General
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• Common connective tissue disease in children age 15 years or less - most common chronic rheumatic illness in children (Dermatology Online Journal 2001;7(2):19)
• Worldwide incidence varies from 0.008 to 0.226 per 1,000 children

Sites
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• Knees, wrists, elbows, ankles

Pathophysiology
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• Pathogenesis: oligoarthritis and polyarthritis group are T helper 1 cell mediated disorders; precise mechanisms are unclear, but proinflammatory cytokines are responsible for part of clinical symptoms (Korean J Pediatr 2010;53:921)

Diagrams
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Cytokine signaling pathways

Clinical features
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• 65% male
• Either oligoarticular (<5 joints), polyarticular (5 or more joints) or systemic
• Compared to classic rheumatoid arthritis, oligoarthritis is more common; systemic large joints are affected more than small joints
• Associated with HLA-DRB1, infections by mycobacteria, bacteria, viruses
• 70% recover, 10% have residual severe joint deformities
• Usually seronegative for rheumatoid factor
• Symptoms: systemic onset with fever, rash, hepatosplenomegaly, serositis; also warm and swollen joints; pericarditis, myocarditis, pulmonary fibrosis, glomerulonephritis, uveitis, growth retardation

Case reports
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• 4 year old girl with limping and swelling of knee (University of Hawaii 2003)
• 6 year old boy with knee and heel pain (Rev Med Inst Mex Seguro Soc 2006;44:355)
• 8 year old girl with knee pain (Arch Dis Child 2005;90:1038)
• 9 year old boy with painful swelling of knee and elbow joints (Bangladesh Journal of Child Health 2010;34:31)

Treatment
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• NSAIDs initially (Korean J Pediatr 2010;53:936)

Clinical images
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Flesh-colored, subcutaneous nodules

Swelling and flexion contracture

Polyarticular disease

Systemic onset disease

Micro description
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• Similar morphologic changes as adult rheumatoid arthritis but less severe

Micro images
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Degenerated fibrin with surrounding palisading histiocytes

Destruction of articular cartilage of femoral head

Proliferative and exudative synovitis

Typical pannus formation

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