assessments that help differentiate the various conditions that cause chilblains-like lesions.3. Choose appropriate treatment options for the various conditions that cause chilblains-like lesions.

Dermatological Manifestations Associated with COVID-19 Infection

The severe acute respiratory syndrome corona virus 2 (SARS-CoV-2) causing the 2019 coronavirus disease (COVID-19) has infected millions in recent years and is a major public health concern. Various cutaneous manifestations of the COVID-19 disease have been identified. Skin is a mirror to internal disease and can be the presenting sign of COVID-19 disease. Several cutaneous manifestations can indicate severe COVID-19 disease. In the present scenario, physicians should know the various cutaneous manifestations of COVID-19 disease for early diagnosis and proper management of the disease.

Pernio (Chilblains), SARS-CoV-2, and COVID Toes Unified Through Cutaneous and Systemic Mechanisms

Pernio or chilblains is characterized by erythema and swelling at acral sites (eg, toes and fingers), typically triggered by cold exposure. Clinical and histopathologic features of pernio are well described, but the pathogenesis is not entirely understood; vasospasm and a type I interferon (IFN-I) immune response are likely involved. During the coronavirus disease 2019 (COVID-19) pandemic, dermatologists have observed an increase in pernio-like acral eruptions. Direct causality of pernio due to COVID-19 has not been established in many cases because of inconsistent testing methods (often negative results) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, a form of COVID-19‒associated pernio (also called COVID toes) is probable because of increased occurrence, frequently in young patients with no cold exposure or a history of pernio, and reports of skin biopsies with positive SARS-CoV-2 immunohistochemistry. PubMed was searched between January 1, 2020, and December 31, 2020 for publications using the following keywords: pernio, chilblain, and acral COVID-19. On the basis of our review of the published literature, we speculate that several unifying cutaneous and systemic mechanisms may explain COVID-19‒associated pernio: (1) SARS-CoV-2 cell infection occurs through the cellular receptor angiotensin-converting enzyme 2 mediated by transmembrane protease serine 2, subsequently affecting the renin-angiotensin-aldosterone system with an increase in the vasoconstricting, pro-inflammatory, and prothrombotic angiotensin II pathway. (2) Severe acute respiratory syndrome coronavirus 2 cell infection triggers an immune response with robust IFN-I release in patients predisposed to COVID-19‒associated pernio. (3) Age and sex discrepancies correlated with COVID-19 severity and manifestations, including pernio as a sign of mild disease, are likely explained by age-related immune and vascular differences influenced by sex hormones and genetics, which affect susceptibility to viral cellular infection, the renin-angiotensin-aldosterone system balance, and the IFN-I response.

Idiopathic perniosis presenting as acral purpuric lesions: Clustering of cases before COVID-19 pandemic and their comparison with chilblain like lesions reported in the literature

Perniosis/chilblains are the acral inflammatory skin lesions developing in susceptible individuals as an abnormal reaction to cold. In the absence of a discernible cause, it is labeled as idiopathic perniosis (IP). With the ongoing COVID-19 pandemic, there was an upsurge of reports of chilblain like lesions (CLL) especially in young patients possibly implicated to the SARS-CoV-2 virus. Twelve clinically suspected and histopathologically confirmed cases of IP seen from November 2019 through February 2020 were retrospectively recruited. Clinical, dermoscopic, and histopathological characteristics of these were reviewed and compared with CLL reported in the literature. Mean age of patients was 26.58 ± 15.18 years with an equal male to female ratio. Characteristic histopathology findings were spongiosis (100%), dermal edema (100%), perivascular lymphocytic infiltrate (100%) with peri-eccrine accentuation (66.7%), keratinocyte necrosis (50%), focal basal vacuolar damage (58.3%), and lymphocytic vasculitis (58.3%). Significant dermoscopy findings were variable background color ranging from dull red and violaceous to copper red and brown orange, coiled vessels (44.4%) and orange-red structureless areas (63.9%). Lesions over palms and soles preferentially had white dots/clods and lines (38.9%). There appears no exclusive histopathological as well as dermoscopy features of CLL and IP, yet certain clues can be appreciated. Keratinocyte necrosis and severe dermal edema favors IP, whereas fibrin thrombi with involvement of both superficial and deep dermal vessels favor CLL. Dermoscopically presence of irregular, linear or branching vessels, red/purple dots and clods and gray brown reticule supports CLL while white dots/clods and lines supports IP.

