Hemophagocytic lymphohistiocytosis

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Hemophagocytic lymphohistiocytosis (HLH) is an unusual syndrome characterized by fever, splenomegaly, jaundice, and the pathologic finding of hemophagocytosis. This is phagocytosis by macrophages of erythrocytes, leukocytes, platelets, and their precursors in bone marrow and other tissues.

HLH may be associated with malignant, genetic, or autoimmune diseases. It is also prominently linked with Epstein-Barr virus (EBV) infection, however it can also be associated with other viruses as well as fungal infections.

Hyperproduction of cytokines, including interferon-g and tumor necrosis factor-a, by EBV-infected T lymphocytes may play a role in the pathogenesis of HLH. EBV-associated HLH may mimic T-cell lymphoma and is treated with cytotoxic chemotherapy. In contrast, hemophagocytic syndromes associated with nonviral pathogens often respond to treatment of the underlying infection.

HLH comprises familial (primary) hemophagocytic lymphohistiocytosis (FHL) and secondary HLH (SHLH), both clinically characterized by the features described above, in particular fever, hepatosplenomegaly, and cytopenia.

Familial forms

FHL, an autosomal recessive disease, is invariably fatal when untreated. It is associated with defective triggering of apoptosis and reduced cytotoxic activity, resulting in a widespread accumulation of T lymphocytes and activated macrophages.

There are four types, and each is associated with a specific gene:

• FHL1 - HPLH1
• FHL2 - PRF1
• FHL3 - UNC13D
• FHL4 - STX11

References

• Fisman DN (2000). "Hemophagocytic syndromes and infection". Emerging Infect. Dis. 6 (6): 601–8. PMID 11076718.

• Henter JI, Samuelsson-Horne A, Aricò M, et al (2002). "Treatment of hemophagocytic lymphohistiocytosis with HLH-94 immunochemotherapy and bone marrow transplantation". Blood 100 (7): 2367–73. doi:10.1182/blood-2002-01-0172. PMID 12239144.