Workup of Juvenile Idiopathic Arthritis
The diagnostic workup for juvenile idiopathic arthritis (JIA) requires exclusion of other known causes of arthritis, confirmation of symptoms lasting at least 6 weeks, and onset before age 16 years. 1
Definition and Classification
JIA is defined as:
- Arthritis of unknown etiology
- Onset before 16 years of age
- Persistence of symptoms for at least 6 weeks
- Exclusion of other known conditions
JIA encompasses several disease subtypes according to the International League of Associations for Rheumatology (ILAR) classification 2, 1:
- Polyarticular (RF positive or negative)
- Oligoarticular (extended or persistent)
- Systemic
- Enthesitis-related arthritis
- Psoriatic arthritis
- Undifferentiated arthritis
Diagnostic Workup Algorithm
1. Clinical Assessment
- Joint examination: Document number and pattern of affected joints
- Assess for extra-articular manifestations:
- Fever patterns (especially quotidian fever in systemic JIA)
- Rash (evanescent, salmon-colored rash in systemic JIA)
- Eye symptoms (screen for uveitis)
- Enthesitis (tendon insertion inflammation)
- Sacroiliitis symptoms (inflammatory back pain)
2. Laboratory Investigations
Basic inflammatory markers:
- Erythrocyte sedimentation rate (ESR)
- C-reactive protein (CRP)
- Complete blood count (CBC) with differential
Immunologic markers:
Exclusionary tests (to rule out other conditions):
- Lyme serology (in endemic areas)
- Streptococcal antibodies (to rule out post-streptococcal reactive arthritis)
- Uric acid (to exclude gout)
- Liver and kidney function tests
3. Imaging Studies
Plain radiographs of affected joints:
- To assess for joint damage and establish baseline
- May show soft tissue swelling, joint space narrowing, or erosions in advanced cases
Ultrasound:
- Detects synovitis, effusions, and tenosynovitis
- Particularly useful for early disease detection
MRI:
- Gold standard for detecting early inflammatory changes
- Essential for evaluating sacroiliitis in enthesitis-related arthritis 2
- Shows bone marrow edema, synovitis, and cartilage damage
4. Ophthalmologic Evaluation
- Slit-lamp examination:
- Mandatory for all JIA patients to screen for uveitis
- Frequency based on risk factors (higher in young females with oligoarticular JIA and positive ANA)
5. Other Assessments
Functional assessment:
- Childhood Health Assessment Questionnaire (CHAQ)
- Clinical Juvenile Arthritis Disease Activity Score (cJADAS-10) 2
Growth and development monitoring:
- Height, weight, and pubertal development
- Bone age assessment if growth concerns
Disease Activity Assessment
The Clinical Juvenile Arthritis Disease Activity Score based on 10 joints (cJADAS-10) is recommended for categorizing disease activity 2:
- Low disease activity: cJADAS-10 ≤ 2.5 with ≥ 1 active joint
- Moderate/high disease activity: cJADAS-10 > 2.5
Special Considerations by Subtype
Polyarticular JIA
- Focus on RF and anti-CCP status
- Assess for risk factors: positive RF, positive anti-CCP, joint damage 2
Enthesitis-related JIA
- Evaluate for sacroiliitis with MRI
- HLA-B27 testing
- Assess for inflammatory back pain 2
Systemic JIA
- Monitor for macrophage activation syndrome (MAS)
- Assess for systemic features (fever, rash, serositis) 4
Pitfalls and Caveats
- Delayed diagnosis can lead to joint damage and impaired skeletal maturation 1
- No single diagnostic test exists for JIA; diagnosis is clinical and requires exclusion of other conditions
- Variable presentation - disease may develop over days or weeks, making initial diagnosis challenging 1
- Comorbidities should be assessed, including increased risk of cardiovascular disease and diabetes 3
- Immunosuppression from treatment increases infection risk 3
Early detection and prompt treatment are critical to prevent long-term complications and disability in children with JIA 1, 5.