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2): a Systemic Infection

To date, seven identified coronaviruses (CoVs) have been found to infect humans; of these, three highly pathogenic variants have emerged in the 21st century. The newest member of this group, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was first detected at the end of 2019 in Hubei province, China. Since then, this novel coronavirus has spread worldwide, causing a pandemic; the respiratory disease caused by the virus is called coronavirus disease 2019 (COVID-19). The clinical presentation ranges from asymptomatic to mild respiratory tract infections and influenza-like illness to severe disease with accompanying lung injury, multiorgan failure, and death. Although the lungs are believed to be the site at which SARS-CoV-2 replicates, infected patients often report other symptoms, suggesting the involvement of the gastrointestinal tract, heart, cardiovascular system, kidneys, and other organs; therefore, the following question arises: is COVID-19 a respiratory or systemic disease? This review aims to summarize existing data on the replication of SARS-CoV-2 in different tissues in both patients and ex vivo models.

Associations between COVID-19 and skin conditions identified through epidemiology and genomic studies

BACKGROUND

Coronavirus disease 2019 (COVID-19) is commonly associated with skin manifestations, and may also exacerbate existing skin diseases, yet the relationship between COVID-19 and skin diseases remains unclear.

OBJECTIVE

By investigating this relationship through a multiomics approach, we sought to ascertain whether patients with skin conditions are more susceptible to COVID-19.

METHODS

We conducted an epidemiological study and then compared gene expression across 9 different inflammatory skin conditions and severe acute respiratory syndrome coronavirus 2-infected bronchial epithelial cell lines, and then performed a genome-wide association study transdisease meta-analysis between COVID-19 susceptibility and 2 skin diseases (psoriasis and atopic dermatitis).

RESULTS

Skin conditions, including psoriasis and atopic dermatitis, increase the risk of COVID-19 (odds ratio, 1.55; P = 1.4 × 10-9) but decrease the risk of mechanical ventilation (odds ratio, 0.22; P = 8.5 × 10-5). We observed significant overlap in gene expression between the infected normal bronchial epithelial cells and inflammatory skin diseases, such as psoriasis and atopic dermatitis. For genes that are commonly induced in both the severe acute respiratory syndrome coronavirus 2 infection and skin diseases, there are 4 S100 family members located in the epidermal differentiation complex, and we also identified the "IL-17 signaling pathway" (P = 4.9 × 10-77) as one of the most significantly enriched pathways. Furthermore, a shared genome-wide significant locus in the epidermal differentiation complex was identified between psoriasis and severe acute respiratory syndrome coronavirus 2 infection, with the lead marker being a significant expression quantitative trait locus for S100A12 (P = 3.3 × 10-7).

CONCLUSIONS

Together our findings suggest association between inflammatory skin conditions and higher risk of COVID-19, but with less severe course, and highlight shared components involved in anti-COVID-19 immune response.

SARS-CoV-2, COVID-19, skin and immunology - What do we know so far?

The pandemic condition coronavirus disease (COVID-19), caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), can take asymptomatic, mild, moderate, and severe courses. COVID-19 affects primarily the respiratory airways leading to dry cough, fever, myalgia, headache, fatigue, and diarrhea and can end up in interstitial pneumonia and severe respiratory failure. Reports about the manifestation of various skin lesions and lesions of the vascular system in some subgroups of SARS-CoV-2-positive patients as such features outside the respiratory sphere, are rapidly emerging. Vesicular, urticarial, and maculopapular eruptions and livedo, necrosis, and other vasculitis forms have been reported most frequently in association with SARS-CoV-2 infection. In order to update information gained, we provide a systematic overview of the skin lesions described in COVID-19 patients, discuss potential causative factors, and describe differential diagnostic evaluations. Moreover, we summarize current knowledge about immunologic, clinical, and histologic features of virus- and drug-induced lesions of the skin and changes to the vascular system in order to transfer this knowledge to potential mechanisms induced by SARS-CoV-2.

