COVID-19 and multisystem inflammatory syndrome in children: SAQ

This school-age child has the signature presentation of multisystem inflammatory syndrome in children: persistent fever with multiorgan involvement (gastrointestinal symptoms, mucocutaneous features, shock), markedly raised inflammatory markers, an elevated troponin, and a SARS-CoV-2 exposure three weeks earlier. His delayed capillary refill, tachycardia, and hypotension indicate early shock, and the elevated troponic signalling cardiac involvement makes the echocardiogram the pivotal next investigation. ^[1]

Question 1 (10 marks)

Outline your diagnostic approach including the key investigations and their interpretation in this child. ^[1]

The diagnosis of multisystem inflammatory syndrome in children rests on persistent fever, laboratory evidence of inflammation, multiorgan involvement, and current or recent SARS-CoV-2 infection or exposure with no alternative diagnosis. This child meets the clinical criteria on persistent fever, gastrointestinal and mucocutaneous involvement, and shock, with a temporally related SARS-CoV-2 exposure three weeks earlier. ^[1]

Send the full inflammatory and cardiac panel: a full blood count, which typically shows neutrophilia, lymphopaenia, and thrombocytopaenia; C-reactive protein, ferritin, fibrinogen, lactate dehydrogenase, and triglycerides, all markedly raised; coagulation studies including a markedly raised D-dimer; albumin, which is typically low; and electrolytes, with hyponatraemia common. The cardiac biomarkers are pivotal: troponin and B-type natriuretic peptide or its N-terminal propeptide define cardiac involvement and guide the intensity of monitoring and the escalation of immunomodulation. ^[1]

The SARS-CoV-2 testing requires care because the infection was weeks earlier. A negative nasopharyngeal polymerase chain reaction is expected and does not exclude the diagnosis; immunoglobulin G serology should be sent and is positive in most children, supporting the post-infectious mechanism. Blood culture and targeted microbiology exclude sepsis and its mimics. An electrocardiogram screens for arrhythmia and conduction abnormality. ^[1]

The echocardiogram is mandatory and is the test that most directly changes management: it assesses left and right ventricular function, valve regurgitation, pericardial effusion, and the coronary arteries, with coronary dimensions reported as Z-scores so that aneurysms are detected against age-appropriate norms. In this child the elevated troponic signals myocardial involvement, so the echocardiogram is urgent. ^[1]