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Multisystem inflammatory syndrome associated with the SARS-CoV-2 pandemic has recently been described in children (MIS-C), partially overlapping with Kawasaki disease (KD). We hypothesized that (a) MIS-C and prepandemic KD cytokine profiles may be unique and justify the clinical differences observed, and (b) SARS-CoV-2-specific immune complexes (ICs) may explain the immunopathology of MIS-C. Seventy-four children were included: 14 with MIS-C, 9 patients positive for SARS-CoV-2 by PCR without MIS-C (COVID), 14 with prepandemic KD, and 37 healthy controls (HCs). Thirty-four circulating cytokines were quantified in pretreatment serum or plasma samples and the presence of circulating SARS-CoV-2 ICs was evaluated in MIS-C patients. Compared with HCs, the MIS-C and KD groups showed most cytokines to be significantly elevated, with IFN-γ-induced response markers (including IFN-γ, IL-18, and IP-10) and inflammatory monocyte activation markers (including MCP-1, IL-1α, and IL-1RA) being the main triggers of inflammation. In linear discriminant analysis, MIS-C and KD profiles overlapped; however, a subgroup of MIS-C patients (MIS-Cplus) differentiated from the remaining MIS-C patients in IFN-γ, IL-18, GM-CSF, RANTES, IP-10, IL-1α, and SDF-1 and incipient signs of macrophage activation syndrome. Circulating SARS-CoV-2 ICs were not detected in MIS-C patients. Our findings suggest a major role for IFN-γ in the pathogenesis of MIS-C, which may be relevant for therapeutic management.

Kawasaki disease (KD) is a pediatric vasculitis with coronary artery aneurysms (CAA) as its main complication. The diagnosis is based on the presence of persistent fever and clinical features including exanthema, lymphadenopathy, conjunctival injection, and changes to the mucosae and extremities. Although the etiology remains unknown, the current consensus is that it is likely caused by an (infectious) trigger initiating an abnormal immune response in genetically predisposed children. Treatment consists of high dose intravenous immunoglobulin (IVIG) and is directed at preventing the development of CAA. Unfortunately, 10–20% of all patients fail to respond to IVIG and these children need additional anti-inflammatory treatment. Coronary artery lesions are diagnosed by echocardiography in the acute and subacute phases. Both absolute arterial diameters and z -scores, adjusted for height and weight, are used as criteria for CAA. Close monitoring of CAA is important as ischemic symptoms or myocardial infarction due to thrombosis or stenosis can occur. These complications are most likely to arise in the largest, so-called giant CAA. Apart from the presence of CAA, it is unclear whether KD causes an increased cardiovascular risk due to the vasculitis itself. Conclusion : Many aspects of KD remain unknown, although there is growing knowledge on the etiology, treatment, and development and classification of CAA. Since children with previous KD are entering adulthood, long-term follow-up is increasingly important. What is known: • Kawasaki disease (KD) is a pediatric vasculitis with coronary artery damage as its main complication . • Although KD approaches its 50th birthday since its first description, many aspects of the disease remain poorly understood . What is new: • In recent years, multiple genetic candidate pathways involved in KD have been identified, with recently promising information about the ITPKC pathway . • As increasing numbers of KD patients are reaching adulthood, increasing information is available about the long-term consequences of coronary artery damage and broader cardiovascular risk .

Key Points Epidemiologic data strongly suggest an infectious aetiology for Kawasaki disease, which is the leading cause of acquired heart disease among children in developed countries Necrotizing arteritis, subacute chronic vasculitis, and luminal myofibroblastic proliferation are three linked processes underlying the arteriopathy associated with Kawasaki disease Genetic susceptibility is indicated by the strikingly high rate of Kawasaki disease in children of Asian ethnicity and by its increased incidence in first-degree relatives of affected patients Timely diagnosis and treatment of Kawasaki disease with intravenous immunoglobulin (IVIg) and aspirin substantially decreases the risk of developing coronary artery abnormalities Adjunctive therapy with corticosteroids is of value in Japanese patients at particularly high risk of coronary complications, but identification of such high-risk patients is difficult in ethnically diverse populations Management of patients who do not respond to standard therapy is challenging; options include pulsed steroids, additional IVIg, and infliximab or other immunomodulatory agents Considerable progress has been made in understanding the pathologic processes and pathophysiology of Kawasaki disease. This article also discusses genetic susceptibility to Kawasaki disease and describes current approaches to treatment of the acute stage of the disease. This Review summarizes recent advances in understanding of the pathologic processes and pathophysiologic mechanisms leading to coronary arteritis in Kawasaki disease, and describes current approaches to its treatment. Kawasaki disease is the most common cause of acquired heart disease among children in developed countries, in whom the resulting coronary artery abnormalities can cause myocardial ischaemia, infarction and even death. Epidemiologic data strongly suggest an infectious aetiology, although the causative agent has yet to be identified. Genetic factors also increase susceptibility to Kawasaki disease, as indicated by its strikingly high incidence rate in children of Asian ethnicity and by an increased incidence in first-degree family members. The treatment of Kawasaki disease is based on timely administration of intravenous immunoglobulin and aspirin. However, the management of patients who do not respond to this standard therapy remains challenging; although several options are available, comparative data on which to base treatment decisions are scarce. The added value of adjunctive therapy with corticosteroids in patients at particularly high risk of coronary complications has been demonstrated in Japanese populations, but identification of high-risk patients has proven to be difficult in ethnically diverse populations.

