sJIA because acute lymphoblastic leukemia may cause joint pain and swelling, fever, lymphadenopathy, and HSM that are indistinguishable from findings in sJIA In a patient being treated for known sJIA, fever may represent recurrence of JIA, or it may be because of an intercurrent infection Fevers in sJIA typically follow the classic twice daily pattern, with two peaks above 39°C daily, as well as periods at or below normal without use of antipyretic medications If there are no localizing signs of infection, the CBC shows the leukocytosis, thrombocytosis, and anemia typical of JIA, and the urinalysis is normal, the child may be treated for a presumed JIA flare Notably, an acute infection can cause a flare of disease and both entities may coexist Children being treated with immunosuppressive medications may require empiric antibiotics or observation in the hospital until negative culture results allow infection to be excluded If the patient has received more than 20 mg of prednisone daily for more than weeks within the previous 12 months, appropriate coverage with stress doses of steroids (three times the physiologic dose) is indicated while the infection is being treated Fever in sJIA, especially within months of disease onset, occasionally may be caused by MAS, also known as reactive hemophagocytic lymphohistiocytosis (HLH) This spectrum of disease will be discussed in greater detail below This life-threatening complication is characterized by systemic inflammation with disseminated intravascular coagulopathy with diffuse microthromboses, cytopenias, hepatic inflammation, SIRS-type physiology, and CNS changes progressing to seizures or coma The cause of MAS is unknown, but it does occur more commonly during viral illnesses, as well as in children receiving NSAIDs or DMARDs (particularly sulfasalazine) as treatment A subset of children with sJIA likely have a genetic predisposition to MAS as they carry mutations in genes associated with HLH Differentiation from sepsis or a flare of JIA may be difficult, although a sudden rise in hepatic enzymes, ferritin, and triglycerides or a sudden drop in platelets, red blood cells, or ESR (due to consumption of cellular elements and fibrinogen) is suggestive Early diagnosis and a high level of suspicion are essential Treatment with anakinra, pulse-dose methylprednisolone (30 mg/kg, maximum g), and/or cyclosporine, as well as general support measures for DIC, often lead to full recovery Delayed diagnosis, in contrast, is accompanied by a reported mortality rate of 20% to 50% Cardiac Complications Cardiac involvement is an important feature of sJIA but is uncommon in other subtypes of juvenile arthritis Pericarditis, like other systemic manifestations of Still disease, most often occurs during the first years of the illness Fortunately, pericardial effusions in JIA rarely lead to cardiac tamponade Valvulitis is not typical of JIA and should suggest the possibility of acute rheumatic fever or bacterial endocarditis Myocarditis is rare but may be seen Bed rest and therapy with an NSAID should be adequate for the treatment of mild to moderate pericarditis due to JIA Corticosteroids (prednisone to mg/kg/day, maximum 60 to 80 mg) are indicated for the treatment of noninfectious myocarditis,