Massive idiopathic pericardial effusion in a pediatric patient responsive to interleukin-1 receptor antagonist: Unveiling an undercover hyperinflammation?

We report a child with massive, chronic idiopathic pericardial effusion (PE), initially detected incidentally and asymptomatically. Despite multiple treatment attempts, including Nonsteroidal anti-inflammatory drugs, corticosteroids, colchicine, and repeated pericardiocentesis, the effusion persisted and recurred. Advanced imaging revealed a stable but severe PE over the years, with no hemodynamic compromise. Cytokine analysis of the pericardial fluid showed markedly elevated interleukin (IL)-6 levels, suggesting an underlying inflammatory process despite the absence of classic clinical signs. Based on this finding, the patient was successfully treated with anakinra, an IL-1 receptor antagonist, resulting in sustained remission for 24 months. This case highlights the potential role of biologic therapy in selected pediatric patients with chronic idiopathic PE, even when traditional markers of inflammation are absent. Cytokine profiling may help identify candidates for anti-IL-1 treatment, providing a valuable therapeutic option where standard approaches fail.