How is JIA diagnosed ?
JIA is a diagnosis of exclusion.
Making a diagnosis of JIA relies on careful clinical assessment (history and examination), 'bedside' evaluation and a high index of suspicion with investigations helping to exclude other pathology including malignancy and infection.
Synovial biopsy is not needed to diagnose JIA and should be avoided unless there is high suspicion of malignancy or Tuberculosis.
Careful clinical assessment can differentiate between inflammatory joint conditions such as JIA, mechanical causes of joint pains, and other conditions causing joint pain and swelling.
The pattern of joint involvement is important:
- Single or multiple joints.
- Axial or peripheral or proximal.
- Additive / migratory or intermittent.
- Symmetry or asymmetry.
- Extra-articular features (rash [psoriasis], uveitis, multisystem involvement).
The differential diagnosis for JIA is extensive with conditions ranging from the benign (e.g., hypermobility) to the life threatening red flag conditions (e.g., malignancy, such as leukaemia and solid tumours, infection, non-accidental injury). Persistent fever (more than 7 days and is of a quotidian pattern, i.e., high in the evenings) suggests systemic JIA and it is important to check for rash especially in the evenings when the fever is high - the rash may be more on the inner thighs, inner arms or trunk.
Laboratory tests are seldom diagnostic but may help to exclude other diagnoses and be used by specialist teams to monitor disease activity and adverse effects of immunosuppressive drugs.
Investigations are likely to include as a minimum, full [complete] blood count (and peripheral smear [blood film] and Lactate Dehydrogenase [LDH] to help exclude malignancy), acute phase reactants (ESR, CRP and occasionally Ferritin) and pending the clinical context, blood cultures or serology for infection (e.g., streptococcal infection, yersinia for reactive arthritis), autoantibodies, Antinuclear antibodies - not diagnostic but in the context of JIA, increases the risk of chronic anterior uveitis).
HLA B27 - The presence of HLA B27 is common in many healthy people. In the presence of inflammatory arthritis, HLA B27 can associate with axial spine involvement (which may present later on with pain / stiffness in the neck or lower back) and acute uveitis (which will cause a painful red eye and is different to the chronic anterior uveitis observed in many cases of JIA). The presence of HLA B27 has implications for monitoring and eye screening as it associates with acute uveitis in Enthesitis Related Arthritis. In the context of oligoarticular JIA and enthesitis, the presence of HLA B27 may predict increased likelihood of axial spine involvement (sacroiliitis); notably HLA B27 status is not diagnostic and even if negative, with inflammatory back pain, further investigation is needed with imaging MRI.
Imaging such as radiographs, ultrasound or MRI may be needed but if the latter is performed, then using gadolinium is very sensitive to detect synovitis. MRI of the spine and sacroiliac joints (with gadolinium) is warranted if the presentation suggests inflammatory back pain as a feature of JIA; radiographs are very difficult to interpret in adolescents and the radiation exposure is considerable.
If JIA is suspected, then slit lamp examination for chronic anterior uveitis is warranted.
However, blood tests and radiographs are initially often normal in JIA, which can provide false reassurance at the time of presentation.
If there is clinical concern, then referral to a paediatric rheumatology for specialist assessment should NOT be delayed.