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PE21.5 | Juvenile Idiopathic Arthritis — SDL Guide (Part 2)

Complications: Uveitis and Macrophage Activation Syndrome

Two complications of JIA demand particular attention because they are treatable if detected early but catastrophic if missed: chronic anterior uveitis and macrophage activation syndrome (MAS).

Chronic Anterior Uveitis

Uveitis is the most important extra-articular complication of JIA, occurring in approximately 10–20% of all JIA cases but in up to 30% of oligoarticular ANA-positive patients. The critical clinical point — one that has cost many children their vision — is that JIA-associated uveitis is entirely asymptomatic in the majority of cases. There is no redness, no photophobia, and no blurred vision until the disease is advanced. By the time symptoms appear, the damage is done: band keratopathy (calcium deposits across the cornea), posterior synechiae (adhesions between the iris and lens), cataract, glaucoma, and ultimately blindness may have developed.

This is why routine, regular slit-lamp biomicroscopy is mandatory, not optional, for all JIA patients. Screening frequency is determined by risk stratification:
• Highest risk (oligoarticular or polyarticular JIA + ANA-positive + onset <6 years): slit-lamp every 3 months
• Intermediate risk: every 6 months
• Lowest risk (ERA, systemic JIA, RF-positive polyarticular): every 12 months (ERA and systemic JIA have a lower uveitis risk)

Treatment of active uveitis involves topical corticosteroids and mydriatics to prevent synechiae, with systemic methotrexate and biologics (adalimumab is particularly effective) for steroid-dependent or refractory cases.

Macrophage Activation Syndrome (MAS)

MAS is a life-threatening complication of systemic JIA, occurring in 10–15% of systemic JIA patients at some point in their disease course. It is a secondary haemophagocytic lymphohistiocytosis (HLH) — an uncontrolled activation of macrophages and T lymphocytes driven by excess IL-1β and interferon-gamma.

Clinically, MAS presents as sudden clinical deterioration in a child with systemic JIA: high unremitting fever, hepatosplenomegaly, lymphadenopathy, and a bleeding tendency (petechiae, mucosal bleeding). The paradoxical laboratory hallmark is falling ESR (because fibrinogen — an acute-phase reactant — is consumed by phagocytosis) alongside rising ferritin (often >500 ng/mL; in severe MAS may exceed 10,000 ng/mL). Cytopenias (falling WBC, haemoglobin, and platelet count despite active inflammation) and elevated liver enzymes round out the picture. Bone marrow biopsy shows haemophagocytosis — macrophages engulfing red cells, white cells, and platelets.

MAS is a haematological emergency. Treatment involves high-dose corticosteroids, cyclosporin A, and increasingly anakinra (IL-1 inhibitor) or etoposide in refractory cases.

Diagnosis and Investigation of JIA

JIA is a clinical diagnosis of exclusion — there is no single diagnostic test that confirms it, and no biomarker that is both sensitive and specific. The diagnosis is made when a child meets the ILAR criteria (arthritis onset <16 years, duration ≥6 weeks) AND other identifiable causes of childhood arthritis have been systematically excluded. This exclusionary approach is non-negotiable: infections, malignancies, and other connective tissue diseases can all mimic JIA, and initiating immunosuppression before excluding these is dangerous.

History and Examination
Key clinical clues: age at onset, number and distribution of affected joints, presence of systemic features (fever pattern — is it quotidian?), rash, family history of psoriasis or inflammatory bowel disease (for ERA/psoriatic), enthesitis (heel pain, plantar fasciitis), uveitis symptoms, and history of recent infection.

Investigations — Routine

Investigation	Purpose	Interpretation in JIA
Full blood count (CBC)	Rule out leukaemia; assess anaemia	Normocytic anaemia of chronic disease; thrombocytosis (reactive); leucocytosis in systemic JIA
ESR and CRP	Disease activity markers	Elevated in systemic > polyarticular > oligoarticular
ANA (antinuclear antibody)	Risk-stratify uveitis	Positive in 70–80% oligoarticular; NOT diagnostic of JIA
Rheumatoid Factor (RF)	Subtype polyarticular	RF+ on two occasions ≥3 months apart = RF-positive subtype
HLA-B27	Support ERA diagnosis	Positive in ~80% ERA; NOT diagnostic alone
Anti-CCP antibodies	RF-positive subtype	More specific than RF for polyarticular RF+ subtype
Synovial fluid analysis	Rule out septic arthritis	JIA: inflammatory (WBC 5,000–80,000), sterile; septic: WBC >100,000, bacteria
X-ray of affected joints	Baseline; assess erosions	Early: periarticular osteoporosis, soft-tissue swelling; late: joint space narrowing, erosions
MRI joints	Sensitive for early synovitis	Detects synovial enhancement, effusion, early cartilage loss before X-ray changes
Slit-lamp examination	Screen for uveitis	Must be performed at diagnosis and on scheduled intervals regardless of symptoms

