Hemophagoctic lymphohistiocytosis--recent concept.

Hemophagocytic lymphohistiocytosis is a rare condition characterized by highly stimulated but inactive immune response. The disease may be inherited or acquired due to infections, collagen vascular diseases and malignancies. The pathological hallmark of the syndrome is aggressive proliferation of macrophages and histiocytes. Decreased NK cell activity results in increased T cell activation resulting production of large quantities of interferon gamma (IFN gamma), tumor necrosis factor alpha (TNF alpha) and granulocyte macrophage colony stimulating factor (GM-CSF). This causes sustained macrophage activation and tissue infiltration as well as production of interleukin 1 (IL1) and interleukin 6 (IL6).The resulting inflammatory reaction causes extensive damage and associated symptoms. Patients with HLH commonly present with high fever, anemia and splenomegaly. Minimal diagnostic parameters are a complete hemogram, liver function test, serum triglycerides and ferritin, coagulation profile including fibrinogen and bone marrow aspiration. Two highly sensitive diagnostic marker are an increased plasma concentration of the alpha chain of soluble IL2 receptor (CD25) and impaired NK cell activity. Hyperinflammation can be treated with steroid, Cyclosporine prevents T lymphocytes and immunoglobulin infusion helps to control the infection. Etoposide may be life saving specially in case of HLH with Ebstein Barr Viruses infection. The Histiocyte Society in 1994 developed a common treatment protocol (HLH-94). In January 2004 a revised HLH treatment protocol was opened entitled HLH-2004, which is based on HLH-94 with minor modifications. There is a high remission rate on the HLH-94 and HLH-2004 treatment protocols.