Fever of Unknown Cause: A Case of Macrophage Activation Syndrome

Fever of unknown origin (FUO) in children is a challenging diagnostic problem, as it can be caused by a wide range of infectious, inflammatory, malignant, or genetic disorders. We present the case of a 12-year-old girl with persistent fever, arthralgia, and elevated inflammatory markers. Despite extensive infectious, oncological, and rheumatologic investigations, no underlying cause was identified. Laboratory findings revealed markedly increased C-reactive protein, ferritin, and D-dimer levels, and mild hepatomegaly. Macrophage activation syndrome (MAS) was suspected due to persistent fever and hyperferritinemia, and confirmed by bone marrow aspiration. The patient responded rapidly to intravenous immunoglobulin and high-dose corticosteroids. This case emphasizes the importance of considering MAS in pediatric FUO and highlights the need for early recognition and treatment.