Juvenile Idiopathic Arthritis

Juvenile idiopathic arthritis (JIA) is arthritis that starts before 16 years of age, lasts 6 weeks or more and has no other identifiable cause.

It is the most common chronic inflammatory arthritis of childhood, with a UK prevalence of about 1 in 1,000. It is a group of distinct conditions, classified by the International League of Associations for Rheumatology (ILAR) into 7 categories.

It is often missed because swelling in a child can be painless and is put down to injury or growing pains. Untreated, it causes joint damage, growth disturbance and sight-threatening uveitis.

Inflamed synovium erodes cartilage and bone, as in adult rheumatoid arthritis, but in a growing skeleton. Cytokine drivers differ by category: systemic JIA is driven mainly by interleukin-1 (IL-1) and IL-6.

Growth disturbance is the distinctly paediatric consequence:

• •Synovitis next to a growth plate can accelerate local growth: chronic knee synovitis lengthens the affected leg
• •Prolonged inflammation can cause premature physeal fusion, shortening or angular deformity
• •Temporomandibular joint (TMJ) arthritis is often silent early and can cause micrognathia

Chronic anterior uveitis is usually painless with a white eye, so it is found only on slit-lamp examination. Cataract or glaucoma may already be present when symptoms appear.