Systemic JIA is characterised not only by arthritis, but also by systemic features such as intermittent fever, lymphadenopathy, hepato-splenomegaly, exanthema and serositis. The disease occurs predominantly in childhood. It often begins at a young age and usually has a serious outcome, although new therapeutic regimes like high dose methotrexate, cyclosporine-A and TNF-α blockade have improved the prognosis.
A serious complication of systemic JIA is the Macrophage Activation Syndrome (MAS), which is often triggered by infections and medicines like gold and sulfasalazine. MAS is characterised by persistent high fever, mild to serious derangements of liver cell functions, purpura, encephalopathy and disseminated intravascular coagulation. Laboratory investigations often show a leucocytopenia, thrombocytopenia and anaemia in combination with elevated levels of bilirubin and hepatic enzymes. In the bone marrow and other organs like the lymphglands, liver and brain, haemophagocytizing histiocytes are demonstrable. Although they are not specific for MAS, the presence of haemophagocytizing histiocytes together with the other specific clinical symptoms enables the clinician to make the diagnosis.
MAS is a very serious, life-threatening complication of systemic JIA, which has to be treated with high dose corticosteroids, often in combination with cyclosporine. Even with this regimen the mortality rate is high.
Familial Haemophagocytic Lymphohistiocytosis (FHL), a congenital disease of childhood, is also characterised by haemophagocytosis. Recently, a defect in the perforin gene was found in patients with FHL. Because of the resemblance with MAS in systemic JIA, we have also investigated the perforin expression on cytotoxic CD8+ ve effector T-cells and NK-cells. We find a decreased expression of perforins in systemic JIA, which could play a role in the pathogenesis of the disease.
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