Polyarticular juvenile idiopathic arthritis

Overview

Polyarticular JIA: arthritis in 5 or more joints in the first 6 months of illness, onset before age 16, persisting >6 weeks. Divided into RF-positive and RF-negative subtypes with different prognoses.

Classification

RF-positive vs RF-negative polyarticular JIA

Feature	RF-positive	RF-negative
Age of onset	Older children/adolescents (9-16 yrs)	Broad distribution; early childhood and adolescence
Sex	Female predominance 3:1	Female predominance
HLA association	HLA-DR4 (mirrors adult RA)	No strong single HLA link
ANA positivity	Less common	~25-40%; increases uveitis risk
Joint pattern	Small joints hands/feet; erosive	Variable
Prognosis	Worst - majority persist into adult RA	~40-50% achieve remission

Presentation

•Morning stiffness >30-60 minutes - improves with activity (hallmark of inflammatory disease)

•Joint swelling - warm, synovial thickening; small joints hands/feet classic in RF-positive disease

•Limp or reduced mobility - often the presenting complaint in younger children

•Fatigue, anorexia, low-grade fever - cytokine-mediated; high-spiking fever suggests systemic JIA instead

•Cervical spine involvement - C2-C3 apophyseal joints; reduced neck movement

•Uveitis is asymptomatic - no red eye or pain; only detectable on slit-lamp examination

🚨

A child with JIA can have serious, sight-threatening uveitis with no eye symptoms whatsoever. Never reassure parents that the eyes are fine because the child is not complaining - slit-lamp examination is the only way to detect it.

Investigations

•Rheumatoid factor (RF) - must be positive on two occasions at least 3 months apart; predicts erosive disease

•ANA - positive in ~25-40% RF-negative disease; positive ANA increases uveitis risk and determines screening interval

•ESR and CRP - raised in active disease; useful for monitoring

•FBC - anaemia of chronic disease (normochromic normocytic), reactive thrombocytosis, leukocytosis

•Plain radiographs - periarticular osteopenia, joint space narrowing, erosions in RF-positive disease

•Slit-lamp examination - mandatory at diagnosis and regular intervals in all JIA subtypes; only reliable method to detect asymptomatic anterior uveitis

•Anti-CCP antibodies - if RF-positive, confirms seropositive erosive disease

⚠️

Normal CRP with markedly elevated ESR in a child with bone pain and arthralgia should raise concern for leukaemia until proven otherwise - do not delay FBC and blood film.

Management

•First-line (symptom control): ibuprofen or naproxen (NSAIDs) - bridge while awaiting DMARD response; do not alter disease course

•First-line DMARD: methotrexate oral/subcutaneous 10-15 mg/m² once weekly - cornerstone treatment; co-prescribe folic acid; takes 6-12 weeks for full effect

•Intra-articular: triamcinolone acetonide - for individual persistently inflamed joints; performed under anaesthesia/sedation in children

•Second-line (biologic): etanercept or adalimumab (anti-TNF) - NICE approved for polyarticular JIA failing methotrexate at maximum tolerated dose for ≥3 months

•Second-line alternative: abatacept (CTLA4-Ig, T-cell co-stimulation blocker) - NICE approved if anti-TNF contraindicated

🥉 Third-line

•tocilizumab (IL-6 receptor antagonist) or baricitinib (JAK inhibitor) - refractory disease under specialist supervision

•Systemic corticosteroids - sparingly for severe flares/bridging only; prolonged use causes growth suppression, osteoporosis, Cushingoid features

💡

MDT approach is essential: paediatric rheumatologist, ophthalmology (uveitis screening), physiotherapy (range of movement), occupational therapy (splinting/function), and psychological support.

Follow-up

•Uveitis screening - ANA-positive, young onset, RF-negative children at highest risk; typically every 3-6 months; frequency reduces with increasing age and disease duration

•Methotrexate monitoring - FBC and liver function tests every 4-8 weeks on stable dose

•Growth and development - height, weight, pubertal development at each visit

•Planned transition to adult rheumatology in mid-to-late adolescence; RF-positive patients likely to have ongoing active disease

Complications

•Chronic anterior uveitis - most feared; asymptomatic; causes band keratopathy, cataract, glaucoma, permanent visual loss; ANA-positive RF-negative children at highest risk

•Joint destruction - erosive disease in RF-positive subtype; flexion contractures and subluxation

•Growth failure - local (leg length discrepancy) and systemic (chronic inflammation + corticosteroids)

•Macrophage activation syndrome (MAS) - life-threatening; cytopaenias, coagulopathy, very high ferritin, haemophagocytosis; more common in systemic JIA but can occur in polyarticular disease