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Juvenile idiopathic arthritis (JIA)
JIA is arthritis that starts before age 16 and lasts at least 6 weeks with no other cause; the commonest form is oligoarticular in a young ANA-positive girl, where the great danger is silent uveitis — so eyes are checked regularly with a slit lamp.
Why it matters in the exam
The classic question: a 3-year-old girl with a knee swollen for weeks, limping in the morning, generally well, ANA-positive — oligoarticular JIA. The important step is referral for an eye examination, because anterior uveitis in these children is painless and does not cause redness, and if undetected it causes blindness. First-line treatment is NSAIDs and intra-articular steroid injection (triamcinolone).
Systemic JIA is completely different: a "spiking" fever once or twice a day lasting two weeks or longer, a fleeting salmon-coloured rash that comes with the fever spikes, serositis, hepatosplenomegaly and lymphadenopathy. The dangerous complication is macrophage activation syndrome (MAS): the child worsens, platelets and ESR fall unexpectedly, ferritin rises sharply and fibrinogen falls. The systemic form is treated with IL-1 or IL-6 blockers.
In the polyarticular form (5 joints or more) treatment is methotrexate and then a biologic (TNF inhibitors). For the exam, remember the important differential diagnosis: septic arthritis (fever, one joint, non-weight-bearing), leukaemia (night pain, disproportionate pain, cytopenias or a high LDH) and reactive arthritis. Enthesitis-related JIA with HLA-B27 appears in boys over 6 with low back pain.
Key points
- JIA: arthritis before age 16, at least 6 weeks, with no other cause.
- The commonest form: oligoarticular in a young ANA-positive girl.
- Slit-lamp eye screening because of silent uveitis.
- Systemic: spiking fever, evanescent rash; the dangerous complication is MAS.
- Treatment: NSAIDs, joint injection, methotrexate, biologics.
Summary table
| Subtype | Features | Key complication | Treatment |
|---|---|---|---|
| Oligoarticular | 4 joints or fewer in the first 6 months; young girls; ANA-positive | Silent anterior uveitis | NSAIDs, intra-articular triamcinolone; methotrexate as needed |
| Polyarticular RF-negative | 5 joints or more, small and large joints | Functional limitation | Methotrexate, biologic |
| Polyarticular RF-positive | Adolescent girls, resembles adult RA | Joint destruction | Methotrexate and early biologic |
| Systemic | Spiking fever for two weeks, evanescent salmon rash, serositis, hepatosplenomegaly | MAS: very high ferritin, falling platelets and ESR | IL-1 or IL-6 blockers; steroids |
| Enthesitis-related | Boys over 6, HLA-B27, low back pain, enthesitis | Acute painful uveitis | NSAIDs, TNF inhibitors |
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Sources
- ACR/Arthritis Foundation Guideline for the Treatment of Juvenile Idiopathic Arthritis, 2019 (non-systemic polyarthritis, sacroiliitis, enthesitis) and 2021 (oligoarthritis, TMJ, systemic JIA) — Treatment recommendations
- ILAR classification of juvenile idiopathic arthritis (Edmonton revision), 2004 (in current use) — Subtypes
- Nelson Textbook of Pediatrics, 22nd edition (2024) — Juvenile Idiopathic Arthritis
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.