Diagnostic Criteria for Juvenile Idiopathic Arthritis
JIA is diagnosed when arthritis of unknown etiology begins before age 16 years, persists for at least 6 weeks, and other known conditions are excluded. 1, 2
Core Diagnostic Requirements
The fundamental diagnostic criteria established by the American College of Rheumatology require three essential elements 1, 2:
- Age criterion: Onset before 16 years of age 1, 3, 4, 5
- Duration criterion: Arthritis persisting for at least 6 weeks 1, 3, 4, 5
- Exclusion criterion: Other known causes of arthritis must be ruled out 1, 2, 4
Definition of Arthritis
Arthritis is defined as swelling within a joint, or limited range of motion with joint pain or tenderness, observed by a physician, and not due to primarily mechanical disorders or other identifiable causes 6.
ILAR Classification Categories
The International League of Associations for Rheumatology divides JIA into 7 mutually exclusive categories based on clinical presentation within the first 6 months of disease 1, 7:
1. Polyarticular JIA (RF-negative)
2. Polyarticular JIA (RF-positive)
- Affects 5 or more joints within the first 6 months 6, 1
- Rheumatoid factor positive on at least two occasions 3 months apart 6, 1
- Resembles adult rheumatoid arthritis 1
3. Oligoarticular JIA
- Affects 1-4 joints during the first 6 months 7
- Subdivided into persistent (≤4 joints throughout disease) and extended (>4 joints after first 6 months) 7
4. Systemic-onset JIA
- Arthritis with daily spiking fever for at least 2 weeks 1
- Accompanied by one or more of: evanescent rash, serositis, hepatosplenomegaly, or generalized lymphadenopathy 1
- Accounts for 10-20% of all JIA cases 1
5. Enthesitis-related arthritis
- Arthritis and enthesitis, or arthritis/enthesitis with at least two of: sacroiliac joint tenderness, inflammatory spinal pain, HLA-B27 positivity, family history of HLA-B27-associated disease, acute anterior uveitis, or onset in males >6 years 7
6. Psoriatic arthritis
- Arthritis with psoriasis, or arthritis with at least two of: dactylitis, nail pitting/onycholysis, or psoriasis in a first-degree relative 7
7. Undifferentiated arthritis
- Arthritis that does not fulfill criteria for any category or fulfills criteria for more than one category 7
Clinical Assessment Features
Laboratory Findings
- Elevated inflammatory markers (ESR, CRP) support the diagnosis 1
- Autoantibodies including rheumatoid factor and anti-cyclic citrullinated peptide antibodies can define RF-positive polyarthritis 1
- HLA-B27 is associated with enthesitis-related arthritis 1
- Antinuclear antibodies are commonly positive in oligoarticular JIA 7
Imaging Findings
- Early plain radiographs are usually normal 1
- When abnormalities are present, they may include soft-tissue swelling or joint effusion rather than erosive changes 1
- Ultrasound and MRI can improve diagnostic certainty by detecting joint inflammation and assessing extent of involvement 1, 3
Important Clinical Caveats
Operational definitions used in clinical practice and research may differ from strict ILAR criteria. For treatment purposes, patients are often grouped by clinical phenotypes (polyarthritis with ≥5 joints, sacroiliitis, enthesitis) rather than strict ILAR categories 6, 2. Clinical trials frequently use a broader polyarticular phenotype that includes RF-positive and RF-negative polyarthritis, extended oligoarthritis, and undifferentiated arthritis 6, 1.
The 6-week duration requirement distinguishes JIA from acute arthritides and reactive arthritis, which typically resolve within 1-4 weeks 1. Negative blood and stool cultures substantially lower the probability of infectious causes 1.