Kawasaki disease is recognized as the most common cause of acquired heart disease in children in the developed world. Clinical, epidemiologic, and pathologic evidence supports an infectious agent, likely entering through the lung. Pathologic studies proposing an acute coronary arteritis followed by healing fail to account for the complex vasculopathy and clinical course. Specimens from 32 autopsies, 8 cardiac transplants, and an excised coronary aneurysm were studied by light (n=41) and transmission electron microscopy (n=7). Three characteristic vasculopathic processes were identified in coronary (CA) and non-coronary arteries: acute self-limited necrotizing arteritis (NA), subacute/chronic (SA/C) vasculitis, and luminal myofibroblastic proliferation (LMP). NA is a synchronous neutrophilic process of the endothelium, beginning and ending within the first two weeks of fever onset, and progressively destroying the wall into the adventitia causing saccular aneurysms, which can thrombose or rupture. SA/C vasculitis is an asynchronous process that can commence within the first two weeks onward, starting in the adventitia/perivascular tissue and variably inflaming/damaging the wall during progression to the lumen. Besides fusiform and saccular aneurysms that can thrombose, SA/C vasculitis likely causes the transition of medial and adventitial smooth muscle cells (SMC) into classic myofibroblasts, which combined with their matrix products and inflammation create progressive stenosing luminal lesions (SA/C-LMP). Remote LMP apparently results from circulating factors. Veins, pulmonary arteries, and aorta can develop subclinical SA/C vasculitis and SA/C-LMP, but not NA. The earliest death (day 10) had both CA SA/C vasculitis and SA/C-LMP, and an \"eosinophilic-type\" myocarditis. NA is the only self-limiting process of the three, is responsible for the earliest morbidity/mortality, and is consistent with acute viral infection. SA/C vasculitis can begin as early as NA, but can occur/persist for months to years; LMP causes progressive arterial stenosis and thrombosis and is composed of unique SMC-derived pathologic myofibroblasts.

The coronavirus disease-2019 (COVID-19) pandemic is likely to pose new challenges to the rheumatology community in the near and distant future. Some of the challenges, like the severity of COVID-19 among patients on immunosuppressive agents, are predictable and are being evaluated with great care and effort across the globe. A few others, such as atypical manifestations of COVID-19 mimicking rheumatic musculoskeletal diseases (RMDs) are being reported. Like in many other viral infections, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection can potentially lead to an array of rheumatological and autoimmune manifestations by molecular mimicry (cross-reacting epitope between the virus and the host), bystander killing (virus-specific CD8 + T cells migrating to the target tissues and exerting cytotoxicity), epitope spreading, viral persistence (polyclonal activation due to the constant presence of viral antigens driving immune-mediated injury) and formation of neutrophil extracellular traps. In addition, the myriad of antiviral drugs presently being tried in the treatment of COVID-19 can result in several rheumatic musculoskeletal adverse effects. In this review, we have addressed the possible spectrum and mechanisms of various autoimmune and rheumatic musculoskeletal manifestations that can be precipitated by COVID-19 infection, its therapy, and the preventive strategies to contain the infection.

Kawasaki disease (KD) is a relatively common autoimmune disease of childhood, characterized by systemic vasculitis and involvement of the cardiovascular system, particularly the coronary artery. Progressive inflammatory cascades and vascular injury are regarded as two major processes underlying KD. Although it is regarded as a self-limiting disease, some children exhibit resistance to intravenous immunoglobulin (IVIG) treatment, which can lead to the development of life-threatening coronary artery aneurysms that persist into adulthood. Pyroptosis, a special inflammatory cell death pattern, results in the intense release of inflammatory mediators and injuries of tissues such as endothelial cell damage. Evidence from in vitro studies and animal models suggests that pyroptosis and associated inflammatory cascades may play a significant role in KD. Here, we highlight the latest insights into pyroptosis in KD and explore the potential therapeutic interventions that target pyroptosis.