Investigations to Exclude Other Diagnoses

Leukaemia must be actively excluded: if the child has bone pain (rather than joint swelling), night sweats, anaemia disproportionate to inflammation, or thrombocytopenia, perform peripheral blood smear and bone marrow biopsy before starting any immunosuppression. Do NOT mistake leukaemic arthralgia for JIA.

Septic arthritis: if any single hot, acutely tender joint is present with high fever and elevated inflammatory markers, joint aspiration and blood culture must precede any anti-inflammatory treatment.

Reactive arthritis: documented preceding infection, HLA-B27 status, and typically self-limiting course within 6 weeks distinguishes it from JIA.

Diagnostic approach summary:
1. Clinical diagnosis (ILAR criteria met)
2. Baseline bloods: CBC, ESR, CRP, ANA, RF, HLA-B27 if ERA suspected
3. Imaging: X-ray baseline; MRI for early/unclear cases
4. Slit-lamp: at diagnosis, then per risk-stratified schedule
5. Exclude infection (blood culture, joint aspiration if indicated) and malignancy

Management: NSAIDs, DMARDs, and Biologics

The management of JIA follows a stepwise, subtype-guided approach with the primary goals of suppressing inflammation, preserving joint function, preventing complications (particularly uveitis-related blindness and growth failure), and allowing the child to participate in normal childhood activities. Modern treatment with early aggressive therapy has transformed the outlook — most children achieve remission or low disease activity.

Step 1 — NSAIDs (Non-Steroidal Anti-Inflammatory Drugs)

NSAIDs are the first-line agents for pain and stiffness in mild oligoarticular disease. Naproxen (10–20 mg/kg/day in two divided doses) and ibuprofen (30–40 mg/kg/day in three to four divided doses) are the most used in paediatric practice. Naproxen has been associated with naproxen-induced pseudoporphyria (photosensitive skin fragility) in fair-skinned children — an important side effect to know. NSAIDs provide symptomatic relief but do NOT prevent joint erosions or uveitis; they are a bridge, not a disease-modifying treatment.

Step 2 — Intra-articular Corticosteroids (IACS)

Triamcinolone hexacetonide intra-articular injection is highly effective for oligoarticular JIA with 1–2 affected joints and is a standard treatment at this step. A single injection can provide disease control for months. Triamcinolone hexacetonide is preferred over triamcinolone acetonide due to its longer duration. Systemic corticosteroids are used judiciously — short courses for bridging or systemic JIA flares — but long-term oral steroids are avoided because of growth suppression, osteoporosis, cushingoid effects, and cataract.

Step 3 — Conventional DMARDs (Disease-Modifying Antirheumatic Drugs)

Methotrexate (MTX) is the anchor DMARD and the most widely used disease-modifying agent in JIA. It is indicated when NSAIDs alone are insufficient (extended oligoarticular, polyarticular, or uveitis not responding to topical therapy). Dosage: 10–15 mg/m²/week (oral or subcutaneous), with folic acid supplementation (1 mg/day) to reduce mucosal and hepatic side effects. Clinical response typically requires 4–6 weeks, with maximal benefit at 3–6 months. Monitoring: CBC, LFTs regularly. MTX is also effective for JIA-associated uveitis, particularly when combined with biologics.

Other conventional DMARDs sometimes used include leflunomide and sulfasalazine (particularly for ERA).

Step 4 — Biologics

Biologics are indicated when conventional DMARDs fail or in high-risk/severe disease:

• TNF-α inhibitors — Etanercept (TNF receptor fusion protein) and adalimumab (monoclonal anti-TNF antibody) are the most established biologics in JIA. Adalimumab is particularly effective for JIA-associated uveitis. Both are approved for polyarticular and oligoarticular JIA refractory to MTX. Screening for tuberculosis (TST/IGRA) is mandatory before starting any biologic due to reactivation risk.

