Prolonged fever of unknown origin and hemophagocytosis evolving into acute lymphoblastic leukemia

Hemophagocytic syndrome (HPS) is an unusual acute syndrome presenting with fever, hepatosplenomegaly, and cytopenias. The hallmark of HPS is the accumulation of activated macrophages that engulf hematopoietic cells in the reticuloendothelial system. Most cases of HPS in adults are secondary to infection or malignancy, and thus investigation of the underlying disease is necessary. We describe a patient with prolonged fever, HPS, and chromosomal abnormalities in the bone marrow who underwent thorough evaluation for the cause of his symptoms. A final diagnosis of acute lymphoblastic leukemia (ALL) was established in a fourth, repeated bone marrow biopsy performed more than 2 months after the first presenting symptom appeared. This unusual case demonstrates the importance of cytogenetic abnormalities found in cases of HPS and the importance of repeated testing when an underlying disease is suspected.