Abstract
Multisystem inflammatory syndrome in children (MIS-C) is a rare, delayed hyperinflammatory response, which occurs 2-6 weeks after SARS-CoV-2 infection. Main symptoms include fever, involvement of at least two organ systems, elevated inflammatory markers and evidence of infection with or exposure to SARS-CoV-2. While the prognosis is generally favorable, complications-such as myocardial dysfunction, coronary aneurysms, and coagulation disorders-can lead to severe outcomes, including death. Immunomodulatory and antithrombotic therapies are key components of treatment. We report a clinical case of a 3-year-old boy who developed MIS-C, initially presenting with fever, multiorgan involvement, and confirmed SARS-CoV-2 infection, along with a coinfection caused by group A β-hemolytic Streptococcus (GAS) isolated from throat culture. On the ninth day of illness, thrombosis of the right subclavian vein was detected. Subsequent genetic testing for thrombophilia revealed that the patient was a heterozygous carrier of Factor V Leiden, Factor V HR2, and PAI-1 4G/5G polymorphisms. Thromboembolic events (TEs) are serious and potentially life-threatening complications of MIS-C. This case highlights the occurrence of TE in a 3-year-old boy, an age group younger than typically observed, emphasizing the need for heightened awareness, early detection, and prompt intervention. Additionally, it underscores the importance of careful monitoring of thrombotic risks in MIS-C patients, particularly those with underlying prothrombotic conditions, to prevent severe outcomes.