Systemic Juvenile Idiopathic Arthritis

A 5-year-old boy was referred to our hospital with high-grade intermittent fever for 7 days without localizing signs. He had been treated with a course of amoxicillin for 5 days outside with no response. His past medical history was uneventful. General physical examination showed no abnormalities, and systemic examination was normal. A diagnosis of probable enteric fever or viral infection was made, blood tests were sent, and he was started on antipyretics. On the following day, blood tests revealed a normal hemoglobin level and peripheral smear, a total leucocyte count of 17,600/cu mm with 72% polymorphs, a platelet count of 386,000/cu mm, and elevated C-reactive protein and erythrocyte sedimentation rate. Urine examination was normal. The diagnosis of a probable occult bacterial infection was made. The child was hospitalized for parenteral antibiotics and for further evaluation. Serological test results for dengue, scrub, and leptospirosis were negative. Chest X-ray and abdominal ultrasound were normal. Blood and urine cultures were sterile. High-grade intermittent fever continued with a maximum temperature of 106°F. On day 3 of hospitalization (day 11 of fever), he started complaining of generalized body pain, more in the knees during the episodes of fever. However, musculoskeletal examination revealed no signs of arthritis. Bone marrow aspiration culture, bone marrow biopsy, echocardiogram, and CT scans of the thorax and abdomen did not reveal any abnormality, and repeated blood cultures were sterile. During one of the fever spikes, a faint, reddish maculopapular rash was noted over his trunk. The possibility of a connective tissue disorder or an auto-inflammatory condition like systemic juvenile idiopathic arthritis (SJIA) was considered. Laboratory tests were negative for antinuclear antibodies and rheumatoid factor. Serum ferritin level was elevated (4350 ng/mL). Repeated clinical examination failed to demonstrate arthritis. In view of the inconclusive clinical picture, a fludeoxyglucose-18 (FDG) positron emission tomography (PET) scan/CT scan was performed, which showed mildly elevated uptake in both the knees, and ankles suggesting synovitis. The images also revealed elevated metabolic activity diffusely in the spleen, bone marrow, and some inguinal lymph nodes without signs of malignancy, suggesting SJIA. He was started on daily naproxen. A marked decrease in fever spikes, pain, and inflammatory markers was seen within 3 days. He was discharged with advise to follow-up with the pediatric rheumatology team.