Single joint: Always consider infection and malignancy. In at-risk groups, consider mycobacterial disease and rheumatic.. Always check for red flags.

Multiple joints: Wide spectrum of causes including inflammatory, reactive, multi-system disease (connective tissue diseases/vasculitis), metabolic and malignancy.

Common pitfalls in making a diagnosis of JIA include:

• Belief children can’t get arthritis (they can)
• Attributing swelling to trauma without clear history
• False reassurance from normal bloods/radiographs
• Assuming absence of RF excludes JIA
• Believing pain must be present (25% of children and young people have painless arthritis)
• Consider arthritis in children with Down syndrome if change in functional abilities

Diagnosis: Clinical assessment is key. Swelling post-trauma (e.g., sprain) should resolve in days. If systemic upset or fever, refer to paediatric rheumatology/orthopaedics promptly.

Hypermobility: Can show mild, transient swelling (often knees) post-activity which resolves spontaneously. Persistent swelling warrants referral.

Reactive Arthritis: Follows infections which can be mild or without symptoms (eg. respiratory, gastrointestinal, sexually acquired). Limp may occur. Typically self-resolves in weeks. Rule out septic arthritis/osteomyelitis. In Māori/Pacific children, consider rheumatic Refer if symptoms persist for more than 3 weeks.

JIA: Most common cause if no trauma, infection, or rheumatic fever. Often presents as a single swollen knee/ankle in a well child. Normal bloods/radiographs don’t exclude it.

Uveitis Risk: JIA may cause asymptomatic chronic anterior uveitis. Early ophthalmology screening is vital.

Connective Tissue Disorders (CTDs): Present with a spectrum of features, often presenting with arthralgia rather than true arthritis.

Referral: Early referral to paediatric rheumatology improves outcomes regardless of the underlying rheumatic disease.