349: Secondary Hemophagocytic Lymphohistiocytosis in an Older Adult With Persistent Fever: A Case Report

Introduction: Hemophagocytic lymphohistiocytosis (HLH) is a rare and life‐threatening cytokine-storm-type disorder characterized by the excessive activity of the immune and inflammatory systems. HLH can be primary (genetic, childhood onset) or secondary (acquired from infection, malignancies, or autoimmune diseases, adult onset). We report a case of an older adult male with persistent fever who was found to have elevated CD25 and diagnosed with HLH. Description: An 82-year-old man with known history of chronic lymphocytic leukemia (CLL), COPD, HTN, insulin dependent DM, paroxysmal atrial fibrillation, and hypothyroidism was admitted to intensive care unit with acute hypoxemic respiratory failure secondary to community acquired pneumonia (CAP), sepsis, and septic shock requiring intubation and mechanical ventilation. He improved with broad-spectrum IV antibiotics and weaned off vasopressors but remained ventilator-dependent. A few days later, he clinically deteriorated with high-grade fever (up to 41°C), anemia, thrombocytopenia, altered mental status and new requirements for vasoactive agents. Despite empiric antibiotics (for possible health care associated pneumonia), antifungals (for suspected disseminated candidiasis), and extensive infectious workup (all non-diagnostic), symptoms persisted. Hematology was consulted and raised suspicion for HLH. Work up confirmed HLH (meeting >5 criteria: fever, splenomegaly, bicytopenia, hypofibrinogenemia 1650 ng/mL (ref: 24-340 ng/mL), and elevated soluble IL-2 receptor 42450 pg/ml (ref: 532-1891 pg/ml). Patient was started on IV dexamethasone 20 mg/day, with rapid clinical improvement: defervescense, mental status improvement, vasopressor wean, and successful extubation. Patient was prescribed steroid taper and eventually discharged home. The likely trigger for his HLH was underlying CLL versus recent CAP. Discussion: Diagnosis of HLH is based on meeting at least 5 out of 8 HLH-2004 criteria, often supported by elevated soluble IL-2 receptor (sCD25) and, in familial cases, genetic mutations (e.g., PRF1, UNC13D). Due to its nonspecific presentation and rarity, HLH is often difficult to diagnose. Persistent fever may be the earliest or only sign. Given the high mortality, early recognition and prompt treatment are critical.