Multisystem inflammatory syndrome in children in Child
MIS-C occurs 2-6 weeks after COVID-19 infection, and many patients were asymptomatic or only mildly symptomatic during acute infection.
The true incidence of MIS-C is unknown. A study based in New York City cited an incidence rate of 11.4 cases per 100 000 individuals under the age of 20. The median age of onset is 8 years, but cases in infants and young adults have been reported. Black children and children of Hispanic descent are disproportionally affected. Children with MIS-C are typically otherwise healthy. Obesity is the most commonly documented medical condition, seen in 30% of MIS-C cases. The fatality rate of MIS-C is reported at 1%-2%, approximately 10-fold higher than previous reports of Kawasaki disease (KD). Reports of multisystem inflammatory syndrome in adults (MIS-A) are also reported.
While the definitive etiology of this syndrome is still unknown, it is thought to be a postinfectious, dysregulated immune response to SARS-CoV-2 virus infection. SARS-CoV-2 may act as a superantigen to drive the hyperinflammatory response. Increased IFN-γ response markers suggest this cytokine may drive MIS-C-associated inflammation.
The typical presentation of MIS-C is fevers for 3-5 days, gastrointestinal symptoms (abdominal pain, vomiting, diarrhea), KD-like mucocutaneous features, and shock. Gastrointestinal symptoms are documented in 60%-90% of patients and can be so intense that they may mimic appendicitis. Other features include sore throat, myalgia, swollen hands / feet, and lymphadenopathy. Unlike acute COVID-19 infection, acute respiratory symptoms are not common in MIS-C, and only one-third of all patients have cough.
Mucocutaneous features overlap with those seen in KD and can serve as an important clue in the initial evaluation of a child with MIS-C. The most common features include a nonpurulent conjunctivitis, hyperemia and cracking of the lips, strawberry tongue, and palmoplantar erythema. MIS-C exanthems may be urticarial, morbilliform, or scarlatiniform. Potentially unique features seen in MIS-C include upper eyelid erythema that may mimic a heliotrope rash and periorbital edema. In contrast to classic KD, desquamation in the groin is uncommon or absent. The presence of mucocutaneous features is not a predictor of disease severity, and there is no specific histopathology.
A critical feature of MIS-C is the risk for cardiac dysfunction and the need for hemodynamic support. Myocardial dysfunction indicated by either echocardiography or elevated troponin or brain natriuretic peptide (BNP) is seen in over 50% of reported cases. Children who present with shock have several distinguishing features including older age, being Black, not fulfilling criteria for typical or atypical KD, neurologic symptoms, respiratory symptoms, and higher inflammatory markers (specifically ferritin, C-reactive protein [CRP], D-dimer).
MIS-C children presenting with shock have more severe disease with higher rates of intensive care unit (ICU) admission, longer length of stay, and increased mortality. This MIS-C subgroup is also more likely to suffer from neurocognitive symptoms, including headache, confusion, irritability, and lethargy. Severe neurologic symptoms include hyporeflexia, generalized weakness, meningeal signs, and encephalopathy.
Younger children are more likely to present with features seen in typical or atypical KD, and older children are more likely to present with shock and greater disease severity.
On May 14, 2020, the CDC published its case definition (see Look For).
M35.81 – Multisystem inflammatory syndrome
895448002 – Multisystem inflammatory syndrome in children