Key Facts

Juvenile idiopathic arthritis (JIA) is the most common chronic inflammatory arthritis of childhood. It is a heterogeneous group of conditions classified by pattern of joint involvement and systemic features.

Epidemiology

• Prevalence: ~1 per 1,000 children in the UK
• Incidence: ~10 per 100,000 children per year
• Female predominance in oligoarticular and polyarticular (RF-negative)
• Male predominance in enthesitis-related arthritis
• Peak onset varies by subtype: oligoarticular 2–4 years; systemic any childhood age

ILAR Classification

1. Oligoarticular (≤4 joints): ~50%; persistent or extended
2. Polyarticular RF-negative (≥5 joints): ~20%
3. Polyarticular RF-positive (≥5 joints): ~5% (similar to adult RA)
4. Systemic (Still disease): ~10%
5. Enthesitis-related arthritis: ~10% (juvenile spondyloarthropathy, HLA-B27)
6. Psoriatic arthritis: ~5%
7. Undifferentiated: does not fit or fits >1 category

Pathophysiology

• Autoimmune synovitis → synovial hypertrophy → pannus formation → cartilage/bone damage
• Oligoarticular: likely innate immune dysregulation; ANA positive
• Systemic JIA: autoinflammatory (innate immune; IL-1 and IL-6 driven)
• Enthesitis-related: HLA-B27 associated, similar to adult spondyloarthropathy

Oligoarticular (Most Common)

• ≤4 joints; asymmetric large joints (knee, ankle)
• Young girl, ANA positive
• Often painless swelling noticed by parents
• HIGH RISK of anterior uveitis (asymptomatic — screen with slit lamp)

Polyarticular

• ≥5 joints; may be symmetric
• Small + large joints (hands, wrists, knees)
• RF-positive: similar to adult RA; aggressive
• RF-negative: variable

Systemic JIA (Still Disease)

• Quotidian (daily spiking) fever ≥2 weeks (spike to ≥39°C, returns to normal)
• Salmon-pink evanescent macular rash (with fever)
• Hepatosplenomegaly, lymphadenopathy, serositis (pericarditis, pleuritis)
• Arthritis may be delayed weeks–months after systemic features
• Risk of macrophage activation syndrome (MAS)

Enthesitis-Related Arthritis

• Older boys, HLA-B27 positive
• Lower limb arthritis + enthesitis (Achilles, plantar fascia)
• May progress to ankylosing spondylitis

Red Flags

• Systemic features without clear arthritis (wide differential — leukaemia, infection, malignancy)
• Rapid clinical deterioration in systemic JIA (MAS: falling ESR paradoxically + rising ferritin >10,000 + pancytopenia + coagulopathy)
• Asymptomatic uveitis → vision loss if not screened

Bloods

• FBC: anaemia (chronic disease), thrombocytosis; leucocytosis in systemic JIA
• ESR/CRP: elevated in active disease
• ANA: positive in ~70% oligoarticular (uveitis risk marker)
• RF: positive in ~5% polyarticular (RF-positive subtype)
• Anti-CCP: if RF-positive polyarticular
• Ferritin: markedly elevated in systemic JIA; very high (>10,000) in MAS
• LDH, fibrinogen, triglycerides: MAS screening

Imaging

• USS: synovitis, effusion
• MRI: gold standard for synovitis, bone marrow oedema, early erosions
• X-ray: soft tissue swelling (early), joint space narrowing, erosions (late)

Special Tests

• Slit lamp examination: uveitis screening (ophthalmology) — essential for ANA-positive patients
• Echocardiography: systemic JIA (pericarditis)
• Bone marrow aspirate: if systemic features without clear arthritis (exclude leukaemia)

Non-pharmacological

• Physiotherapy: joint protection, strengthening, ROM
• Occupational therapy: splints, aids
• Psychological support: chronic disease in childhood

Pharmacological

All subtypes:

• NSAIDs: naproxen 10–15mg/kg/day in 2 divided doses; ibuprofen
• Intra-articular corticosteroid: triamcinolone hexacetonide (first-line for oligoarticular; USS-guided)

Polyarticular/extended oligoarticular:

• Methotrexate 10–15mg/m²/week (oral or SC): first-line DMARD
• Anti-TNF (etanercept, adalimumab): if methotrexate insufficient/intolerant
• Abatacept (anti-CTLA-4): alternative biologic

Systemic JIA:

• Anakinra (anti-IL-1) or Canakinumab (anti-IL-1β): targeted first-line biologic
• Tocilizumab (anti-IL-6): very effective for systemic JIA
• Corticosteroids: bridge therapy (avoid long-term in children — growth implications)

MAS (emergency):

• High-dose IV methylprednisolone
• Ciclosporin
• Anakinra
• Supportive care (may need ITU)

Uveitis:

• Topical corticosteroid drops
• Methotrexate (steroid-sparing)
• Adalimumab (if refractory)

Referral Criteria

• Paediatric rheumatology: all suspected JIA (within 6 weeks of presentation — NHS standard)
• Ophthalmology: uveitis screening for all JIA (especially ANA positive)
• Physiotherapy/OT: all patients

• Oligoarticular: best prognosis; ~50% achieve remission off medication
• ~30% of oligoarticular extend to polyarticular (extended oligoarticular) — worse outcomes
• RF-positive polyarticular: worst joint prognosis; resembles adult RA
• Systemic JIA: variable; MAS mortality ~8–10%
• Uveitis: can cause band keratopathy, cataracts, glaucoma, visual loss if untreated
• Long-term: ~50–70% of JIA patients have active disease into adulthood
• Growth: chronic inflammation and steroids may impair linear growth
• Biologics have transformed outcomes — many children now achieve clinical remission

JIA Subtypes Summary