Molecular Insights into the Thrombotic and Microvascular Injury in Placental Endothelium of Women with Mild or Severe COVID-19

Clinical manifestations of coronavirus disease 2019 (COVID-19) in pregnant women are diverse, and little is known of the impact of the disease on placental physiology. Severe acute respiratory syndrome coronavirus (SARS-CoV-2) has been detected in the human placenta, and its binding receptor ACE2 is present in a variety of placental cells, including endothelium. Here, we analyze the impact of COVID-19 in placental endothelium, studying by immunofluorescence the expression of von Willebrand factor (vWf), claudin-5, and vascular endothelial (VE) cadherin in the decidua and chorionic villi of placentas from women with mild and severe COVID-19 in comparison to healthy controls. Our results indicate that: (1) vWf expression increases in the endothelium of decidua and chorionic villi of placentas derived from women with COVID-19, being higher in severe cases; (2) Claudin-5 and VE-cadherin expression decrease in the decidua and chorionic villus of placentas from women with severe COVID-19 but not in those with mild disease. Placental histological analysis reveals thrombosis, infarcts, and vascular wall remodeling, confirming the deleterious effect of COVID-19 on placental vessels. Together, these results suggest that placentas from women with COVID-19 have a condition of leaky endothelium and thrombosis, which is sensitive to disease severity.

The JANUS of chronic inflammatory and autoimmune diseases onset during COVID-19 - A systematic review of the literature

The diverse clinical manifestations of COVID-19 is emerging as a hallmark of the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) infection. While the initial target of SARS-CoV-2 is the respiratory tract, it is becoming increasingly clear that there is a complex interaction between the virus and the immune system ranging from mild to controlling responses to exuberant and dysfunctional multi-tissue directed autoimmune responses. The immune system plays a dual role in COVID-19, being implicated in both the anti-viral response and in the acute progression of the disease, with a dysregulated response represented by the marked cytokine release syndrome, macrophage activation, and systemic hyperinflammation. It has been speculated that these immunological changes may induce the loss of tolerance and/or trigger chronic inflammation. In particular, molecular mimicry, bystander activation and epitope spreading are well-established proposed mechanisms to explain this correlation with the likely contribution of HLA alleles. We performed a systematic literature review to evaluate the COVID-19-related autoimmune/rheumatic disorders reported between January and September 2020. In particular, we investigated the cases of incident hematological autoimmune manifestations, connective tissue diseases, antiphospholipid syndrome/antibodies, vasculitis, Kawasaki-like syndromes, acute arthritis, autoimmune-like skin lesions, and neurologic autoimmune conditions such as Guillain-Barré syndrome. We screened 6263 articles and report herein the findings of 382 select reports which allow us to conclude that there are 2 faces of the immune response against SARS-CoV-2, that include a benign virus controlling immune response and a many faceted range of dysregulated multi-tissue and organ directed autoimmune responses that provides a major challenge in the management of this viral disease. The number of cases for each disease varied significantly while there were no reported cases of adult onset Still disease, systemic sclerosis, or inflammatory myositis.

