PRECORDIAL PAIN, LEUKOCYTOSIS AND BICYTOPENIA IN A TEENAGER WITH SYSTEMIC JUVENILE IDIOPATHIC ARTHRITIS UNDER IMMUNOSUPPRESSIVE THERAPY.

To highlight the importance of the new classification criteria for the macrophage activation syndrome (MAS) in systemic juvenile idiopathic arthritis in order to reduce morbidity and mortality outcome related to this disease.A 12-year-old female patient with diagnosis of systemic juvenile idiopathic arthritis under immunosuppression therapy for two years developed cough, acute precordial chest pain, tachypnea, tachycardia and hypoxemia for two days. Chest tomography showed bilateral laminar pleural effusion with bibasilar consolidation. The electrocardiogram was consistent with acute pericarditis and the echocardiogram showed no abnormalities. Laboratory exams revealed anemia, leukocytosis and increased erythrocyte sedimentation rate, as well as C-reactive protein rate and serum biomarkers indicative of myocardial injury. Systemic infection and/or active systemic juvenile idiopathic arthritis were considered. She was treated with antibiotics and glucocorticoids. However, 10 days later she developed active systemic disease (fever, evanescent rash and myopericarditis with signs of heart failure) associated with macrophage activation syndrome, according to the 2016 Classification Criteria for Macrophage Activation Syndrome in Systemic Juvenile Idiopathic Arthritis. She was treated for five days with pulse therapy, using glucocorticoids, immunoglobulin and cyclosporine A, with improvement of all clinical signs and laboratory tests.Myopericarditis with signs of heart failure associated with MAS is a rare clinical presentation of systemic juvenile idiopathic arthritis. Macrophage activation syndrome occurs mainly during periods of active systemic juvenile idiopathic arthritis and may be triggered by infection. Knowledge about this syndrome is crucial to reduce morbidity and mortality.