Haemophagocytic syndrome presenting as pyrexia of unknown origin.

Haemophagocytic syndrome (HPS) should be included in the differential diagnosis of pyrexia of unknown origin (PUO). The hallmark of HPS is the accumulation of activated macrophages that engulf haematopoietic cells in the reticuloendothelial system. We describe a patient with unexplained fever in which a final diagnosis of HPS was established in a bone marrow study.