SARS-CoV-2 and endothelial cell interaction in COVID-19: molecular perspectives

SARS-CoV-2 is the agent responsible for the coronavirus disease (COVID-19), which has been declared a pandemic by the World Health Organization. The clinical evolution of COVID-19 ranges from asymptomatic infection to death. Older people and patients with underlying medical conditions, particularly diabetes, cardiovascular and chronic respiratory diseases are more susceptible to develop severe forms of COVID-19. Significant endothelial damage has been reported in COVID-19 and growing evidence supports the key pathophysiological role of this alteration in the onset and the progression of the disease. In particular, the impaired vascular homeostasis secondary to the structural and functional damage of the endothelium and its main component, the endothelial cells, contributes to the systemic proinflammatory state and the multiorgan involvement observed in COVID-19 patients. This review summarizes the current evidence supporting the proposition that the endothelium is a key target of SARS-CoV-2, with a focus on the molecular mechanisms involved in the interaction between SARS-CoV-2 and endothelial cells.

Acute acral eruptions in children during the COVID-19 pandemic: Characteristics of 103 children and their family clusters

Background

A marked increase in frequency of acute acral eruptions (AAE) was observed in children during the COVID-19 pandemic in the spring period.

Objectives

In this observational multicenter study, based on children with AAE, we aimed to assess the proportion of household members possibly infected by SARS-CoV-2.

Methods

We collected data from all children observed with AAE, prospectively from April 7, 2020 to June 22, 2020, and retrospectively since February 28, 2020. The primary outcome was the household infection rate, defined as the proportion of family clusters having at least one member with COVID-19 infection other than the child with AAE (“index child”). The definition of a case was based on characteristic clinical signs and a positive PCR or serology.

Results

The study included 103 children in 10 French departments and in Quebec. The median age was 13 years and the interquartile range [8–15], with a female-to-male ratio of 1/1.15. In children with AAE, all PCR tests were negative (n = 18), and serology was positive in 2/14 (14.3%) cases. We found no significant anomalies in the lab results. A total of 66 of the 103 families (64.1%) of included children had at least one other infected member apart from the index child. The total number of household members was 292, of whom 119 (40.8%) were considered possibly infected by SARS-CoV-2. No index children or households exhibited severe COVID-19.

Discussion

Among the 103 households included, 64.1% had at least one infected member. Neither children with AAE nor their households showed severe COVID-19.

Chilblain-Like Lesions during COVID-19 Pandemic: The State of the Art

SARS-CoV-2 infection has spread all over the world in the last year, causing millions of COVID-19 cases among humans with a large variability of symptoms and signs, including those on the skin. Among these, a contemporary cluster of chilblain-like lesions with no certain relationship with the infection has been reported. The aim of this paper is to delineate a profile of chilblain-like lesions and to establish the state-of-the-art knowledge about this new phenomenon.

COVID toes: where do we stand with the current evidence?

BACKGROUND

Numerous of cases of chilblains have been observed, mainly in young subjects with no or mild symptoms compatible with COVID-19. The pathophysiology of these lesions is still widely debated and an association with SARS-CoV-2 infection remains unconfirmed.

OBJECTIVES

This paper focus on the unresolved issues about these COVID toes and in particular whether or not they are associated with COVID-19.

ARGUMENTS

The temporal link between the outbreak of chilblains and the COVID-19 pandemic is a first suggests a link between the two events. Positive anti-SARS-CoV/SARS-CoV-2 immunostaining on skin biopsy of chilblains seem to confirm the presence of the virus in the lesions, but lack specificity and must be interpreted with caution. Conversely, RT-PCR and anti-SARS-CoV-2 serology were negative in the majority of patients with chilblains. Therefore, SARS-CoV-2 infection can be excluded, with relative certainty, even after accounting for possible lower immunization in mild/asymptomatic patients and for some differences in sensitivity/specificity between the tests used. Some authors hypothesize that chilblains could be the cutaneous expression of a strong type I interferon (IFN-I) response. High production of IFN-I is suggested to be associated with early viral control and may suppress antibody response. However, the absence of other cutaneous or extracutaneous symptoms as observed in other interferonopathies raises unanswered questions. To date, a direct link between chilblains and COVID-19 still seems impossible to confirm. A more indirect association due to lifestyle changes induced by lockdown is a possible explanation. Improvement of chilblains when protective measures were adopted and after lifting of lockdown, support this hypothesis.