• IL-6 inhibitor — Tocilizumab: approved for systemic JIA and polyarticular JIA. Highly effective for systemic features and MAS prevention in systemic JIA.

• IL-1 inhibitors — Anakinra and Canakinumab: canakinumab is approved for systemic JIA; anakinra for MAS acute management. These target the IL-1β pathway that is central to systemic JIA pathogenesis.

• CTLA4-Ig — Abatacept: a co-stimulation blocker that prevents T-cell activation; approved for polyarticular JIA refractory to other biologics.

Step-up Treatment Pyramid for JIA

Ophthalmology Monitoring — Non-Negotiable

All JIA patients must be enrolled in ophthalmology surveillance regardless of whether they have eye symptoms. Frequency depends on risk stratification (see Complications section). Slit-lamp examination is the standard; ophthalmoscopy does not detect anterior uveitis.

Physiotherapy and Rehabilitation

Physiotherapy is an essential and often underemphasised component: range-of-motion exercises maintain joint flexibility, muscle strengthening prevents atrophy, and hydrotherapy is particularly well tolerated in children. Occupational therapy assists with school aids and daily activities. Splinting may correct or prevent joint deformities.

Monitoring of Disease Activity

The ACR/PRINTO paediatric response criteria (Paediatric ACR 30/50/70) define clinical improvement as ≥30%/50%/70% improvement across a core set of variables: physician global, parent/patient global, number of active joints, joints with limited range of motion, ESR/CRP, and functional ability. These thresholds guide treatment escalation decisions.

Self-Assessment

Use the following case scenario to test your integrated understanding of JIA across all five arc steps: clinical presentation and subtype recognition, pathophysiology, investigation, management, and complication surveillance. Work through each question systematically before reading the model answers. Self-directed clinical reasoning — not passive recall — is the goal of this section.

Case: A 6-year-old girl is referred with a 5-month history of swelling and stiffness in her right knee and left ankle. Morning stiffness lasts about 45 minutes. There is no fever. Examination confirms warm, non-tender joint effusions bilaterally. No rash, no lymphadenopathy, no hepatosplenomegaly. Blood results: CBC — mild normocytic anaemia (Hb 10.8 g/dL); ESR 42 mm/h; CRP 18 mg/L; ANA 1:160 (positive); RF negative; HLA-B27 negative. X-rays show periarticular soft-tissue swelling with no erosions.

Questions to work through:

1. Identify the subtype. She has arthritis for >6 weeks, onset <16 years, 2 joints (≤4 in first 6 months), ANA-positive, RF-negative, HLA-B27 negative, no systemic features. → This is oligoarticular JIA, persistent subtype.

1. What is the single most important next investigation and why? → Slit-lamp ophthalmology examination. ANA-positive oligoarticular JIA with onset before age 7 is the highest-risk category for chronic anterior uveitis. The examination is mandatory at diagnosis and then every 3 months, regardless of the absence of eye symptoms.

1. Outline initial management. → NSAIDs (naproxen or ibuprofen, weight-based dosing) for symptomatic relief + intra-articular triamcinolone hexacetonide to both affected joints. If inadequate response at 4–6 months, escalate to methotrexate (10–15 mg/m²/week with folic acid).

1. What complication would change your management urgently? → Active uveitis on slit-lamp examination. Requires topical corticosteroids + mydriatics acutely; if persistent/refractory, add systemic methotrexate ± adalimumab.

1. What growth-related complication might develop if this knee remains inflamed for years? → Leg length discrepancy — chronic hyperaemia from knee synovitis accelerates growth plate activity on the affected side, causing overgrowth of the inflamed limb. Conversely, systemic inflammation and steroid use can cause generalised growth failure.

1. Name two systemic JIA-specific complications not present in this case. → (a) Macrophage activation syndrome (MAS) — falling ESR, rising ferritin, cytopenias, haemophagocytosis; (b) Serositis (pericarditis, pleuritis) — a defining criterion for systemic JIA that requires systemic corticosteroids or IL-1 inhibitors.

Step-up Management of Juvenile Idiopathic Arthritis