hematology and oncology
Hemophagocytic Lymphohistiocytosis (HLH)
Introduction
Hemophagocytic lymphohistiocytosis (HLH) is an uncommon disorder causing immune dysfunction in infants and young children. Many patients have an underlying immune disorder, although in some patients the underlying disorder is not known. Manifestations may include lymphadenopathy, hepatosplenomegaly, fever, and neurologic abnormalities. Diagnosis is by specific clinical and testing (genetic) criteria. Treatment is usually with chemotherapy and, in refractory cases or in cases with a genetic cause, hematopoietic stem cell transplantation. (See also Overview of Histiocytic Disorders .) Hemophagocytic lymphohistiocytosis (HLH) is uncommon. It affects mostly infants<18 months but can occur at any age. It involves a defect in targeted killing and the inhibitory controls of natural killer and cytotoxic T cells, resulting in excessive cytokine production and accumulation of activated T cells and macrophages in various organs. Cells in the bone marrow and/or spleen may attack red blood cells, white blood cells, and/or platelets. HLH can be Familial (primary) Acquired (secondary) HLH is diagnosed when patients fulfill at least 5 of the criteria described below or have a mutation in a known HLH-associated gene. Acquired HLH can be associated with infections (eg, Infectious Mononucleosis , In both familial and acquired forms, clinical manifestations are similar. 