Juvenile Idiopathic Arthritis- diagnosis
No laboratory tests, or imaging can ‘prove’ that a child does, or does not, have JIA. The suspicion of JIA diagnosis rests on careful clinical assessment.
A diagnosis of JIA can be made when a child younger than 16 years old has had an episode of arthritis lasting for more than six weeks and all other diseases that could cause arthritis have been ruled out.
The diagnosis of JIA is, therefore, based on the presence and persistence of arthritis and the careful exclusion of any other disease by medical history, physical examination and laboratory tests.
The pattern of joint involvement is important in the differential diagnosis and deciding on the JIA subtype:
- Single / additive / intermittent or multiple joints.
- Axial or peripheral or proximal.
- Additive / migratory or intermittent.
- Symmetry or asymmetry.
- Extra-articular features (rash [psoriasis], uveitis, nodules).
- Multisystem involvement.
Typical patterns include:
- Asymmetric, small and large joints and distal interphalangeal joint involvement is typical of psoriatic arthritis.
- Symmetric, small and large joints is typical of polyarticular JIA.
- Hip involvement and enthesitis is typical of Enthesitis-Related Arthritis.
- Large joint and intermittent / flitting involvement is typical of acute rheumatic fever.
- Fever, rash and serositis and later symmetrical involvement of small and large joints (including distal small joints of the hands, ankle or wrist involvement) are typical of systemic JIA.
Laboratory tests for suspected JIA are seldom diagnostic but help to exclude other diagnoses (including malignancy and infection) and are used to monitor disease activity and adverse effects of immunosuppressive drugs. Antinuclear antibodies (ANA) are positive in around half the children with oligo-articular JIA. However, a small number of normal, healthy children also have a positive ANA, so a positive result does not always mean a child has JIA. A positive ANA in a child with JIA may help identify children at higher risk of developing chronic anterior uveitis. Rheumatoid factor is invariably not detected in JIA but can predict a worse prognosis once JIA is diagnosed. HLA-B27 is positive in up to 80% of patients with Enthesitis-Related Arthritis albeit can be detected in the general population (5-12%). Erythrocyte Sedimentation Rate (ESR), or C-reactive protein (CRP) measure extent of general inflammation and are useful in disease monitoring but can be normal in JIA. Radiographs are useful to assess any damage to the joint, but rarely show any abnormality in early stages of arthritis; they are useful to exclude other causes of joint pain (e.g., trauma / tumour). In cases where there is diagnostic difficulty ultrasound or MRI scan may be needed.
Synovial biopsy is not needed to make a diagnosis of JIA. Biopsy is only indicated if there is suspicion of Tuberculosis (TB) or malignancy.
If there is clinical suspicion that a child has JIA, then referral to a paediatric rheumatology team for specialist assessment should NOT be delayed by waiting for tests. Time from onset to diagnosis and starting treatment is important - the shorter the interval the better the outcome. In particular, any child suspected of having JIA should be referred for eye screening to detect chronic anterior uveitis (usually without pain or visual symptoms in early stages) and if not detected can result in blindness.
The photograph below shows a blind eye due to cataract and band keratopathy due to chronic uveitis related to JIA
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 differential diagnosis for JIA is extensive with conditions ranging from the benign (e.g., hypermobility) to the life threatening (e.g., malignancy, such as leukaemia and solid tumours, infection, non-accidental injury). The presence of any ‘red flags’, such as weight loss, fever, night pain and bone tenderness, suggests infection or malignancy and warrants urgent assessment in secondary care.
The clinical assessment of a child is not the same as that of an adult. The young child may not be able to verbalize pain and the history may be primarily from the parents or caregivers, or from observations made by teachers and may initially be vague - e.g., 'my child is not quite right' or 'my child is limping'. Examination findings need to be interpreted in the context of normal development.
Clues in the clinical assessment to suggest inflammatory disease:
- Change in behaviour – such as being more irritable, clingy, or reluctant to play.
- Avoidance of activities previously enjoyed (e.g., in play or sport).
- Regression of achieved motor milestones (such as walking or handwriting).
- Morning joint stiffness and pain - the child may be ‘slow to get going in the morning’ or experiences stiffness after periods of rest, such as after long car rides – this is called ‘gelling’.
The history alone may not localise the site of problems and assessment must include, as a minimum, pGALS, followed by pREMS of the relevant joints.