Secondary Hemophagocytic Lymphohistiocytosis in a Patient With Crohn's Disease Receiving Infliximab: A Diagnostic Challenge.

Hemophagocytic lymphohistiocytosis (HLH) is a rare, life-threatening hyperinflammatory syndrome caused by uncontrolled immune activation. While pediatric HLH is well-recognized, adult cases often mimic sepsis or autoimmune flares, delaying diagnosis. Inflammatory bowel disease (IBD) and its immunosuppressive treatments, including infliximab, have been increasingly linked to HLH. We report a 65-year-old man with Crohn's disease on infliximab who presented with persistent fever, chills, night sweats, headaches, and bradycardia. Laboratory testing revealed pancytopenia, hyperferritinemia (32,531 ng/mL), hypertriglyceridemia (11.5 mmol/L), hypofibrinogenemia (0.3 g/L), and elevated inflammatory markers. Infectious and autoimmune workups were negative, while CT imaging showed right upper lobe ground-glass opacities. Bone marrow biopsy demonstrated histiocytic hyperplasia with hemophagocytosis. The patient fulfilled HLH-2004 diagnostic criteria and had a high H-score. Infliximab was discontinued, and high-dose corticosteroids were initiated, resulting in marked clinical improvement without the need for etoposide. This case highlights infliximab-associated HLH in an IBD patient and emphasizes the importance of early diagnosis using established criteria. Clinicians should consider HLH in immunosuppressed patients presenting with unexplained systemic inflammation and cytopenias, as timely recognition and tailored therapy can significantly improve survival.