CONCLUSION

Conflicting current evidence highlights the need for systematic and repeated testing of larger numbers of patients and the need for valid follow-up data that take into consideration epidemic curves and evolution of lockdown measures.

Clinicopathologic correlations of COVID-19-related cutaneous manifestations with special emphasis on histopathologic patterns

Skin is one of target organs affected by the novel coronavirus SARS-CoV-2, and in response to the current COVID-19 pandemic, a fast body of literature has emerged on related cutaneous manifestations. Current perspective is that the skin is not only a bystander of the general cytokines storm with thrombophilic multiorgan injury, but it is directly affected by the epithelial tropism of the virus, as confirmed by the detection of SARS-CoV-2 in endothelial cells and epithelial cells of epidermis and eccrine glands. In contrast with the abundance of epidemiologic and clinical reports, histopathologic characterization of skin manifestations is limited. Without an adequate clinicopathologic correlation, nosology of clinically similar conditions is confusing, and effective association with COVID-19 remains presumptive. Several patients with different types of skin lesions, including the most specific acral chilblains-like lesions, showed negative results at SARS-CoV-2 nasopharyngeal and serologic sampling. The aim of this review is to provide an overview of what has currently been reported worldwide, with a particular emphasis on microscopic patterns of the skin manifestations in patients exposed to or affected by COVID-19. Substantial breakthroughs may occur in the near future from more skin biopsies, improvement of immunohistochemistry studies, RNA detection of SARS-CoV-2 strain by real-time polymerase chain reaction-based assay, and electron microscopic studies.

SARS-CoV-2 spike protein is present in both endothelial and eccrine cells of a chilblain-like skin lesion

Data on SARS‐CoV‐2 detection in lesional skin is controversial.^1‐8 We report a PCR‐proven COVID‐19 patient with a chilblain‐like SARS‐CoV‐2 positive skin lesion. An 80‐year‐old woman presented to the emergency department at the End of March 2020. She reported an onset of fever (38.4 C°) several days before admission, along with cough and shortness of breath. RT‐PCR from a nasopharyngeal swab was positive for SARS‐CoV‐2. An X‐ray showed evidence for right‐sided pneumonic infiltrates.

Type I Interferon Signature in Chilblain-Like Lesions Associated with the COVID-19 Pandemic

Contemporarily to the new SARS-CoV-2 mediated COVID-19 pandemic, a rise in patients with acral chilblain lesions has been described. They manifest late after mild disease or asymptomatic exposure to SARS-CoV-2. Their pathogenic evolution is currently unknown. In biopsies from three patients with acral partially ulcerating chilblain lesions that occurred associated to the COVID-19 pandemic, we analysed the expression of type I interferon induced proteins and signal transduction kinases. Histology demonstrated perivascular and periadnexal lymphohistiocytic infiltrates and endothelial dominated MxA-staining, as well as pJAK1 activation. Our findings demonstrate induction of the type I IFN pathway in lesional sections of COVID-19-associated chilblain-like lesions. This may indicate a local antiviral immune activation status associated with preceding exposure to SARS-CoV-2.

Study presence of COVID-19 (SARS-CoV-2) in the sweat of patients infected with Covid-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) disease, which started in Wuhan, Chin, has now become a public health challenge in most countries around the world. Proper preventive measures are necessary to prevent the spread of the virus to help control the pandemic. Because, SARS-CoV-2 is new, its transmission route has not been fully understood. In this study, we aimed to investigate the presence of SARS-CoV-2 in the sweat secretion of COVID-19 patients. Sweat specimens of 25 COVID- 19 patients were collected and tested for SARS-CoV-2 RNA by Real-time Polymerase Chain Reaction (RT-PCR) method. After RNA extraction and cDNA amplification, all samples were examined for the presence of ORF-1ab and N genes related to COVID-19. Results annotated by Realtime PCR machines software based on Dynamic algorithm. The results of this study showed the absence of SARS-CoV-2 in the sweat samples taken from the foreheads of infected people. Therefore, it can be concluded that the sweat of patients with COVID- 19 cannot transmit SARS-CoV-2. However they can be easily contaminated with other body liquids.

