[Multisystem inflammatory syndrome in a young infant with lymphocytosis and reactive thrombocytosis post COVID-19:...

Multisystem inflammatory syndrome in children (MIS-C) is a rare, but serious complication associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, characterized by persistent fever, systemic inflammation, and multiorgan involvement. It predominantly affects school-aged children and adolescents. Reports in infants under 1 year are limited, and atypical presentations pose diagnostic challenges.

8-month-old male infant who presented with 10 days of persistent fever, diarrhea, and irritability. Initial laboratory findings revealed leukocytosis, marked thrombocytosis, persistent lymphocytosis, and significantly elevated liver enzymes. No mucocutaneous findings or cardiac involvement were noted. The diagnosis of MIS-C was established based on Centers for Disease Control and Prevention (CDC) criteria and confirmed by positive IgG serology for SARS-CoV-2. Treatment with intravenous immunoglobulin (IVIg), aspirin, and corticosteroids achieved a favorable clinical and biochemical evolution.

This case highlights an atypical presentation of MIS-C in a young infant, with hematological findings that differ from classic patterns. Early recognition and standard immunomodulatory therapy led to a successful outcome. Documenting such variants is essential to expand our understanding of MIS-C in underrepresented age groups.