Juvenile idiopathic arthritis (JIA; formerly called juvenile rheumatoid arthritis) is a broad term for childhood rheumatic diseases that begin before the age of 16 and are characterized by joint inflammation that lasts more than 6 weeks. It is classified into various types based on the pattern of joint involvement, the presence of extra-articular manifestations (e.g., uveitis, rash, nail changes, lymphadenopathy, hepatosplenomegaly), laboratory findings, and disease prognosis. Oligoarticular JIA, which is the most common type, presents with asymmetric involvement of up to four joints (with the knee joint most often affected). Nearly half of all cases of oligoarticular JIA are associated with anterior uveitis, which may be diagnosed by . Laboratory tests such as ESR, rheumatoid factor (RF), antinuclear antibodies (ANA), and the HLA-B27 antigen test are used to classify and determine the prognosis of JIA. Treatment of JIA is similar to that of adult rheumatoid arthritis and involves the use of NSAIDs, intra-articular steroid injections, and (DMARDs) such as methotrexate. Systemic glucocorticoid therapy should be avoided because of the risk of growth impairment.
Epidemiological data refers to the US, unless otherwise specified.
- Immunological predisposition: different HLA associations 
- Possibly triggered by a viral or bacterial infection
- Exposure to antibiotics during childhood may increase the risk of JIA.
Autoimmune and/or autoinflammatory disease → chronic synovial inflammation with infiltration of plasma cells, B lymphocytes, and T lymphocytes → joint capsule hyperplasia → growth of fibrovascular connective tissue (pannus) → invasion of the articular surface → loss of joint function 
For the exact pattern of joint involvement and specific extra-articular symptoms, see “Subtypes and variants” below.
- Arthritic symptoms
- Extra-articular manifestations 
- Nonspecific features
Subtypes and variants
|Classification of juvenile idiopathic arthritis |
|Type of JIA|| |
|Peak incidence||Sex||Definition||Pattern of joint involvement|| |
| || || || |
Seronegative polyarticular JIA 
| || || || || |
|Seropositive polyarticular JIA || || || || || |
|Systemic JIA (Still disease)|| || || |
A prerequisite for the diagnosis of all forms of JIA is that arthritic symptoms begin before the age of 16 and last ≥ 6 weeks.
The clinical diagnosis of JIA can be supported by a number of diagnostic tests.
Blood tests are used to classify JIA, assess the prognosis, and rule out other similar conditions (see “Subtypes and variants” above).
Autoantibodies levels 
Rheumatoid factor (RF)
- Absent in most cases of JIA (except seropositive polyarticular JIA)
- Associated with poor prognosis
- ↑ ANA
- Anti-CCP antibodies: indicate a poor prognosis 
- Rheumatoid factor (RF)
- Acute phase reactants
- Ultrasound 
- May be used for the identification of JIA complications
- Should not be performed routinely
Other diagnostic tests
- Synovial biopsy
- Slit lamp examination: : should be performed for regular ophthalmological screening in patients with anterior uveitis 
Anterior uveitis that occurs with JIA may be asymptomatic (especially in the case of chronic anterior uveitis). However, untreated anterior uveitis is associated with a high risk of developing glaucoma, cataracts, and optic nerve damage. Therefore, early detection via slit lamp examination and swift initiation of treatment are of paramount importance.
The differential diagnosis of JIA includes other causes of nonsuppurative arthritis in children: 
- Acute lymphocytic leukemia
- Connective tissue disease (e.g., SLE, Sjögren syndrome)
The differential diagnoses listed here are not exhaustive.
First-line therapy 
- Local intra-articular steroids (e.g., ): indicated in the case of active arthritis
- Disease-modifying antirheumatic drugs (DMARDs) 
- Biologic agents
Systemic glucocorticoid therapy (oral, IV) 
- Rarely used in children because of the risk of catabolic side effects (e.g., osteoporosis, growth impairment)
- A short course of systemic glucocorticoid therapy may be prescribed in the following situations:
- Physiotherapy: to prevent joint deformities
- Surgery, splints, and/or orthotics: to correct limb length discrepancy and/or joint deformities
Most drugs that are used to treat adult rheumatoid arthritis may be used to treat JIA as well (see “Therapy” in “ ”). However, certain forms of therapy (e.g., systemic glucocorticoid therapy) should, as a rule, be avoided in children.
- Articular complications
- Chronic anterior uveitis → blindness
- Pericarditis, pleuritis
Macrophage activation syndrome (MAS) 
- A rare complication of JIA (most commonly systemic JIA) characterized by thrombocytopenia, elevated transaminases, low fibrinogen, and markedly increased ferritin levels
- In a patient with systemic JIA, the presence of a normal or decreased WBC count, falling ESR, and/or increased triglyceride levels should raise the suspicion of MAS.
We list the most important complications. The selection is not exhaustive.
The clinical course and prognosis are highly variable (see “Subtypes and variants” above) . Most cases (∼ 95%) resolve by puberty.
Factors associated with a poor prognosis 
- Early onset
- Prolonged active systemic disease
- Hip and/or wrist involvement
- Polyarticular involvement
- Symmetrical disease
- Presence of RF
- Presence of
Early disease onset is associated with a greater degree of growth impairment and deformity.