Description

• Juvenile idiopathic arthritis (JIA) is the most common chronic pediatric rheumatologic disease.
• JIA is associated with significant disability.
  • Age of onset: <16 years of age
  • Common symptoms: joint swelling, restricted range of motion, warmth, redness, pain
  • ≥6 weeks of symptoms prior to diagnosis
• Seven (International League of Associations for Rheumatology [ILAR]) subtypes determined by clinical characteristics in first 6 months of illness (1):
  • Systemic: 10%; preceded by febrile onset of ≥2 weeks with rash, serositis, hepatosplenomegaly, or lymphadenopathy (1)
  • Polyarticular rheumatoid factor (RF) (+): 2–7%; ≥5 joints involvement (1); large and small joints; RF positive on two tests ≥3 months apart (2)
  • Polyarticular RF (−): 10–30%; ≥5 (large and small) joints involved (1); RF negative (2)
  • Oligoarticular: 30–60%; involvement of 1 to 4 joints; risk for chronic uveitis in antinuclear antibodies (ANA) (+) females (1) and axial skeletal involvement in older boys (2). Types: (i) persistent (40%): knee, ankle, elbow; (ii) extended type (20%): >4 joints after first 6 months
  • Psoriatic arthritis: 5%; arthritis with psoriasis or arthritis with >2 of the following: dactylitis, nail changes (pitting), psoriasis in first-degree relative (1)
  • Enthesitis-related arthritis: 1–11%; arthritis and enthesitis or one of them plus at least two of the following: sacroiliac or lumbosacral pain, Reiter syndrome or acute anterior uveitis in first-degree relative, acute symptomatic anterior uveitis, human leukocyte antigen (HLA)-B27 (+), history of ankylosing spondylitis, sacroiliitis with inflammatory bowel disease, onset of arthritis in male >6 years old (1)[C]
  • Undifferentiated arthritis (11–21%): presents with overlapping symptoms in ≥2 categories above or arthritis that does not fulfill above categories (2)
• Systems affected: musculoskeletal, hematologic, lymphatic, immunologic, dermatologic, ophthalmologic, gastrointestinal
• Synonyms: juvenile chronic arthritis; juvenile arthritis; juvenile rheumatoid arthritis (JRA); Still disease (2)

Epidemiology

• Male = female (1); onset: throughout childhood; 54% of cases occur in children 0 to 5 years.
• Polyarticular RF (+): female > male, 3:1 (2); onset: late childhood or adolescence (1)
• Polyarticular RF (−): female > male, 3:1; onset: early peak, 2 to 4 years; late peak, 6 to 12 years (2)
• Oligoarticular: female > male, 5:1; onset: 2 to 4 years (2)
• Psoriatic: female > male, 1:0.95 (2); onset: early peak, 2 to 3 years; late peak, 10 to 12 years (1)
• Enthesitis: female > male; onset: early peak, 2 to 4 years; late peak, 6 to 12 years (2)
• Affected patients have an increased risk of developing cancer, although short-term risk is low.

Incidence
2 to 20/100,000 children <16 years in developed nations

Prevalence
16 to 150/100,000 children <16 years in developed nations (1)

Etiology and Pathophysiology

• Humoral and cellular immunodysregulation. T lymphocytes play a key role.
• Genetic predisposition; IL2RA/CD25 and VTCN1 implicated as genetic loci
• Environmental triggers, possibly infectious
  • Rubella or parvovirus B19 (3)
  • Heat shock proteins (3)
• Immunoglobulin or complement deficiency

• HLA class I (A, B, C) and II (DR, DP, DQ) alleles
• HLA-A2 = early onset oligoarthritis in females
• HLA class II increases risk of systemic and oligoarticular JIA.
• HLA-B27 increases risk of enthesitis-related arthritis.
• HLA-DR4 is associated with polyarthritis RF (+) (3)[C].

Risk Factors

Female gender 3:1

General Prevention

None identified

Commonly Associated Conditions

Other autoimmune disorders, chronic anterior uveitis (iridocyclitis), nutritional impairment, growth issues (3)[C]