Juvenile Idiopathic Arthritis and Other Chronic Arthritides
Classification
JIA is arthritis of unknown cause beginning before age 16 and persisting at least 6 weeks. ILAR categories - oligoarticular (≤4 joints), RF-positive polyarticular, RF-negative polyarticular, systemic, psoriatic, enthesitis-related, and undifferentiated - remain clinically useful even as newer consensus views JIA as one disease with subtypes.
Patterns and pitfalls
Oligoarticular JIA peaks at ages 1–3, is more common in girls, and carries the highest uveitis risk when ANA positive with young onset; uveitis is usually silent, so slit-lamp intervals are risk-stratified (often every 3 months in the highest-risk group). Systemic JIA is a diagnosis of exclusion: quotidian fever, evanescent salmon rash, serositis, hepatosplenomegaly, and marked acute-phase response. Watch for macrophage activation syndrome - falling platelets and fibrinogen with rising ferritin and triglycerides. Enthesitis-related arthritis affects older boys, involves entheses and axial skeleton, associates with HLA-B27, and predisposes to painful acute anterior uveitis rather than silent chronic uveitis. Psoriatic JIA features dactylitis, nail pitting, and family history of psoriasis.
Treatment
NSAIDs and intra-articular triamcinolone hexacetonide for oligoarthritis; methotrexate is the conventional anchor for polyarthritis; TNF inhibitors, abatacept, tocilizumab, and IL-1 blockade (for systemic JIA) follow treat-to-target principles. Physical therapy and ophthalmologic surveillance are part of the prescription, not add-ons.
Rule of thumb
A young child with a swollen knee and a positive ANA needs a slit-lamp examination, not just an NSAID.