Plasma exchange successfully treated macrophage activation syndrome in rheumatoid factor‐positive polyarticular juvenile idiopathic arthritis with co‐existing pneumonia

Macrophage activation syndrome (MAS) is one of the serious complications associated with rheumatic diseases, especially systemic juvenile idiopathic arthritis (sJIA). Here we describe a 9‐year‐old girl with rheumatoid factor (RF)‐positive polyarticular JIA, not sJIA, combined with pneumonia who was successfully treated by plasma exchange. She was diagnosed with RF‐positive polyarticular JIA based on positive RF and multiple joint swelling and tenderness 3 years ago. She was admitted in our hospital with myalgia for 2 days and a high fever for half a day. Physical examination revealed relapsing joints symptoms and rough breathing sounds of lungs. The laboratory examination showed increased liver enzymes, elevated serum ferritin and procalcitonin (PCT), decreased percentage of nature killer (NK) cells and fibrinogen, and activated macrophage phagocytosing hematopoietic elements in bone marrow. The elevated PCT and chest computed tomography scan confirmed she also had pneumonia. Intravenous methylprednisolone and oral cyclosporine A followed by intravenous immunoglobulin were added on the basis of antibiotics therapy, but clinical symptoms and laboratory findings did not improve. Finally, we changed to plasma exchange once every other day for a total of three times. Within 1 week, the girl recovered from the MAS completely.