Influenza B Virus Triggering Macrophage Activation Syndrome in an Infant.

Macrophage activation syndrome (MAS) is a potentially fatal complication caused by excessive activation and expansion of macrophages and T lymphocytes. It can be triggered by various infections and is characterized by the development of cytopenias, hyperferritinemia, liver dysfunction, and coagulopathy. We report a 10-month-old female infant with fever, convulsions, and hepatosplenomegaly. Laboratory data of bicytopenia, low erythrocyte sedimentation rate, and elevated liver enzymes suggested MAS. This was supported by the presence of hyperferritinemia with hypertriglyceridemia. MAS was triggered by influenza B virus. She responded to treatment with immunoglobulin and steroid.