Juvenile Idiopathic Arthritis (JIA)
Juvenile idiopathic arthritis (JIA) is an umbrella term for inflammatory arthritis of unknown cause that lasts for at least 6 weeks, with an onset before 16 y/o.
Causes and Risk Factors
The exact underlying cause remains unknown [Ref]
- More common in females
- Genetic factors play a major role
Clinical Features
The hallmark feature of JIA is chronic arthritis (lasting >6 weeks) in a child (<16 y/o) +/- extra-articular manifestations depending on the JIA subtype. [Ref]
| Articular features | Typically presents as:
Most commonly affected joints:
The number and pattern of joint involvement varies, depending on the subtype:
|
| Extra-articular features | Constitutional symptoms
Dermatological:
Ophthalmological:
Other features:
|
Complications
Most common complications: [Ref]
- Leg-length discrepancy
- Joint contractures
Other complications: [Ref]
- Growth retardation
- Reduced bone mineral density
- Hip involvement may require joint replacement
- Amyloidosis
- Interstitial lung disease
Macrophage activation syndrome is an extremely severe complication, suggested by:
- Persistent high fever and CRP
- Low ESR and fibrinogen
- High or rising ferritin level (>1,000)
- Cytopaenia (at least 2 cell lineages) or falling cell counts
- High triglycerides and LFTs
Investigation and Diagnosis
JIA is a diagnosis of exclusion [Ref]
- No single objective test can definitively diagnose JIA
- A clinical diagnosis can only be made if there is chronic arthritis (>6 weeks) in a child (<16 y/o), after all other possible causes of chronic arthritis have been ruled out
Initial work-up for suspected JIA: [Ref]
- FBC, ESR, CRP (would show signs of inflammation – e.g. ↑ ESR/CRP)
- ANA
- Used to exclude differential diagnoses like SLE, mixed connective tissue disease
- +ve ANA is a major predictor and risk factor for developing chronic anterior uveitis [Ref]
- Rheumatoid factor, anti-CCP, HLA-B27
- They provide limited diagnostic value
- But they are mainly used to help classify the subtype, and their presence is associated with poor prognosis
- Imaging
- Initial test: X-ray (but cannot detect early JIA)
- Ultrasound
- MRI (most sensitive modality to detect early synovitis and demonstrate bone marrow oedema)
It is important to perform the following complication screening:
- Ophthalmic screening for uveitis is strongly recommended (every 3 months)
- JIA-associated chronic anterior uveitis is classically known to be insidious and asymptomatic
- Therefore, frequent screening is the only way to detect uveitis before leading to sight-threatening complications
- Note that +ve ANA is a major risk factor and predictor for the development of JIA-associated chronic anterior uveitis
- Consider lung disease screening (for those with systemic JIA)
Management
The mainstay disease-modifying therapy for JIA is DMARDs:
| JIA type | Management |
|---|---|
| Non-systemic JIA | 1st line:
Adjuncts
|
| Systemic JIA | 1st line: biological DMARD
Monotherapy of conventional DMARDs or NSAIDs is NOT recommended |
Management of JIA-associated uveitis:
- Topical steroid eye drops (prednisolone) for short-term management
- DMARDs (methotrexate or adalimumab) are used to taper off steroid eye drops