Description

• Most common chronic rheumatic illness in children and a significant cause of short- and long-term disability
• General characteristics:
  • Age of onset <16 years
  • Signs of arthritis: Joint swelling, limitation of motion, pain, heat, or tenderness
  • >6 weeks of symptoms
• 7 subtypes exist, according to the International League of Associations for Rheumatology, determined by clinical characteristics seen in first 6 months of illness (1):
  • Systemic (Still disease): 10–20%; usually characterized by febrile onset and evanescent rash with multiple physical and laboratory abnormalities
  • Polyarticular rheumatoid factor (RF) (+): 5–10%; multiple (≥5) joint involvement; large and small joints affected. RF positive 2× on tests at least 3 months apart.
  • Polyarticular RhF (–): 30%; ≥5 joint involvement, large and small joints affected; RF negative
  • Oligoarticular: 40–50%; involvement of ≤4 joints, usually larger joints, especially of lower extremities; risk for chronic uveitis in young girls and axial skeletal involvement in older boys
  • Psoriatic arthritis: 2–15%; arthritis with psoriasis or arthritis with at least 2 of following: Dactylitis, nail pitting or onycholysis, psoriasis in 1st-degree relative
  • Enthesitis arthritis: 1–7%; includes ankylosing spondylitis and inflammatory bowel disease–related arthritis. Peripheral and axial involvement.
  • Undifferentiated arthritis: Arthritis that does not fulfill above categories or fills ≥2 categories
• System(s) affected: Hematologic/Lymphatic/Immunologic; Musculoskeletal
• Synonym(s): Juvenile chronic arthritis; Juvenile arthritis; Juvenile rheumatoid arthritis (JRA); Still disease

Epidemiology

• Systemic: Girls = Boys; onset is throughout childhood (2)
• Polyarticular RF (+): Girls > Boys 3:1; age of onset late childhood or adolescence (2)
• Polyarticular (–): Girls > Boys 3:1; age of onset early peak 2–4 years and late peak 6–12 years
• Oligoarticular: Girls > Boys 5:1; age of onset peak 2–4 years (2)
• Psoriatic: Girls > Boys 1:0.95; age of onset late childhood or adolescence (2)
• Enthesitis: Girls < Boys 1:7; age of onset early peak 2–4 years and late peak 6–12 years (2)
• Affected patients have and increased risk of developing cancer, although short-term risk is found to be low (3,4).

Incidence
1–22 per 100,000 children <16 years per year

Prevalence
8–150 per 100,000 children <16 years

Risk Factors

• Certain human leukocyte antigen (HLA) class I and II alleles
• HLA-A2 in early-onset oligoarthritis in girls
• HLA-DRB1^*11 confers increased risk of systemic and oligo-JIA.
• HLA-B27 risk of enthesitis-related arthritis
• HLA-DR4 associated with RF (+) polyarticular disease

General Prevention

No known preventive measures

Etiology

Multifactorial, including:

• Immunodysregulation
• Genetic predisposition
• Environmental triggers, possibly infectious:
  • Rubella or parvovirus B19 (5)
  • Heat shock proteins (5)
• Immunoglobulin or complement deficiency

Commonly Associated Conditions

Other autoimmune disorders, chronic anterior uveitis (iridocyclitis), nutritional impairment, growth disturbances (5)