ObjectiveKawasaki disease (KD) is an increasingly common vasculitis with risk of coronary artery aneurysms (CAAs). The last UK survey was in 1990, whereas current epidemiology, treatment patterns and complication rates are unknown. The aim of this study was to address this knowledge gap.MethodsA British Paediatric Surveillance Unit survey in the UK and Ireland from 1 January 2013 to 28 February 2015 ascertained demographics, ethnicity, seasonal incidence, treatment and complication rates.Results553 cases were notified: 389 had complete KD, 46 had atypical KD and 116 had incomplete KD; 2 were diagnosed at postmortem with an incidence of 4.55/100 000 children under 5 years, with a male to female ratio of 1.5:1 and a median age of 2.7 years (2.5 months–15 years). Presentation was highest in January and in rural areas. Most were white (64%), and Chinese and Japanese Asians were over-represented as were black African or African mixed-race children. 94% received intravenous immunoglobulin (IVIG). The overall CAA rate was 19%, and all-cardiac complications affected 28%. Those with CAA received IVIG later than in those without (median 10 days vs 7 days). Those under 1 year had fewer symptoms, but the highest CAA rate (39%). Overall 8 of 512 cases (1.6%) had giant CAA, and 4 of 86 cases (5%) under 1 year of age developed giant CAA. Mortality from KD was 0.36%.ConclusionsThe UK and Ireland incidence of KD has increased and is more frequently seen in winter and rural areas. Delayed IVIG treatment is associated with CAA, suggesting earlier and adjunctive primary treatment might reduce complications to prevent CAA, particularly in the very young.

Although data on the incidence and severity of new coronavirus disease 2019 (COVID-19) due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection showed more significant disease among adults and the elderly, a clinical manifestation characterized by a multisystem inflammatory syndrome was described in children (MIS-C). It was initially thought to be specific to children, but recent reports have shown that it can also occur in adults. MIS-C is characterized by a number of multisystemic manifestations resembling other known previously described illnesses, mainly Kawasaki disease, especially in cases with shock, toxic shock syndrome, and macrophage activation syndrome. Available literature shows that our knowledge of MIS-C is largely incomplete. Its development in strict relation with SARS-CoV-2 infection seems documented and, in most cases, can be considered a post-infectious manifestation secondary to an abnormal immune response for some aspects, similar to that seen in adults several days after SARS-CoV-2 infection. However, in a minority of cases, a clinical picture with symptoms fulfilling criteria for MIS-C diagnosis develops during the acute phase of SARS-CoV-2 infection. It is highly likely that the criteria currently used to diagnose MIS-C are too broad, meaning that children with different diseases are included. As clarity on the pathogenesis of MIS-C is lacking, different therapeutic approaches have been used, but no specific therapy is currently available. Further studies are urgently needed to improve our definition of MIS-C, to define the real impact on child health, and to elucidate the best clinical and therapeutic approach and true prognosis.

A recent surge in this disease has prompted health advisories by the US Centers for Disease Control and Prevention (CDC),1 the Royal College of Paediatrics and Child Health,2 and WHO.3 As SARS-CoV-2 spreads and awareness of MIS-C grows, the number of reported cases continues to increase. Complete blood counts showed leukocytosis (11 600–16 500 white blood cells per μL), with lymphopenia (0–700 lymphocytes per μL), neutrophilia (10 100–15 000 neutrophils per μL), atypical lymphocytosis (2% atypical lymphocytes), and increased band neutrophils (2–16% band cells), whereas comprehensive metabolic panels showed hyponatraemia (serum sodium 124–135 mmol/L) and elevated hepatic enzymes (aspartate aminotransferase [AST] 96–198 U/L; alanine aminotransferase 78–133 U/L). Emerging reports have revealed a pattern of clinical differences distinguishing MIS-C from classic Kawasaki disease.5–9 Notably, although our patient's presentation met AHA criteria for Kawasaki disease, he also exhibited many MIS-C-related features such as a predominance of gastrointestinal symptoms, generalised extremity pain, and prominent cardiac dysfunction, and his cardiac findings (elevated cardiac enzymes and left ventricular hypokinesis with a reduction in ejection fraction) resemble findings of myocarditis recently described in MIS-C.10 Furthermore, our patient's palmar lesions are distinct from the acral erythema and swelling with subsequent desquamation typically seen in Kawasaki disease, and his diffuse conjunctivitis was not limbic-sparing.

Children with Coronavirus disease 2019 (COVID-19) are being reported to have manifestations of hyperinflammatory states and/or Kawasaki-like disease. In this study, we investigated children with typical and atypical Kawasaki disease (KD) likely to be associated with COVID-19. We have reported four children with Kawasaki-like disease probably associated with COVID-19. The clinical features were consistent with incomplete KD in three patients. SARS-CoV-2 RT-PCR was positive in one and the serology was positive in one patient with negative RT-PCR. Corticosteroids, anakinra, intravenous immunoglobulin (IVIG), and acetylsalicylic acid were used in the treatment. Three patients recovered after the treatment while one patient died. The literature review revealed 36 articles describing 320 children with Kawasaki-like disease associated with COVID-19. SARS-CoV-2 RT-PCR was negative in 120 (65.5%) of 183 patients while the serology was positive in 130 (83.8%) of 155 patients. The therapeutic options have included IVIG, acetylsalicylic acid, tocilizumab, anakinra, enoxaparin, and methylprednisolone. Pediatric COVID-19 cases may present with atypical/incomplete Kawasaki-like disease. Thus, pediatricians need to be aware of such atypical presentations resembling KD for early diagnosis of COVID-19.