DESCRIPTION

Juvenile idiopathic arthritis (JIA) is defined as chronic synovial inflammation of unknown etiology in at least one joint, for at least 6 weeks. Age of onset must be <16 years old. It is classified as one of seven subtypes:

• Oligoarticular JIA affects <5 joints during the first 6 months of the disease; tends to involve large joints, especially the knee. Peak age of onset is 1 to 3 years.
  • Persistent oligoarticular JIA remains in <5 joints after the 6th month of disease.
  • Extended oligoarticular JIA spreads to involve 5 or more joints (cumulatively) after the 6th month of disease; worse prognosis than persistent oligoarthritis
• Polyarticular JIA affects ≥5 joints. Biphasic peak ages of onset are 1 to 4 years and 9 to 14 years; divided into two subtypes:
  • Rheumatoid factor–positive (RF+) polyarticular JIA is the most similar to adult-onset rheumatoid arthritis (RA); often aggressive
  • Rheumatoid factor–negative (RF−) polyarticular JIA is usually less aggressive and easier to control.
• Systemic-onset JIA
  • Characterized by high spiking, quotidian (daily) or diquotidian (twice daily) fevers and an evanescent pink/salmon-colored macular rash
  • Affected children may also have lymphadenopathy, hepatosplenomegaly, pericarditis, or pleuritis.
  • Arthritis may not appear until weeks to months after the onset of the systemic symptoms.
  • Can occur at any age: The analogous disease in adults is Still disease.
  • ~10% of cases are complicated by life-threatening macrophage activation syndrome (MAS).
• Enthesitis-related arthritis (ERA)
  • Entheses (e.g., osteotendinous junctions, osteoligamentous junctions) are sites where tendons or ligaments attach to bone.
  • ERA has a male predominance, with typical onset in late childhood or adolescence.
  • Many are human leukocyte antigen (HLA)-B27 positive.
• Psoriatic arthritis
  • Associated with psoriasis, but often arthritis and psoriasis develop asynchronously.
  • Can be oligoarticular or polyarticular
  • Often involves small joints of hands and feet as well as knees
  • Dactylitis (inflammation of an entire digit with joint and tendon involvement) is seen in nearly 50% of patients.
  • Nail pitting and/or onycholysis are often seen.
• Undifferentiated arthritis is arthritis that does not fall into any of the other categories or falls into more than one of the above categories.

EPIDEMIOLOGY

• Affects >100,000 children in the United States
• Girls are affected twice as often as boys, but boys are affected more frequently with ERA.
• ~50% of children with JIA have the oligoarticular subtype; ~30% have the polyarticular subtype; ~10% have systemic-onset JIA.

RISK FACTORS