Makindo Medical Notes

Related Subjects: | Monoarticular Arthritis | Polyarticular Arthritis | Seronegative Spondyloarthropathies | Ankylosing Spondylitis | Enteropathic Spondyloarthritis | Reactive Arthritis | Psoriatic Arthritis

🧒 Juvenile Idiopathic Arthritis (JIA) is the most common chronic rheumatic disease of childhood. Aspirin should be avoided in children <12 due to the risk of Reye’s syndrome ⚠️. Tumour necrosis factor (TNF) 🧬 is a key pro-inflammatory cytokine in JIA pathogenesis.

📖 About

• Accounts for ~10% of all chronic arthritis in children.
• Onset usually <16 years (often <5 years).
• Systemic form may mimic infection or malignancy.
• Adult-onset Still’s disease is the adult equivalent, but rare.

🧬 Aetiology

• Equal male:female in systemic type; other subtypes more female.
• Genetic predisposition – HLA associations.
• Environmental triggers (infections, stress, trauma) may unmask disease.
• Pathogenesis: imbalance of Th1 (IFN-γ) and Th17 (IL-17) cells + dysregulated innate immunity (IL-1, IL-6, TNF-α).

🔑 Definitions

• Oligoarthritis: ≤4 joints in first 6 months.
• Polyarthritis: ≥5 joints in first 6 months.
• Systemic JIA (sJIA): Autoinflammatory form with fever + rash + organ involvement.

🌈 Subtypes

• Oligoarthritis – 50–60%.
• RF+ polyarthritis – 11–28% (resembles adult RA).
• RF– polyarthritis – 2–7%.
• Systemic JIA: 🩸 High spiking fevers, salmon-pink rash, lymphadenopathy, hepatosplenomegaly, serositis.
• Psoriatic arthritis 🎨.
• Enthesitis-related arthritis 🦶 – HLA-B27 associated.
• Undifferentiated arthritis.

🤒 Classic Clinical Features (Systemic JIA)

• Daily high fevers (>39°C), often evening spikes 🌡️.
• Transient pink/salmon maculopapular rash 🌸.
• Arthralgia/arthritis (sometimes late feature).
• Other: lymphadenopathy, hepatosplenomegaly, myocarditis, pericarditis, pleurisy, dry eyes (uveitis risk).
• ~50% risk of chronic destructive arthritis long-term 🦴.

🔎 Investigations

• Bloods: ↑ ESR, ↑ CRP, ↑ ferritin 📈 (esp. systemic JIA).
• FBC: Anaemia of chronic disease, ↑ neutrophils, ↑ platelets.
• Autoantibodies usually negative (ANA, RF, HLA-B27). ⚠️ High RF or ANA positivity may point to alternative diagnoses.
• Imaging: – X-rays may be normal early. – 🖥️ Ultrasound: synovial thickening, effusion, tenosynovitis. – MRI: 🥇 gold standard – detects bone marrow oedema and erosions.

🩺 Differentials

• Oligoarthritis mimics: Reactive arthritis, toxic synovitis, septic arthritis, osteomyelitis, haemophilia, sickle cell, trauma/NAT, tumours.
• Polyarthritis mimics: SLE, MCTD, rheumatic fever, IBD-related arthritis, sarcoid, CRMO.
• Systemic mimics: Infections (mycoplasma, EBV, endocarditis), Kawasaki disease, PFAPA, malignancy (ALL, lymphoma), autoinflammatory syndromes.

⚠️ Complications

• Growth disturbance & leg-length discrepancy.
• Joint contractures & disability.
• Macrophage activation syndrome (MAS) – life-threatening cytokine storm 🛑.

💊 Management

• All suspected JIA → urgent referral to paediatric rheumatology 👩‍⚕️.
• NSAIDs for pain & stiffness (avoid aspirin in <12).
• Steroids (systemic or intra-articular) for acute flares or organ involvement.
• Methotrexate – cornerstone steroid-sparing agent.
• Biologics: Anti-TNF (etanercept, adalimumab), IL-1 (anakinra), IL-6 (tocilizumab) for refractory cases 🧬.
• Vaccination: Avoid live vaccines if immunosuppressed. Annual flu 💉 recommended.
• Monitor growth, eye health (uveitis risk), and bone health (steroids + inactivity risk).

📚 References

• BMJ Clinical Review: JIA
• ResearchGate – JIA

Case – Systemic Juvenile Idiopathic Arthritis (Still’s disease)

A 9-year-old presents with 2 weeks of daily quotidian fevers peaking late afternoon, an evanescent salmon-pink rash appearing with fever, migratory arthralgia now localising to both knees, and sore throat; exam shows hepatosplenomegaly and mild lymphadenopathy. Labs: markedly ↑CRP/ESR, neutrophilia, anaemia, thrombocytosis, and very high ferritin (low glycosylated fraction if tested); cultures negative; CXR normal. After excluding infection and malignancy, diagnose systemic JIA; screen vigilantly for macrophage activation syndrome (MAS) (cytopenias, rising ferritin with falling ESR, ↑ALT, ↑triglycerides). Management: start systemic glucocorticoids for control and escalate early to targeted therapy—IL-1 blockade (anakinra) or IL-6 blockade (tocilizumab)—with physiotherapy and bone/gastroprotection; involve paediatric rheumatology and monitor joints, growth, LFTs, and MAS red flags.