Juvenile idiopathic arthritis
- Lesion
Chronic arthritis that starts before 16 with no known cause. Several types exist; some damage the eyes silently.
What it is
Juvenile idiopathic arthritis is a group of chronic inflammatory arthritides that begin before the age of 16 and last at least six weeks without another cause. It differs from adult rheumatoid arthritis: large joints are more often affected than small ones, rheumatoid factor and nodules are usually absent, ANA is often positive and chronic anterior uveitis is common. The systemic form (Still disease) behaves like an autoinflammatory disease driven by IL-1 and IL-6, with quotidian fever and an evanescent salmon rash.
Structure
- Synovium: hyperplasia, lymphocytes and plasma cells, similar to adult RA but with less pannus erosion early.
- Erosions occur later and less often than in adult RA.
- Uveitis: lymphocytes and plasma cells in the iris and ciliary body; band keratopathy and cataract over time.
Step by step
- Genetic risk (HLA alleles, PTPN22) and possible infectious triggers start a T-cell–driven synovitis in most forms.
- Th1 and Th17 cells and cytokines inflame the synovium.
- In systemic JIA, innate cells (monocytes and neutrophils) overproduce IL-1, IL-6 and IL-18.
- Chronic inflammation near growing epiphyses disturbs growth.
- Uncontrolled systemic disease can spiral into macrophage activation syndrome.
Main subtypes of juvenile idiopathic arthritis
| Subtype | Joints | Features |
|---|---|---|
| Oligoarticular | Four or fewer, large (knee, ankle) | Young girls, ANA positive, uveitis risk |
| Polyarticular RF-negative | Five or more | Most common polyarticular form |
| Polyarticular RF-positive | Five or more, small joints | Adolescent girls; like adult RA |
| Systemic (Still disease) | Variable | Quotidian fever, salmon rash, serositis; IL-1 and IL-6 |
| Enthesitis-related | Lower limbs, sacroiliac | HLA-B27, boys over six |
| Psoriatic | Asymmetric, dactylitis | Psoriasis or family history |
Clinical notes
- Limping child with a swollen knee for weeks and morning stiffness: think of JIA once infection is excluded.
- Children with oligoarticular JIA need scheduled slit-lamp exams because uveitis is often painless.
- Systemic JIA can look like infection or leukaemia; marrow examination may be needed.
Test yourself
Think of the answer, then tap the question to see it.
Which subtype of JIA carries the highest risk of silent uveitis?
Oligoarticular JIA, especially ANA-positive young girls.
Which cytokines drive systemic JIA?
Mainly IL-1 and IL-6 (also IL-18).
How does JIA differ from adult RA?
More large-joint disease, usually no RF or nodules, often ANA positive, uveitis, and effects on growth.
What life-threatening complication can systemic JIA cause?
Macrophage activation syndrome.
Elsewhere in DurgiPedia
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Juvenile Arthritis | Still's Disease | JRA | MedlinePlus (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.