Discordant anti-SARS-CoV-2 spike protein and RNA staining in cutaneous perniotic lesions suggests endothelial deposition of cleaved spike protein

BACKGROUND

Prior studies have shown the presence of immunohistochemical staining for the SARS-CoV-2 spike protein (SP) in endothelial cells and eccrine epithelium of acral perniosis classified as "COVID toes." Yet, other studies have been unable to detect SARS-CoV-2 RNA in skin biopsies of "COVID toes" by reverse-transcriptase polymerase chain reaction testing.

OBJECTIVE

In order to address these apparently conflicting findings, we compared detection of SARS-CoV-2 SP, through RNA in situ hybridization (ISH) vs immunohistochemistry (IHC), in skin biopsies of acral perniotic lesions presenting during the COVID-19 pandemic.

RESULTS

Three of six cases showed positive immunohistochemical labeling of endothelial cells, with one of three cases with sufficient depth also having labeling of eccrine glands, using an anti-SP SARS-CoV-2 antibody. These three cases positive with IHC were negative for SP by RNA ISH.

CONCLUSION

While the gold standard for detection of SARS-CoV-2 in tissue sections has yet to be determined, the detection of SARS-CoV-2 SP alone without spike RNA suggests that cleaved SP may be present in cutaneous endothelial cells and eccrine epithelium, providing a potential pathogenetic mechanism of COVID-19 endotheliitis.

Familial clustering of COVID-19 skin manifestations

The medical community in the past months has seen a flourishing of information related to the SARS‐CoV‐2 virus responsible for the COVID‐19 pandemic. From the early days of the pandemic, the SARS‐CoV‐2 virus has been linked to multiple different types of skin involvement. To the best of our knowledge, we are the first to report on a case of familial clustering of a maculopapular COVID‐19 rash. Eight persons presented COVID‐19 symptoms, six were confirmed via SAR‐CoV‐2 chemoluminescent immunoassays, and the four related by blood presented skin manifestations. Although, it has not been fully established if the SARS‐CoV‐2 can in fact cause viral exanthems, our observations regarding the familial clustering and the temporal evolution seen in this family seem to present strong evidence of a viral exanthema related to SARS‐CoV‐2 infection.

Clinical and Histopathological Features and Potential Pathological Mechanisms of Skin Lesions in COVID-19: Review of the Literature

In recent weeks, several reports have emerged of skin lesions with different clinical presentations in COVID-19 cases. All dermatologists should be aware of these cutaneous lesions, which may be early clinical symptoms of infection. We reviewed the literature on cutaneous manifestations in the PubMed database from December 2019 and June 2020. From the cases described as case reports or series in 57 recent articles, it appears that skin lesions (i) are highly varied, (ii) may not be related to the severity of the condition and (iii) resolve spontaneously in a few days. The frequency of these lesions in COVID-19 patients varies between 1.8% and 20.4%. The major clinical forms described were maculopapular eruptions, acral areas of erythema with vesicles or pustules (pseudochilblain), urticarial lesions, other vesicular eruptions and livedo or necrosis. The lesions were mainly localized in the trunk and extremities. The majority of patients were male, aged between 4.5 and 89 years. A minority of the patients were children presenting with acral, chilblain-like lesions, papulo-vesicular eruptions or Kawasaki disease-like pediatric inflammatory multisystem syndrome. The mean duration of the lesions was a few days, but some lasting as little as 20 min and others as long as four weeks have been reported. The mean latency time in the majority of cases was between 1 and 14 days; however, in some patients, lesions appeared 2 to 5 days before the onset of COVID-19 symptoms. The histopathological features of these lesions also vary, corresponding to the diversity of clinical manifestations. These features underline the nature of epidermal and dermal vascular lesions-and in severe cases, microvascular injury and thrombosis-associated with COVID-19, and provide important clues to their pathological mechanisms.