How is JIA diagnosed ?
Juvenile Idiopathic Arthritis (JIA) is a diagnosis of exclusion. Diagnosis relies on careful clinical assessment, supported by targeted investigations to exclude other serious conditions such as infection and malignancy.
Assessment should include a detailed history and examination, ‘bedside ‘functional assessment, an understanding of the pattern of joint involvement, and a high index of suspicion.
A synovial biopsy is not required to diagnose JIA and should be avoided unless there is a specific concern for malignancy or tuberculosis.
Clinical assessment
- Single or multiple joints involved
- Axial, peripheral or proximal distribution
- Pattern over time: additive, migratory or intermittent
- Symmetry or asymmetry
- Extra-articular features such as rash (including psoriasis), uveitis or multisystem involvement
The differential diagnosis is broad, ranging from benign conditions (for example hypermobility) to serious red flag conditions including infection, malignancy (such as leukaemia or solid tumours) and non-accidental injury.
A persistent fever lasting more than 7 days, particularly with a quotidian (evening) pattern, should raise suspicion of systemic JIA. A rash may be more visible during fever spikes and is often seen on the inner thighs, inner arms or trunk.
Investigations
- Full blood count with blood film and LDH (to help exclude malignancy)
- Inflammatory markers (ESR, CRP, and sometimes ferritin)
- Infection screening guided by clinical context (e.g. blood cultures, streptococcal or yersinia serology)
- Autoantibodies including ANA (associated with increased risk of chronic anterior uveitis in JIA)
HLA-B27
HLA-B27 is present in many healthy individuals and is not diagnostic of JIA. In the context of inflammatory arthritis it may be associated with axial involvement (neck or lower back pain and stiffness) and acute uveitis (painful red eye).
In children with enthesitis-related arthritis, HLA-B27 positivity has implications for monitoring and eye assessment. MRI of the sacroiliac joints and spine is often required if axial disease is suspected, even if HLA-B27 is negative.
Imaging
Imaging may include ultrasound, radiographs or MRI. MRI with gadolinium contrast is particularly sensitive for detecting synovitis. MRI of the spine and sacroiliac joints is indicated if inflammatory back pain is suspected. Plain radiographs in adolescents can be difficult to interpret and involve radiation exposure.
Eye screening
If JIA is suspected, a slit lamp examination should be arranged to screen for chronic anterior uveitis.
Key clinical point
Early in the disease, blood tests and imaging may be normal, which can give false reassurance. If there is ongoing clinical concern, referral to a paediatric rheumatology service should not be delayed, even if initial investigations are unremarkable.
