An unusual cause of fever.

A 5-month old infant presented with a short history of fever of unknown origin. He initially appeared well although there was a resting tachycardia during periods of normal temperature, and pancytopenia. He remained febrile in spite of antibiotic therapy and by 48 h he had developed marked hepatosplenomegaly and coagulopathy. At 72 h a bone marrow aspirate and trephine biopsy showed haemophagocytosis. By this time the infant was encephalopathic and haemodynamically unstable with multi-organ dysfunction. Treatment with high-dose methylprednisolone and cyclosporin was commenced with an initial good response. Unfortunately the patient ultimately died of infective complications of treatment and reactivation of the underlying disease process. Haemophagocytic lymphohistiocytosis (HLH) is a rare disorder of the mononuclear phagocyte system characterised by proliferation of morphologically benign histiocytes resulting in hypercytokinaemia and uncontrolled activation of immune cells. The diagnosis of familial HLH should be considered in any infant with fever, splenomegaly and cytopenia of at least two cell lines. HLH may be cured by immunosuppressive therapy and eventual stem cell transplantation but rapid disease progression to multi-organ failure results in a high mortality.