Macrophage activation syndrome in juvenile idiopathic arthritis

Macrophage activation syndrome (MAS) is a rare and potentially lethal complication of chronic rheumatic diseases of childhood, in particular of systemic‐onset juvenile idiopathic arthritis (s‐JIA), resulting from uncontrolled activation and proliferation of T lymphocytes and macrophages. The onset, acute and dramatic, may mimic a flare of the underlying disease or a severe sepsis. Diagnosis is difficult and, until now, no specific criteria have been developed. Laboratory data show pancytopenia, coagulopathy, low ESR and low concentrations of serum albumin, and high levels of ferritin, liver enzymes and triglycerides. Activated macrophages are found in various organs, particularly in bone marrow. Most hypotheses on the mechanism underlying MAS are based on the data obtained in primary haemophagocytic lymphohistiocytosis (HLH), a genetic disease very similar to MAS. Prompt diagnosis is essential because prognosis is highly related to early treatment. The first approach was to use intravenous methylprednisolone pulse therapy; cyclosporin A was proposed in patients resistant to steroids. We describe nine patients affected by haemophagocytosis: seven patients developed MAS and two patients developed HLH. A child with s‐JIA developed three episodes of MAS. After the third episode, as there was no improvement with pulses of methylprednisolone and cyclosporine, he was successfully given etanercept. Conclusion: Our data, together with a similar, published observation, suggest that the TNF inhibitor etanercept is potentially useful for obtaining remission in children not responding to steroids and cyclosporin A.