Abstract
We encountered a case of systemic juvenile idiopathic arthritis（sJIA）with myocarditis． A 5-year-old
boy was admitted to a regional hospital after exhibiting prolonged fever，joint pain and skin rash． A diagnosis of sJIA was made． His condition did not improve despite therapy，and he was transferred to our hospital． On hospital day 2，severe chest pain developed． Electrocardiography showed ST elevations in leads V2-V6 and heart fatty acid binding protein test was positive． Echocardiography showed reducing left ventricular wall motion and mild mitral regurgitation． Multiple and regional defects in the left ventricular lateral wall and inferior wall and apex were detected by quantitative gated single photon emission computed tomography（QGS）． Myocarditis due to sJIA was diagnosed by QGS and therapy including administration of diuretics and a phosphodiesterase
inhibitor was started． Three days after starting therapy， chest pain improved． The multiple defects were improved by hospital day l3. Cardiac involvement is more frequent with sJIA than with other subtypes of JIA， and is the main cause of death among JIA patients． Faster diagnosis and therapy can contribute to better outcomes for sJIA patients with myocarditis．
